DBD::SQLite - Self-contained RDBMS in a DBI Driver
use DBI;
my $dbh = DBI->connect("dbi:SQLite:dbname=$dbfile","","");SQLite is a public domain file-based relational database engine that you can find at https://www.sqlite.org/.
DBD::SQLite is a Perl DBI driver for SQLite, that includes the entire thing in the distribution. So in order to get a fast transaction capable RDBMS working for your perl project you simply have to install this module, and nothing else.
SQLite supports the following features:
See https://www.sqlite.org/lang.html for details.
Everything for your database is stored in a single disk file, making it easier to move things around than with DBD::CSV.
Yes, DBD::SQLite is small and light, but it supports full transactions!
User-defined aggregate or regular functions can be registered with the SQL parser.
There's lots more to it, so please refer to the docs on the SQLite web page, listed above, for SQL details. Also refer to DBI for details on how to use DBI itself. The API works like every DBI module does. However, currently many statement attributes are not implemented or are limited by the typeless nature of the SQLite database.
DBD::SQLite is usually compiled with a bundled SQLite library (SQLite version 3.46.1 as of this release) for consistency. However, a different version of SQLite may sometimes be used for some reasons like security, or some new experimental features.
You can look at $DBD::SQLite::sqlite_version (3.x.y format) or $DBD::SQLite::sqlite_version_number (3xxxyyy format) to find which version of SQLite is actually used. You can also check DBD::SQLite::Constants::SQLITE_VERSION_NUMBER().
You can also find how the library is compiled by calling DBD::SQLite::compile_options() (see below).
SQLite creates a file per a database. You should pass the path of the database file (with or without a parent directory) in the DBI connection string (as a database name):
my $dbh = DBI->connect("dbi:SQLite:dbname=$dbfile","","");The file is opened in read/write mode, and will be created if it does not exist yet.
Although the database is stored in a single file, the directory containing the database file must be writable by SQLite because the library will create several temporary files there.
If the filename $dbfile is ":memory:", then a private, temporary in-memory database is created for the connection. This in-memory database will vanish when the database connection is closed. It is handy for your library tests.
Note that future versions of SQLite might make use of additional special filenames that begin with the ":" character. It is recommended that when a database filename actually does begin with a ":" character you should prefix the filename with a pathname such as "./" to avoid ambiguity.
If the filename $dbfile is an empty string, then a private, temporary on-disk database will be created. This private database will be automatically deleted as soon as the database connection is closed.
As of 1.41_01, you can pass URI filename (see https://www.sqlite.org/uri.html) as well for finer control:
my $dbh = DBI->connect("dbi:SQLite:uri=file:$path_to_dbfile?mode=rwc");Note that this is not for remote SQLite database connection. You can only connect to a local database.
You can set sqlite_open_flags (only) when you connect to a database:
use DBD::SQLite::Constants qw/:file_open/;
my $dbh = DBI->connect("dbi:SQLite:$dbfile", undef, undef, {
sqlite_open_flags => SQLITE_OPEN_READONLY,
});See https://www.sqlite.org/c3ref/open.html for details.
As of 1.49_05, you can also make a database read-only by setting ReadOnly attribute to true (only) when you connect to a database. Actually you can set it after you connect, but in that case, it can't make the database read-only, and you'll see a warning (which you can hide by turning PrintWarn off).
When you use File::Temp to create a temporary file/directory for SQLite databases, you need to remember:
You may want to use tempfile() to create a temporary database filename for DBD::SQLite, but as noted in File::Temp's POD, this file may have an exclusive lock under some operating systems (notably Mac OSX), and result in a "database is locked" error. To avoid this, set EXLOCK option to false when you call tempfile().
($fh, $filename) = tempfile($template, EXLOCK => 0);When you set CLEANUP option to true when you create a temporary directory with tempdir() or newdir(), you may have to disconnect databases explicitly before the temporary directory is gone (notably under MS Windows).
(The above is quoted from the pod of File::Temp.)
If you don't need to keep or share a temporary database, use ":memory:" database instead. It's much handier and cleaner for ordinary testing.
Follow the advice in the SQLite FAQ (https://sqlite.org/faq.html).
Under Unix, you should not carry an open SQLite database across a fork() system call into the child process. Problems will result if you do.
You shouldn't (re)use a database handle you created (probably to set up a database schema etc) before you fork(). Otherwise, you might see a database corruption in the worst case.
If you need to fork(), (re)open a database after you fork(). You might also want to tweak sqlite_busy_timeout and sqlite_use_immediate_transaction (see below), depending on your needs.
If you need a higher level of concurrency than SQLite supports, consider using other client/server database engines.
To access the database from the command line, try using dbish which comes with the DBI::Shell module. Just type:
dbish dbi:SQLite:foo.dbOn the command line to access the file foo.db.
Alternatively you can install SQLite from the link above without conflicting with DBD::SQLite and use the supplied sqlite3 command line tool.
As of version 1.11, blobs should "just work" in SQLite as text columns. However this will cause the data to be treated as a string, so SQL statements such as length(x) will return the length of the column as a NUL terminated string, rather than the size of the blob in bytes. In order to store natively as a BLOB use the following code:
use DBI qw(:sql_types);
my $dbh = DBI->connect("dbi:SQLite:dbfile","","");
my $blob = `cat foo.jpg`;
my $sth = $dbh->prepare("INSERT INTO mytable VALUES (1, ?)");
$sth->bind_param(1, $blob, SQL_BLOB);
$sth->execute();And then retrieval just works:
$sth = $dbh->prepare("SELECT * FROM mytable WHERE id = 1");
$sth->execute();
my $row = $sth->fetch;
my $blobo = $row->[1];
# now $blobo == $blobAs of this writing, a SQL that compares a return value of a function with a numeric bind value like this doesn't work as you might expect.
my $sth = $dbh->prepare(q{
SELECT bar FROM foo GROUP BY bar HAVING count(*) > ?;
});
$sth->execute(5);This is because DBD::SQLite assumes that all the bind values are text (and should be quoted) by default. Thus the above statement becomes like this while executing:
SELECT bar FROM foo GROUP BY bar HAVING count(*) > "5";There are four workarounds for this.
