Database Name Is A File Name¶

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 <http://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.

Read-Only 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 <http://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).

DBD::SQLite And File::Temp¶

When you use File::Temp to create a temporary file/directory for SQLite databases, you need to remember:

tempfile may be locked exclusively

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);
    

CLEANUP may not work unless a database is disconnected

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.

DBD::SQLite and fork()¶

Follow the advice in the SQLite FAQ (<https://sqlite.org/faq.html>).

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.

Accessing A Database With Other Tools¶

To access the database from the command line, try using "dbish" which comes with the DBI::Shell module. Just type:

  dbish dbi:SQLite:foo.db

On 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.

Blobs¶

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 == $blob

Functions And Bind Parameters¶

As 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 three workarounds for this.

Use bind_param() explicitly

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();
    

Add zero to make it a number

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);
    

Set "sqlite_see_if_its_a_number" database handle attribute

As 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;
    

Placeholders¶

SQLite supports several placeholder expressions, including "?" and ":AAAA". Consult the DBI and SQLite documentation for details.

<http://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);

Pragma¶

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:

journal_mode

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".

legacy_file_format

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.

reverse_unordered_selects

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.

synchronous

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 <http://www.sqlite.org/pragma.html> for more details.

Foreign Keys¶

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 <http://www.sqlite.org/foreignkeys.html> for details.

Transactions¶

DBI/DBD::SQLite's transactions may be a bit confusing. They behave differently according to the status of the "AutoCommit" flag:

When the AutoCommit flag is on

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;
    

When the AutoCommit flag is off

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 mode
    

This "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>.

Transaction and Database Locking¶

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 Rollback¶

As 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;
  }

Processing Multiple Statements At A Time¶

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.

Performance¶

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 20

To 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 = OFF

Which 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.

Database Handle Attributes¶

sqlite_version

Returns the version of the SQLite library which DBD::SQLite is using, e.g., "2.8.0". Can only be read.

sqlite_unicode

If set to a true value, DBD::SQLite will turn the UTF-8 flag on for all text strings coming out of the database (this feature is currently disabled for perl < 5.8.5). For more details on the UTF-8 flag see perlunicode. The default is for the UTF-8 flag to be turned off.

Also note that due to some bizarreness in SQLite's type system (see <http://www.sqlite.org/datatype3.html>), if you want to retain blob-style behavior for some columns under "$dbh->{sqlite_unicode} = 1" (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);
  $dbh->{sqlite_unicode} = 1;
  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.

This attribute was originally named as "unicode", and renamed to "sqlite_unicode" for integrity since version 1.26_06. Old "unicode" attribute is still accessible but will be deprecated in the near future.

sqlite_allow_multiple_statements

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.

sqlite_use_immediate_transaction

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.

sqlite_see_if_its_a_number

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.

sqlite_extended_result_codes

If set to true, DBD::SQLite uses extended result codes where appropriate (see <http://www.sqlite.org/rescode.html>).

Statement Handle Attributes¶

sqlite_unprepared_statements

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.

table_info¶

  $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', 'VIEW', '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', 'VIEW', 'LOCAL TEMPORARY' or 'SYSTEM TABLE'.

primary_key, primary_key_info¶

  @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).

foreign_key_info¶

  $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          4

Default is 3 ('NO ACTION').

DELETE_RULE: The referential action for the DELETE rule. The codes are the same as for UPDATE_RULE.

Unfortunately, the DEFERRABILITY field is always "undef"; as a matter of fact, deferrability clauses are supported by SQLite, but they can't be reported because the "PRAGMA foreign_key_list" tells nothing about them.

UNIQUE_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.

statistics_info¶

  $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

ping¶

  my $bool = $dbh->ping;

returns true if the database file exists (or the database is in-memory), and the database connection is active.

$dbh->sqlite_last_insert_rowid()¶

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.

$dbh->sqlite_db_filename()¶

Retrieve the current (main) database filename. If the database is in-memory or temporary, this returns "undef".

$dbh->sqlite_busy_timeout()¶

Retrieve the current busy timeout.

$dbh->sqlite_busy_timeout( $ms )¶

Set the current busy timeout. The timeout is in milliseconds.

$dbh->sqlite_create_function( $name, $argc, $code_ref, $flags )¶

This method will register a new function which will be usable in an SQL query. The method's parameters are:

$name

The name of the function. This is the name of the function as it will be used from SQL.

$argc

The number of arguments taken by the function. If this number is -1, the function can take any number of arguments.

$code_ref

This should be a reference to the function's implementation.

$flags

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() );

REGEXP function

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.

$dbh->sqlite_create_collation( $name, $code_ref )¶

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:

$name

The name of the function exposed to SQL.

$code_ref

Reference to the function's implementation. The driver will check that this is a proper sorting function.