As shown above in the BLOB section, you can always use bind_param() to tell the type of a bind value.
use DBI qw(:sql_types); # Don't forget this
my $sth = $dbh->prepare(q{
SELECT bar FROM foo GROUP BY bar HAVING count(*) > ?;
});
$sth->bind_param(1, 5, SQL_INTEGER);
$sth->execute();This is somewhat weird, but works anyway.
my $sth = $dbh->prepare(q{
SELECT bar FROM foo GROUP BY bar HAVING count(*) > (? + 0);
});
$sth->execute(5);This is more explicit way to do the above.
my $sth = $dbh->prepare(q{
SELECT bar FROM foo GROUP BY bar HAVING count(*) > cast(? as integer);
});
$sth->execute(5);sqlite_see_if_its_a_number database handle attributeAs of version 1.32_02, you can use sqlite_see_if_its_a_number to let DBD::SQLite to see if the bind values are numbers or not.
$dbh->{sqlite_see_if_its_a_number} = 1;
my $sth = $dbh->prepare(q{
SELECT bar FROM foo GROUP BY bar HAVING count(*) > ?;
});
$sth->execute(5);You can set it to true when you connect to a database.
my $dbh = DBI->connect('dbi:SQLite:foo', undef, undef, {
AutoCommit => 1,
RaiseError => 1,
sqlite_see_if_its_a_number => 1,
});This is the most straightforward solution, but as noted above, existing data in your databases created by DBD::SQLite have not always been stored as numbers, so this *might* cause other obscure problems. Use this sparingly when you handle existing databases. If you handle databases created by other tools like native sqlite3 command line tool, this attribute would help you.
As of 1.41_04, sqlite_see_if_its_a_number works only for bind values with no explicit type.
my $dbh = DBI->connect('dbi:SQLite:foo', undef, undef, {
AutoCommit => 1,
RaiseError => 1,
sqlite_see_if_its_a_number => 1,
});
my $sth = $dbh->prepare('INSERT INTO foo VALUES(?)');
# '1.230' will be inserted as a text, instead of 1.23 as a number,
# even though sqlite_see_if_its_a_number is set.
$sth->bind_param(1, '1.230', SQL_VARCHAR);
$sth->execute;SQLite supports several placeholder expressions, including ? and :AAAA. Consult the DBI and SQLite documentation for details.
https://www.sqlite.org/lang_expr.html#varparam
Note that a question mark actually means a next unused (numbered) placeholder. You're advised not to use it with other (numbered or named) placeholders to avoid confusion.
my $sth = $dbh->prepare(
'update TABLE set a=?1 where b=?2 and a IS NOT ?1'
);
$sth->execute(1, 2); SQLite has a set of "Pragma"s to modify its operation or to query for its internal data. These are specific to SQLite and are not likely to work with other DBD libraries, but you may find some of these are quite useful, including:
You can use this pragma to change the journal mode for SQLite databases, maybe for better performance, or for compatibility.
Its default mode is DELETE, which means SQLite uses a rollback journal to implement transactions, and the journal is deleted at the conclusion of each transaction. If you use TRUNCATE instead of DELETE, the journal will be truncated, which is usually much faster.
A WAL (write-ahead log) mode is introduced as of SQLite 3.7.0. This mode is persistent, and it stays in effect even after closing and reopening the database. In other words, once the WAL mode is set in an application or in a test script, the database becomes inaccessible by older clients. This tends to be an issue when you use a system sqlite3 executable under a conservative operating system.
To fix this, You need to issue PRAGMA journal_mode = DELETE (or TRUNCATE) beforehand, or install a newer version of sqlite3.
If you happen to need to create a SQLite database that will also be accessed by a very old SQLite client (prior to 3.3.0 released in Jan. 2006), you need to set this pragma to ON before you create a database.
You can set this pragma to ON to reverse the order of results of SELECT statements without an ORDER BY clause so that you can see if applications are making invalid assumptions about the result order.
Note that SQLite 3.7.15 (bundled with DBD::SQLite 1.38_02) enhanced its query optimizer and the order of results of a SELECT statement without an ORDER BY clause may be different from the one of the previous versions.
You can set set this pragma to OFF to make some of the operations in SQLite faster with a possible risk of database corruption in the worst case. See also "Performance" section below.
See https://www.sqlite.org/pragma.html for more details.
SQLite has started supporting foreign key constraints since 3.6.19 (released on Oct 14, 2009; bundled in DBD::SQLite 1.26_05). To be exact, SQLite has long been able to parse a schema with foreign keys, but the constraints has not been enforced. Now you can issue a foreign_keys pragma to enable this feature and enforce the constraints, preferably as soon as you connect to a database and you're not in a transaction:
$dbh->do("PRAGMA foreign_keys = ON");And you can explicitly disable the feature whenever you like by turning the pragma off:
$dbh->do("PRAGMA foreign_keys = OFF");As of this writing, this feature is disabled by default by the SQLite team, and by us, to secure backward compatibility, as this feature may break your applications, and actually broke some for us. If you have used a schema with foreign key constraints but haven't cared them much and supposed they're always ignored for SQLite, be prepared, and please do extensive testing to ensure that your applications will continue to work when the foreign keys support is enabled by default.
See https://www.sqlite.org/foreignkeys.html for details.
DBI/DBD::SQLite's transactions may be a bit confusing. They behave differently according to the status of the AutoCommit flag:
You're supposed to always use the auto-commit mode, except you explicitly begin a transaction, and when the transaction ended, you're supposed to go back to the auto-commit mode. To begin a transaction, call begin_work method, or issue a BEGIN statement. To end it, call commit/rollback methods, or issue the corresponding statements.
$dbh->{AutoCommit} = 1;
$dbh->begin_work; # or $dbh->do('BEGIN TRANSACTION');
# $dbh->{AutoCommit} is turned off temporarily during a transaction;
$dbh->commit; # or $dbh->do('COMMIT');
# $dbh->{AutoCommit} is turned on again;You're supposed to always use the transactional mode, until you explicitly turn on the AutoCommit flag. You can explicitly issue a BEGIN statement (only when an actual transaction has not begun yet) but you're not allowed to call begin_work method (if you don't issue a BEGIN, it will be issued internally). You can commit or roll it back freely. Another transaction will automatically begin if you execute another statement.
$dbh->{AutoCommit} = 0;
# $dbh->do('BEGIN TRANSACTION') is not necessary, but possible
...
$dbh->commit; # or $dbh->do('COMMIT');
# $dbh->{AutoCommit} stays intact;
$dbh->{AutoCommit} = 1; # ends the transactional modeThis AutoCommit mode is independent from the autocommit mode of the internal SQLite library, which always begins by a BEGIN statement, and ends by a COMMIT or a ROLLBACK.
The default transaction behavior of SQLite is deferred, that means, locks are not acquired until the first read or write operation, and thus it is possible that another thread or process could create a separate transaction and write to the database after the BEGIN on the current thread has executed, and eventually cause a "deadlock". To avoid this, DBD::SQLite internally issues a BEGIN IMMEDIATE if you begin a transaction by calling begin_work or by turning off AutoCommit (since 1.38_01).
If you really need to turn off this feature for some reasons, set sqlite_use_immediate_transaction database handle attribute to false, and the default deferred transaction will be used.
my $dbh = DBI->connect("dbi:SQLite::memory:", "", "", {
sqlite_use_immediate_transaction => 0,
});Or, issue a BEGIN statement explicitly each time you begin a transaction.
See http://sqlite.org/lockingv3.html for locking details.
$sth->finish and Transaction RollbackAs the DBI doc says, you almost certainly do not need to call "finish" in DBI method if you fetch all rows (probably in a loop). However, there are several exceptions to this rule, and rolling-back of an unfinished SELECT statement is one of such exceptional cases.
SQLite prohibits ROLLBACK of unfinished SELECT statements in a transaction (See http://sqlite.org/lang_transaction.html for details). So you need to call finish before you issue a rollback.
$sth = $dbh->prepare("SELECT * FROM t");
$dbh->begin_work;
eval {
$sth->execute;
$row = $sth->fetch;
...
die "For some reason";
...
};
if($@) {
$sth->finish; # You need this for SQLite
$dbh->rollback;
} else {
$dbh->commit;
}DBI's statement handle is not supposed to process multiple statements at a time. So if you pass a string that contains multiple statements (a dump) to a statement handle (via prepare or do), DBD::SQLite only processes the first statement, and discards the rest.
If you need to process multiple statements at a time, set a sqlite_allow_multiple_statements attribute of a database handle to true when you connect to a database, and do method takes care of the rest (since 1.30_01, and without creating DBI's statement handles internally since 1.47_01). If you do need to use prepare or prepare_cached (which I don't recommend in this case, because typically there's no placeholder nor reusable part in a dump), you can look at $sth->{sqlite_unprepared_statements} to retrieve what's left, though it usually contains nothing but white spaces.
Because of historical reasons, DBD::SQLite's TYPE statement handle attribute returns an array ref of string values, contrary to the DBI specification. This value is also less useful for SQLite users because SQLite uses dynamic type system (that means, the datatype of a value is associated with the value itself, not with its container).
As of version 1.61_02, if you set sqlite_prefer_numeric_type database handle attribute to true, TYPE statement handle attribute returns an array of integer, as an experiment.
SQLite is fast, very fast. Matt processed his 72MB log file with it, inserting the data (400,000+ rows) by using transactions and only committing every 1000 rows (otherwise the insertion is quite slow), and then performing queries on the data.
Queries like count(*) and avg(bytes) took fractions of a second to return, but what surprised him most of all was:
SELECT url, count(*) as count
FROM access_log
GROUP BY url
ORDER BY count desc
LIMIT 20To discover the top 20 hit URLs on the site (http://axkit.org), and it returned within 2 seconds. He was seriously considering switching his log analysis code to use this little speed demon!
Oh yeah, and that was with no indexes on the table, on a 400MHz PIII.
For best performance be sure to tune your hdparm settings if you are using linux. Also you might want to set:
PRAGMA synchronous = OFFWhich will prevent SQLite from doing fsync's when writing (which slows down non-transactional writes significantly) at the expense of some peace of mind. Also try playing with the cache_size pragma.
The memory usage of SQLite can also be tuned using the cache_size pragma.
$dbh->do("PRAGMA cache_size = 800000");The above will allocate 800M for DB cache; the default is 2M. Your sweet spot probably lies somewhere in between.
Returns the version of the SQLite library which DBD::SQLite is using, e.g., "3.26.0". Can only be read.
SQLite strings are simple arrays of bytes, but Perl strings can store any arbitrary Unicode code point. Thus, DBD::SQLite has to adopt some method of translating between those two models. This parameter defines that translation.
Accepted values are the following constants:
DBD_SQLITE_STRING_MODE_BYTES: All strings are assumed to represent bytes. A Perl string that contains any code point above 255 will trigger an exception. This is appropriate for Latin-1 strings, binary data, pre-encoded UTF-8 strings, etc.
DBD_SQLITE_STRING_MODE_UNICODE_FALLBACK: All Perl strings are encoded to UTF-8 before being given to SQLite. Perl will try to decode SQLite strings as UTF-8 when giving them to Perl. Should any such string not be valid UTF-8, a warning is thrown, and the string is left undecoded.
This is appropriate for strings that are decoded to characters via, e.g., "decode" in Encode.
Also note that, due to some bizarreness in SQLite's type system (see https://www.sqlite.org/datatype3.html), if you want to retain blob-style behavior for some columns under DBD_SQLITE_STRING_MODE_UNICODE_FALLBACK (say, to store images in the database), you have to state so explicitly using the 3-argument form of "bind_param" in DBI when doing updates:
use DBI qw(:sql_types);
use DBD::SQLite::Constants ':dbd_sqlite_string_mode';
$dbh->{sqlite_string_mode} = DBD_SQLITE_STRING_MODE_UNICODE_FALLBACK;
my $sth = $dbh->prepare("INSERT INTO mytable (blobcolumn) VALUES (?)");
# Binary_data will be stored as is.
$sth->bind_param(1, $binary_data, SQL_BLOB);Defining the column type as BLOB in the DDL is not sufficient.
DBD_SQLITE_STRING_MODE_UNICODE_STRICT: Like DBD_SQLITE_STRING_MODE_UNICODE_FALLBACK but usually throws an exception rather than a warning if SQLite sends invalid UTF-8. (In Perl callbacks from SQLite we still warn instead.)