$dbh->sqlite_collation_needed( $code_ref )¶

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).

$dbh->sqlite_create_aggregate( $name, $argc, $pkg, $flags )¶

This method will register a new aggregate function which can then be used from SQL. The method's parameters are:

$name

The name of the aggregate function, this is the name under which the function will be available from SQL.

$argc

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.

$pkg

This is the package which implements the aggregator interface.

$flags

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:

new()

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.

step(@_)

This method will be called once for each row in the aggregate.

finalize()

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.

$dbh->sqlite_progress_handler( $n_opcodes, $code_ref )¶

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:

$n_opcodes

The progress handler is invoked once for every $n_opcodes virtual machine opcodes in SQLite.

$code_ref

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.

$dbh->sqlite_commit_hook( $code_ref )¶

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).

$dbh->sqlite_rollback_hook( $code_ref )¶

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.

$dbh->sqlite_update_hook( $code_ref )¶

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

$action_code

is an integer equal to either "DBD::SQLite::INSERT", "DBD::SQLite::DELETE" or "DBD::SQLite::UPDATE" (see "Action Codes");

$database

is the name of the database containing the affected row;

$table

is the name of the table containing the affected row;

$rowid

is the unique 64-bit signed integer key of the affected row within that table.

$dbh->sqlite_set_authorizer( $code_ref )¶

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

$action_code

is an integer that specifies what action is being authorized (see "Action Codes").

$string1, $string2

are strings that depend on the action code (see "Action Codes").

$database

is the name of the database ("main", "temp", etc.) if applicable.

$trigger_or_view

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.

$dbh->sqlite_backup_from_file( $filename )¶

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.

$dbh->sqlite_backup_to_file( $filename )¶

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.

$dbh->sqlite_enable_load_extension( $bool )¶

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('libsqlitefunctions.so')")
  or die "Cannot prepare: " . $dbh->errstr();

$dbh->sqlite_load_extension( $file, $proc )¶

Loading an extension by a select statement (with the "load_extension" SQLite3 function like above) has some limitations. If you need to, say, create other functions from an extension, use this method. $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_trace( $code_ref )¶

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

$statement

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.

$dbh->sqlite_profile( $code_ref )¶

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

$statement

is the original statement text (without bind parameters).

$elapsed_time

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.

$dbh->sqlite_table_column_metadata( $dbname, $tablename, $columnname )¶

is for internal use only.

$dbh->sqlite_db_status()¶

Returns a hash reference that holds a set of status information of database connection such as cache usage. See <http://www.sqlite.org/c3ref/c_dbstatus_options.html> for details. You may also pass 0 as an argument to reset the status.

$sth->sqlite_st_status()¶

Returns a hash reference that holds a set of status information of SQLite statement handle such as full table scan count. See <http://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.

$dbh->sqlite_create_module()¶

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.

DBD::SQLite::compile_options()¶

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.

DBD::SQLite::sqlite_status()¶

Returns a hash reference that holds a set of status information of SQLite runtime such as memory usage or page cache usage (see <http://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.

DBD::SQLite::strlike($pattern, $string, $escape_char), DBD::SQLite::strglob($pattern, $string)¶

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.

Authorizer Return Codes¶

  OK
  DENY
  IGNORE

Action Codes¶

The "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 Name

Definition¶

SQLite 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. <http://www.sqlite.org/datatype3.html#collation> explains how collations are used in various SQL expressions.

Builtin collation sequences¶

The following collation sequences are builtin within SQLite :

BINARY

Compares string data using memcmp(), regardless of text encoding.

NOCASE

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.

RTRIM

The same as binary, except that trailing space characters are ignored.

In addition, "DBD::SQLite" automatically installs the following collation sequences :

perl

corresponds to the Perl "cmp" operator

perllocale

Perl "cmp" operator, in a context where "use locale" is activated.

Usage¶

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 perllocale

Unicode handling¶

If the attribute "$dbh->{sqlite_unicode}" is set, strings coming from the database and passed to the collation function will be properly tagged with the utf8 flag; but this only works if the "sqlite_unicode" attribute is set before the first call to a perl collation sequence . The recommended way to activate unicode is to set the parameter at connection time :

  my $dbh = DBI->connect(
      "dbi:SQLite:dbname=foo", "", "",
      {
          RaiseError     => 1,
          sqlite_unicode => 1,
      }
  );

Adding user-defined collations¶

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[����������������������������]
      [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.

Leak Detection¶

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.

Stream API for Blobs¶

Reading/writing into blobs using "sqlite2_blob_open" / "sqlite2_blob_close".

Support for custom callbacks for R-Tree queries¶

Custom queries of a R-Tree index using a callback are possible with the SQLite C API (<http://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.