DBD_SQLITE_STRING_MODE_UNICODE_NAIVE: Like DBD_SQLITE_STRING_MODE_UNICODE_FALLBACK but uses a "naïve" UTF-8 decoding method that forgoes validation. This is marginally faster than a validated decode, but it can also corrupt Perl itself!
DBD_SQLITE_STRING_MODE_PV (default, but DO NOT USE): Like DBD_SQLITE_STRING_MODE_BYTES, but when translating Perl strings to SQLite the Perl string's internal byte buffer is given to SQLite. This is bad, but it's been the default for many years, and changing that would break existing applications.
sqlite_unicode or unicode (deprecated)If truthy, equivalent to setting sqlite_string_mode to DBD_SQLITE_STRING_MODE_UNICODE_NAIVE; if falsy, equivalent to DBD_SQLITE_STRING_MODE_PV.
Prefer sqlite_string_mode in all new code.
If you set this to true, do method will process multiple statements at one go. This may be handy, but with performance penalty. See above for details.
If you set this to true, DBD::SQLite tries to issue a begin immediate transaction (instead of begin transaction) when necessary. See above for details.
As of version 1.38_01, this attribute is set to true by default. If you really need to use deferred transactions for some reasons, set this to false explicitly.
If you set this to true, DBD::SQLite tries to see if the bind values are number or not, and does not quote if they are numbers. See above for details.
If set to true, DBD::SQLite uses extended result codes where appropriate (see https://www.sqlite.org/rescode.html).
If set to true, language features that allow ordinary SQL to deliberately corrupt the database file are prohibited.
Returns an unprepared part of the statement you pass to prepare. Typically this contains nothing but white spaces after a semicolon. See above for details.
See also to the DBI documentation for the details of other common methods.
$sth = $dbh->table_info(undef, $schema, $table, $type, \%attr);Returns all tables and schemas (databases) as specified in "table_info" in DBI. The schema and table arguments will do a LIKE search. You can specify an ESCAPE character by including an 'Escape' attribute in \%attr. The $type argument accepts a comma separated list of the following types 'TABLE', 'INDEX', 'VIEW', 'TRIGGER', 'LOCAL TEMPORARY' and 'SYSTEM TABLE' (by default all are returned). Note that a statement handle is returned, and not a direct list of tables.
The following fields are returned:
TABLE_CAT: Always NULL, as SQLite does not have the concept of catalogs.
TABLE_SCHEM: The name of the schema (database) that the table or view is in. The default schema is 'main', temporary tables are in 'temp' and other databases will be in the name given when the database was attached.
TABLE_NAME: The name of the table or view.
TABLE_TYPE: The type of object returned. Will be one of 'TABLE', 'INDEX', 'VIEW', 'TRIGGER', 'LOCAL TEMPORARY' or 'SYSTEM TABLE'.
@names = $dbh->primary_key(undef, $schema, $table);
$sth = $dbh->primary_key_info(undef, $schema, $table, \%attr);You can retrieve primary key names or more detailed information. As noted above, SQLite does not have the concept of catalogs, so the first argument of the methods is usually undef, and you'll usually set undef for the second one (unless you want to know the primary keys of temporary tables).
$sth = $dbh->foreign_key_info(undef, $pk_schema, $pk_table,
undef, $fk_schema, $fk_table);Returns information about foreign key constraints, as specified in "foreign_key_info" in DBI, but with some limitations :
information in rows returned by the $sth is incomplete with respect to the "foreign_key_info" in DBI specification. All requested fields are present, but the content is undef for some of them.
The following nonempty fields are returned :
PKTABLE_NAME: The primary (unique) key table identifier.
PKCOLUMN_NAME: The primary (unique) key column identifier.
FKTABLE_NAME: The foreign key table identifier.
FKCOLUMN_NAME: The foreign key column identifier.
KEY_SEQ: The column sequence number (starting with 1), when several columns belong to a same constraint.
UPDATE_RULE: The referential action for the UPDATE rule. The following codes are defined:
CASCADE 0
RESTRICT 1
SET NULL 2
NO ACTION 3
SET DEFAULT 4Default is 3 ('NO ACTION').
DELETE_RULE: The referential action for the DELETE rule. The codes are the same as for UPDATE_RULE.
DEFERRABILITY: The following codes are defined:
INITIALLY DEFERRED 5
INITIALLY IMMEDIATE 6
NOT DEFERRABLE 7UNIQUE_OR_PRIMARY: Whether the column is primary or unique.
Note: foreign key support in SQLite must be explicitly turned on through a PRAGMA command; see "Foreign keys" earlier in this manual.
$sth = $dbh->statistics_info(undef, $schema, $table,
$unique_only, $quick);Returns information about a table and it's indexes, as specified in "statistics_info" in DBI, but with some limitations :
information in rows returned by the $sth is incomplete with respect to the "statistics_info" in DBI specification. All requested fields are present, but the content is undef for some of them.
The following nonempty fields are returned :
TABLE_SCHEM: The name of the schema (database) that the table is in. The default schema is 'main', temporary tables are in 'temp' and other databases will be in the name given when the database was attached.
TABLE_NAME: The name of the table
NON_UNIQUE: Contains 0 for unique indexes, 1 for non-unique indexes
INDEX_NAME: The name of the index
TYPE: SQLite uses 'btree' for all it's indexes
ORDINAL_POSITION: Column sequence number (starting with 1).
COLUMN_NAME: The name of the column
my $bool = $dbh->ping;returns true if the database file exists (or the database is in-memory), and the database connection is active.
The following methods can be called via the func() method with a little tweak, but the use of func() method is now discouraged by the DBI author for various reasons (see DBI's document https://metacpan.org/pod/DBI::DBD#Using-install_method()-to-expose-driver-private-methods for details). So, if you're using DBI >= 1.608, use these sqlite_ methods. If you need to use an older DBI, you can call these like this:
$dbh->func( ..., "(method name without sqlite_ prefix)" );Exception: sqlite_trace should always be called as is, even with func() method (to avoid conflict with DBI's trace() method).
$dbh->func( ..., "sqlite_trace");This method returns the last inserted rowid. If you specify an INTEGER PRIMARY KEY as the first column in your table, that is the column that is returned. Otherwise, it is the hidden ROWID column. See the SQLite docs for details.
Generally you should not be using this method. Use the DBI last_insert_id method instead. The usage of this is:
$h->last_insert_id($catalog, $schema, $table_name, $field_name [, \%attr ])Running $h->last_insert_id("","","","") is the equivalent of running $dbh->sqlite_last_insert_rowid() directly.
Retrieve the current (main) database filename. If the database is in-memory or temporary, this returns an empty string, or undef.
Retrieve the current busy timeout.
Set the current busy timeout. The timeout is in milliseconds.
This method will register a new function which will be usable in an SQL query. The method's parameters are:
The name of the function. This is the name of the function as it will be used from SQL.
The number of arguments taken by the function. If this number is -1, the function can take any number of arguments.
This should be a reference to the function's implementation.
You can optionally pass an extra flag bit to create_function, which then would be ORed with SQLITE_UTF8 (default). As of 1.47_02 (SQLite 3.8.9), only meaning bit is SQLITE_DETERMINISTIC (introduced at SQLite 3.8.3), which can make the function perform better. See C API documentation at http://sqlite.org/c3ref/create_function.html for details.
For example, here is how to define a now() function which returns the current number of seconds since the epoch:
$dbh->sqlite_create_function( 'now', 0, sub { return time } );After this, it could be used from SQL as:
INSERT INTO mytable ( now() );The function should return a scalar value, and the value is treated as a text (or a number if appropriate) by default. If you do need to specify a type of the return value (like BLOB), you can return a reference to an array that contains the value and the type, as of 1.65_01.
$dbh->sqlite_create_function( 'md5', 1, sub { return [md5($_[0]), SQL_BLOB] } );SQLite includes syntactic support for an infix operator 'REGEXP', but without any implementation. The DBD::SQLite driver automatically registers an implementation that performs standard perl regular expression matching, using current locale. So for example you can search for words starting with an 'A' with a query like
SELECT * from table WHERE column REGEXP '\bA\w+'If you want case-insensitive searching, use perl regex flags, like this :
SELECT * from table WHERE column REGEXP '(?i:\bA\w+)'The default REGEXP implementation can be overridden through the create_function API described above.
Note that regexp matching will not use SQLite indices, but will iterate over all rows, so it could be quite costly in terms of performance.
This method manually registers a new function which will be usable in an SQL query as a COLLATE option for sorting. Such functions can also be registered automatically on demand: see section "COLLATION FUNCTIONS" below.
The method's parameters are:
The name of the function exposed to SQL.
Reference to the function's implementation. The driver will check that this is a proper sorting function.
This method manually registers a callback function that will be invoked whenever an undefined collation sequence is required from an SQL statement. The callback is invoked as
$code_ref->($dbh, $collation_name)and should register the desired collation using "sqlite_create_collation".
An initial callback is already registered by DBD::SQLite, so for most common cases it will be simpler to just add your collation sequences in the %DBD::SQLite::COLLATION hash (see section "COLLATION FUNCTIONS" below).
This method will register a new aggregate function which can then be used from SQL. The method's parameters are:
The name of the aggregate function, this is the name under which the function will be available from SQL.
This is an integer which tells the SQL parser how many arguments the function takes. If that number is -1, the function can take any number of arguments.
This is the package which implements the aggregator interface.
You can optionally pass an extra flag bit to create_aggregate, which then would be ORed with SQLITE_UTF8 (default). As of 1.47_02 (SQLite 3.8.9), only meaning bit is SQLITE_DETERMINISTIC (introduced at SQLite 3.8.3), which can make the function perform better. See C API documentation at http://sqlite.org/c3ref/create_function.html for details.
The aggregator interface consists of defining three methods:
This method will be called once to create an object which should be used to aggregate the rows in a particular group. The step() and finalize() methods will be called upon the reference return by the method.
This method will be called once for each row in the aggregate.
This method will be called once all rows in the aggregate were processed and it should return the aggregate function's result. When there is no rows in the aggregate, finalize() will be called right after new().
Here is a simple aggregate function which returns the variance (example adapted from pysqlite):
package variance;
sub new { bless [], shift; }
sub step {
my ( $self, $value ) = @_;
push @$self, $value;
}
sub finalize {
my $self = $_[0];
my $n = @$self;
# Variance is NULL unless there is more than one row
return undef unless $n || $n == 1;
my $mu = 0;
foreach my $v ( @$self ) {
$mu += $v;
}
$mu /= $n;
my $sigma = 0;
foreach my $v ( @$self ) {
$sigma += ($v - $mu)**2;
}
$sigma = $sigma / ($n - 1);
return $sigma;
}
$dbh->sqlite_create_aggregate( "variance", 1, 'variance' );The aggregate function can then be used as:
SELECT group_name, variance(score)
FROM results
GROUP BY group_name;For more examples, see the DBD::SQLite::Cookbook.
This method registers a handler to be invoked periodically during long running calls to SQLite.
An example use for this interface is to keep a GUI updated during a large query. The parameters are:
The progress handler is invoked once for every $n_opcodes virtual machine opcodes in SQLite.
Reference to the handler subroutine. If the progress handler returns non-zero, the SQLite operation is interrupted. This feature can be used to implement a "Cancel" button on a GUI dialog box.
Set this argument to undef if you want to unregister a previous progress handler.
This method registers a callback function to be invoked whenever a transaction is committed. Any callback set by a previous call to sqlite_commit_hook is overridden. A reference to the previous callback (if any) is returned. Registering an undef disables the callback.
When the commit hook callback returns zero, the commit operation is allowed to continue normally. If the callback returns non-zero, then the commit is converted into a rollback (in that case, any attempt to explicitly call $dbh->rollback() afterwards would yield an error).
This method registers a callback function to be invoked whenever a transaction is rolled back. Any callback set by a previous call to sqlite_rollback_hook is overridden. A reference to the previous callback (if any) is returned. Registering an undef disables the callback.
This method registers a callback function to be invoked whenever a row is updated, inserted or deleted. Any callback set by a previous call to sqlite_update_hook is overridden. A reference to the previous callback (if any) is returned. Registering an undef disables the callback.
The callback will be called as
$code_ref->($action_code, $database, $table, $rowid)where
is an integer equal to either DBD::SQLite::INSERT, DBD::SQLite::DELETE or DBD::SQLite::UPDATE (see "Action Codes");
is the name of the database containing the affected row;
is the name of the table containing the affected row;
is the unique 64-bit signed integer key of the affected row within that table.
This method registers an authorizer callback to be invoked whenever SQL statements are being compiled by the "prepare" in DBI method. The authorizer callback should return DBD::SQLite::OK to allow the action, DBD::SQLite::IGNORE to disallow the specific action but allow the SQL statement to continue to be compiled, or DBD::SQLite::DENY to cause the entire SQL statement to be rejected with an error. If the authorizer callback returns any other value, then prepare call that triggered the authorizer will fail with an error message.
An authorizer is used when preparing SQL statements from an untrusted source, to ensure that the SQL statements do not try to access data they are not allowed to see, or that they do not try to execute malicious statements that damage the database. For example, an application may allow a user to enter arbitrary SQL queries for evaluation by a database. But the application does not want the user to be able to make arbitrary changes to the database. An authorizer could then be put in place while the user-entered SQL is being prepared that disallows everything except SELECT statements.
The callback will be called as
$code_ref->($action_code, $string1, $string2, $database, $trigger_or_view)where
is an integer that specifies what action is being authorized (see "Action Codes").
are strings that depend on the action code (see "Action Codes").
is the name of the database (main, temp, etc.) if applicable.
is the name of the inner-most trigger or view that is responsible for the access attempt, or undef if this access attempt is directly from top-level SQL code.
This method accesses the SQLite Online Backup API, and will take a backup of the named database file, copying it to, and overwriting, your current database connection. This can be particularly handy if your current connection is to the special :memory: database, and you wish to populate it from an existing DB.
This method accesses the SQLite Online Backup API, and will take a backup of the currently connected database, and write it out to the named file.
This method accesses the SQLite Online Backup API, and will take a backup of the database for the passed handle, copying it to, and overwriting, your current database connection. This can be particularly handy if your current connection is to the special :memory: database, and you wish to populate it from an existing DB. You can use this to backup from an in-memory database to another in-memory database.
This method accesses the SQLite Online Backup API, and will take a backup of the currently connected database, and write it out to the passed database handle.
Calling this method with a true value enables loading (external) SQLite3 extensions. After the call, you can load extensions like this:
$dbh->sqlite_enable_load_extension(1);
$sth = $dbh->prepare("select load_extension('libmemvfs.so')")
or die "Cannot prepare: " . $dbh->errstr();Loading an extension by a select statement (with the "load_extension" SQLite3 function like above) has some limitations. If the extension you want to use creates other functions that are not native to SQLite, use this method instead. $file (a path to the extension) is mandatory, and $proc (an entry point name) is optional. You need to call sqlite_enable_load_extension before calling sqlite_load_extension:
$dbh->sqlite_enable_load_extension(1);
$dbh->sqlite_load_extension('libsqlitefunctions.so')
or die "Cannot load extension: " . $dbh->errstr();If the extension uses SQLite mutex functions like sqlite3_mutex_enter, then the extension should be compiled with the same SQLITE_THREADSAFE compile-time setting as this module, see DBD::SQLite::compile_options().
This method registers a trace callback to be invoked whenever SQL statements are being run.
The callback will be called as
$code_ref->($statement)where
is a UTF-8 rendering of the SQL statement text as the statement first begins executing.
Additional callbacks might occur as each triggered subprogram is entered. The callbacks for triggers contain a UTF-8 SQL comment that identifies the trigger.
See also "TRACING" in DBI for better tracing options.
This method registers a profile callback to be invoked whenever a SQL statement finishes.
The callback will be called as
$code_ref->($statement, $elapsed_time)where
is the original statement text (without bind parameters).
is an estimate of wall-clock time of how long that statement took to run (in milliseconds).
This method is considered experimental and is subject to change in future versions of SQLite.
See also DBI::Profile for better profiling options.
is for internal use only.
Returns a hash reference that holds a set of status information of database connection such as cache usage. See https://www.sqlite.org/c3ref/c_dbstatus_options.html for details. You may also pass 0 as an argument to reset the status.
Returns a hash reference that holds a set of status information of SQLite statement handle such as full table scan count. See https://www.sqlite.org/c3ref/c_stmtstatus_counter.html for details. Statement status only holds the current value.
my $status = $sth->sqlite_st_status();
my $cur = $status->{fullscan_step};You may also pass 0 as an argument to reset the status.
You can change how the connected database should behave like this:
use DBD::SQLite::Constants qw/:database_connection_configuration_options/;
my $dbh = DBI->connect('dbi:SQLite::memory:');
# This disables language features that allow ordinary SQL
# to deliberately corrupt the database file
$dbh->sqlite_db_config( SQLITE_DBCONFIG_DEFENSIVE, 1 );
# This disables two-arg version of fts3_tokenizer.
$dbh->sqlite_db_config( SQLITE_DBCONFIG_ENABLE_FTS3_TOKENIZER, 0 );sqlite_db_config returns the new value after the call. If you just want to know the current value without changing anything, pass a negative integer value.
my $current_value = $dbh->sqlite_db_config( SQLITE_DBCONFIG_DEFENSIVE, -1 );As of this writing, sqlite_db_config only supports options that set an integer value. SQLITE_DBCONFIG_LOOKASIDE and SQLITE_DBCONFIG_MAINDBNAME are not supported. See also https://www.sqlite.org/capi3ref.html#sqlite3_db_config for details.
Registers a name for a virtual table module. Module names must be registered before creating a new virtual table using the module and before using a preexisting virtual table for the module. Virtual tables are explained in DBD::SQLite::VirtualTable.
Sets a new run-time limit for the category, and returns the current limit. If the new value is a negative number (or omitted), the limit is unchanged and just returns the current limit. Category ids (SQLITE_LIMIT_LENGTH, SQLITE_LIMIT_VARIABLE_NUMBER, etc) can be imported from DBD::SQLite::Constants.
Returns true if the internal SQLite connection is in an autocommit mode. This does not always return the same value as $dbh->{AutoCommit}. This returns false if you explicitly issue a <BEGIN> statement.
Returns the internal transaction status of SQLite (not of DBI). Return values (SQLITE_TXN_NONE, SQLITE_TXN_READ, SQLITE_TXN_WRITE) can be imported from DBD::SQLite::Constants. You may pass an optional schema name (usually "main"). If SQLite does not support this function, or if you pass a wrong schema name, -1 is returned.
Returns the byte offset of the start of a problematic input SQL token or -1 if the most recent error does not reference a specific token in the input SQL (or DBD::SQLite is built with an older version of SQLite).
Returns an array of compile options (available since SQLite 3.6.23, bundled in DBD::SQLite 1.30_01), or an empty array if the bundled library is old or compiled with SQLITE_OMIT_COMPILEOPTION_DIAGS.
Returns a hash reference that holds a set of status information of SQLite runtime such as memory usage or page cache usage (see https://www.sqlite.org/c3ref/c_status_malloc_count.html for details). Each of the entry contains the current value and the highwater value.
my $status = DBD::SQLite::sqlite_status();
my $cur = $status->{memory_used}{current};
my $high = $status->{memory_used}{highwater};You may also pass 0 as an argument to reset the status.
As of 1.49_05 (SQLite 3.10.0), you can use these two functions to see if a string matches a pattern. These may be useful when you create a virtual table or a custom function. See http://sqlite.org/c3ref/strlike.html and http://sqlite.org/c3ref/strglob.html for details.
A subset of SQLite C constants are made available to Perl, because they may be needed when writing hooks or authorizer callbacks. For accessing such constants, the DBD::SQLite module must be explicitly used at compile time. For example, an authorizer that forbids any DELETE operation would be written as follows :
use DBD::SQLite;
$dbh->sqlite_set_authorizer(sub {
my $action_code = shift;
return $action_code == DBD::SQLite::DELETE ? DBD::SQLite::DENY
: DBD::SQLite::OK;
});The list of constants implemented in DBD::SQLite is given below; more information can be found ad at https://www.sqlite.org/c3ref/constlist.html.
OK
DENY
IGNOREThe "set_authorizer" method registers a callback function that is invoked to authorize certain SQL statement actions. The first parameter to the callback is an integer code that specifies what action is being authorized. The second and third parameters to the callback are strings, the meaning of which varies according to the action code. Below is the list of action codes, together with their associated strings.
# constant string1 string2
# ======== ======= =======
CREATE_INDEX Index Name Table Name
CREATE_TABLE Table Name undef
CREATE_TEMP_INDEX Index Name Table Name
CREATE_TEMP_TABLE Table Name undef
CREATE_TEMP_TRIGGER Trigger Name Table Name
CREATE_TEMP_VIEW View Name undef
CREATE_TRIGGER Trigger Name Table Name
CREATE_VIEW View Name undef
DELETE Table Name undef
DROP_INDEX Index Name Table Name
DROP_TABLE Table Name undef
DROP_TEMP_INDEX Index Name Table Name
DROP_TEMP_TABLE Table Name undef
DROP_TEMP_TRIGGER Trigger Name Table Name
DROP_TEMP_VIEW View Name undef
DROP_TRIGGER Trigger Name Table Name
DROP_VIEW View Name undef
INSERT Table Name undef
PRAGMA Pragma Name 1st arg or undef
READ Table Name Column Name
SELECT undef undef
TRANSACTION Operation undef
UPDATE Table Name Column Name
ATTACH Filename undef
DETACH Database Name undef
ALTER_TABLE Database Name Table Name
REINDEX Index Name undef
ANALYZE Table Name undef
CREATE_VTABLE Table Name Module Name
DROP_VTABLE Table Name Module Name
FUNCTION undef Function Name
SAVEPOINT Operation Savepoint NameSQLite v3 provides the ability for users to supply arbitrary comparison functions, known as user-defined "collation sequences" or "collating functions", to be used for comparing two text values. https://www.sqlite.org/datatype3.html#collation explains how collations are used in various SQL expressions.
The following collation sequences are builtin within SQLite :
Compares string data using memcmp(), regardless of text encoding.
The same as binary, except the 26 upper case characters of ASCII are folded to their lower case equivalents before the comparison is performed. Note that only ASCII characters are case folded. SQLite does not attempt to do full UTF case folding due to the size of the tables required.
The same as binary, except that trailing space characters are ignored.
In addition, DBD::SQLite automatically installs the following collation sequences :
corresponds to the Perl cmp operator
Perl cmp operator, in a context where use locale is activated.
You can write for example
CREATE TABLE foo(
txt1 COLLATE perl,
txt2 COLLATE perllocale,
txt3 COLLATE nocase
)or
SELECT * FROM foo ORDER BY name COLLATE perllocaleDepending on the $dbh->{sqlite_string_mode} value, strings coming from the database and passed to the collation function may be decoded as UTF-8. This only works, though, if the sqlite_string_mode attribute is set before the first call to a perl collation sequence. The recommended way to activate unicode is to set sqlite_string_mode at connection time:
my $dbh = DBI->connect(
"dbi:SQLite:dbname=foo", "", "",
{
RaiseError => 1,
sqlite_string_mode => DBD_SQLITE_STRING_MODE_UNICODE_STRICT,
}
);The native SQLite API for adding user-defined collations is exposed through methods "sqlite_create_collation" and "sqlite_collation_needed".
To avoid calling these functions every time a $dbh handle is created, DBD::SQLite offers a simpler interface through the %DBD::SQLite::COLLATION hash : just insert your own collation functions in that hash, and whenever an unknown collation name is encountered in SQL, the appropriate collation function will be loaded on demand from the hash. For example, here is a way to sort text values regardless of their accented characters :
use DBD::SQLite;
$DBD::SQLite::COLLATION{no_accents} = sub {
my ( $a, $b ) = map lc, @_;
tr[àâáäåãçðèêéëìîíïñòôóöõøùûúüý]
[aaaaaacdeeeeiiiinoooooouuuuy] for $a, $b;
$a cmp $b;
};
my $dbh = DBI->connect("dbi:SQLite:dbname=dbfile");
my $sql = "SELECT ... FROM ... ORDER BY ... COLLATE no_accents");
my $rows = $dbh->selectall_arrayref($sql);The builtin perl or perllocale collations are predefined in that same hash.
The COLLATION hash is a global registry within the current process; hence there is a risk of undesired side-effects. Therefore, to prevent action at distance, the hash is implemented as a "write-only" hash, that will happily accept new entries, but will raise an exception if any attempt is made to override or delete a existing entry (including the builtin perl and perllocale).
If you really, really need to change or delete an entry, you can always grab the tied object underneath %DBD::SQLite::COLLATION --- but don't do that unless you really know what you are doing. Also observe that changes in the global hash will not modify existing collations in existing database handles: it will only affect new requests for collations. In other words, if you want to change the behaviour of a collation within an existing $dbh, you need to call the "create_collation" method directly.
SQLite is bundled with an extension module for full-text indexing. Tables with this feature enabled can be efficiently queried to find rows that contain one or more instances of some specified words, in any column, even if the table contains many large documents.
Explanations for using this feature are provided in a separate document: see DBD::SQLite::Fulltext_search.
The RTREE extension module within SQLite adds support for creating a R-Tree, a special index for range and multidimensional queries. This allows users to create tables that can be loaded with (as an example) geospatial data such as latitude/longitude coordinates for buildings within a city :
CREATE VIRTUAL TABLE city_buildings USING rtree(
id, -- Integer primary key
minLong, maxLong, -- Minimum and maximum longitude
minLat, maxLat -- Minimum and maximum latitude
);then query which buildings overlap or are contained within a specified region:
# IDs that are contained within query coordinates
my $contained_sql = <<"";
SELECT id FROM city_buildings
WHERE minLong >= ? AND maxLong <= ?
AND minLat >= ? AND maxLat <= ?
# ... and those that overlap query coordinates
my $overlap_sql = <<"";
SELECT id FROM city_buildings
WHERE maxLong >= ? AND minLong <= ?
AND maxLat >= ? AND minLat <= ?
my $contained = $dbh->selectcol_arrayref($contained_sql,undef,
$minLong, $maxLong, $minLat, $maxLat);
my $overlapping = $dbh->selectcol_arrayref($overlap_sql,undef,
$minLong, $maxLong, $minLat, $maxLat); For more detail, please see the SQLite R-Tree page (https://www.sqlite.org/rtree.html). Note that custom R-Tree queries using callbacks, as mentioned in the prior link, have not been implemented yet.
SQLite has a concept of "virtual tables" which look like regular tables but are implemented internally through specific functions. The fulltext or R* tree features described in the previous chapters are examples of such virtual tables, implemented in C code.
DBD::SQLite also supports virtual tables implemented in Perl code: see DBD::SQLite::VirtualTable for using or implementing such virtual tables. These can have many interesting uses for joining regular DBMS data with some other kind of data within your Perl programs. Bundled with the present distribution are :
DBD::SQLite::VirtualTable::FileContent : implements a virtual column that exposes file contents. This is especially useful in conjunction with a fulltext index; see DBD::SQLite::Fulltext_search.
DBD::SQLite::VirtualTable::PerlData : binds to a Perl array within the Perl program. This can be used for simple import/export operations, for debugging purposes, for joining data from different sources, etc.
Other Perl virtual tables may also be published separately on CPAN.
Since 1.30_01, you can retrieve the bundled SQLite C source and/or header like this:
use File::ShareDir 'dist_dir';
use File::Spec::Functions 'catfile';
# the whole sqlite3.h header
my $sqlite3_h = catfile(dist_dir('DBD-SQLite'), 'sqlite3.h');
# or only a particular header, amalgamated in sqlite3.c
my $what_i_want = 'parse.h';
my $sqlite3_c = catfile(dist_dir('DBD-SQLite'), 'sqlite3.c');
open my $fh, '<', $sqlite3_c or die $!;
my $code = do { local $/; <$fh> };
my ($parse_h) = $code =~ m{(
/\*+[ ]Begin[ ]file[ ]$what_i_want[ ]\*+
.+?
/\*+[ ]End[ ]of[ ]$what_i_want[ ]\*+/
)}sx;
open my $out, '>', $what_i_want or die $!;
print $out $parse_h;
close $out;You usually want to use this in your extension's Makefile.PL, and you may want to add DBD::SQLite to your extension's CONFIGURE_REQUIRES to ensure your extension users use the same C source/header they use to build DBD::SQLite itself (instead of the ones installed in their system).
The following items remain to be done.
Implement one or more leak detection tests that only run during AUTOMATED_TESTING and RELEASE_TESTING and validate that none of the C code we work with leaks.
Reading/writing into blobs using sqlite2_blob_open / sqlite2_blob_close.
Custom queries of a R-Tree index using a callback are possible with the SQLite C API (https://www.sqlite.org/rtree.html), so one could potentially use a callback that narrowed the result set down based on a specific need, such as querying for overlapping circles.
Bugs should be reported to GitHub issues:
https://github.com/DBD-SQLite/DBD-SQLite/issues
or via RT if you prefer:
http://rt.cpan.org/NoAuth/ReportBug.html?Queue=DBD-SQLite
Note that bugs of bundled SQLite library (i.e. bugs in sqlite3.[ch]) should be reported to the SQLite developers at sqlite.org via their bug tracker or via their mailing list.
The master repository is on GitHub:
https://github.com/DBD-SQLite/DBD-SQLite.
We also have a mailing list:
http://lists.scsys.co.uk/cgi-bin/mailman/listinfo/dbd-sqlite
Matt Sergeant <matt@sergeant.org>
Francis J. Lacoste <flacoste@logreport.org>
Wolfgang Sourdeau <wolfgang@logreport.org>
Adam Kennedy <adamk@cpan.org>
Max Maischein <corion@cpan.org>
Laurent Dami <dami@cpan.org>
Kenichi Ishigaki <ishigaki@cpan.org>
The bundled SQLite code in this distribution is Public Domain.
DBD::SQLite is copyright 2002 - 2007 Matt Sergeant.
Some parts copyright 2008 Francis J. Lacoste.
Some parts copyright 2008 Wolfgang Sourdeau.
Some parts copyright 2008 - 2013 Adam Kennedy.
Some parts copyright 2009 - 2013 Kenichi Ishigaki.
Some parts derived from DBD::SQLite::Amalgamation copyright 2008 Audrey Tang.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
The full text of the license can be found in the LICENSE file included with this module.