SQL::Parser -- validate and parse SQL strings

 use SQL::Parser;                                     # CREATE A PARSER OBJECT
 my $parser = SQL::Parser->new();

 $parser->feature( $class, $name, $value );           # SET OR FIND STATUS OF
 my $has_feature = $parser->feature( $class, $name ); # A PARSER FEATURE

 $parser->dialect( $dialect_name );                   # SET OR FIND STATUS OF
 my $current_dialect = $parser->dialect;              # A PARSER DIALECT

SQL::Parser is part of the SQL::Statement distribution and, most interaction with the parser should be done through SQL::Statement. The methods shown above create and modify a parser object. To use the parser object to parse SQL and to examine the resulting structure, you should use SQL::Statement.

Important Note: Previously SQL::Parser had its own hash-based interface for parsing, but that is now deprecated and will eventually be phased out in favor of the object-oriented parsing interface of SQL::Statement. If you are unable to transition some features to the new interface or have concerns about the phase out, please contact Jeff. See The Parse Structure for details of the now-deprecated hash method if you still need them.

Create a new parser object

 use SQL::Parser;
 my $parser = SQL::Parser->new();

The new() method creates a SQL::Parser object which can then be used to parse and validate the syntax of SQL strings. It takes two optional parameters - 1) the name of the SQL dialect that will define the syntax rules for the parser and 2) a reference to a hash which can contain additional attributes of the parser. If no dialect is specified, 'AnyData' is the default.

 use SQL::Parser;
 my $parser = SQL::Parser->new( $dialect_name, \%attrs );

The dialect_name parameter is a string containing any valid dialect such as 'ANSI', 'AnyData', or 'CSV'. See the section on the dialect() method below for details.

The attribute parameter is a reference to a hash that can contain error settings for the PrintError and RaiseError attributes.

An example:

  use SQL::Parser;
  my $parser = SQL::Parser->new('AnyData', {RaiseError=>1} );

  This creates a new parser that uses the grammar rules
  contained in the .../SQL/Dialects/AnyData.pm file and which
  sets the RaiseError attribute to true.

 $parser->dialect( $dialect_name );     # load a dialect configuration file
 my $dialect = $parser->dialect;        # get the name of the current dialect

 For example:

   $parser->dialect('AnyData');  # loads the AnyData config file
   print $parser->dialect;       # prints 'AnyData'

The CW$dialect_name parameter may be the name of any dialect configuration file on your system. Use the CW$parser->list('dialects') method to see a list of available dialects. At a minimum it will include ANSI, CSV, and AnyData. For backwards compatiblity 'Ansi' is accepted as a synonym for 'ANSI', otherwise the names are case sensitive.

Loading a new dialect configuration file erases all current parser features and resets them to those defined in the configuration file.

Features define the rules to be used by a specific parser instance. They are divided into the following classes:

    * valid_commands
    * valid_options
    * valid_comparison_operators
    * valid_data_types
    * reserved_words

Within each class a feature name is either enabled or disabled. For example, under valid_data_types the name BLOB may be either disabled or enabled. If it is not eneabled (either by being specifically disabled, or simply by not being specified at all) then any SQL string using BLOB as a data type will throw a syntax error Invalid data type: 'BLOB'.

The feature() method allows you to enable, disable, or check the status of any feature.

 $parser->feature( $class, $name, 1 );             # enable a feature

 $parser->feature( $class, $name, 0 );             # disable a feature

 my $feature = $parser->feature( $class, $name );  # show status of a feature

 For example:

 $parser->feature('reserved_words','FOO',1);       # make 'FOO' a reserved word

 $parser->feature('valid_data_types','BLOB',0);    # disallow 'BLOB' as a
                                                   # data type

                                                   # determine if the LIKE
                                                   # operator is supported
 my $LIKE = $parser->feature('valid_operators','LIKE');

See the section below on Backwards Compatibility for use of the feature() method with SQL::Statement 0.1x style parameters.

The SQL::Statement distribution can be used to either just parse SQL statements or to execute them against actual data. A broader set of syntax is supported in the parser than in the executor. For example the parser allows you to specify column constraints like PRIMARY KEY. Currently, these are ignored by the execution engine. Likewise syntax such as RESTRICT and CASCADE on DROP statements or LOCAL GLOBAL TEMPPORARY tables in CREATE are supported by the parser but ignored by the executor.

To see the list of Supported SQL syntax formerly kept in this pod, see SQL::Statement.

In the event you need to either extend or modify SQL::Parser's default behavior, the following methods may be overriden to modify the behavior: Processes the BETWEEN...AND... predicates; default converts to 2 range predicates. Process the IN (...list...) predicates; default converts to a series of OR'd '=' predicate, or AND'd '<>' predicates for NOT IN. Abstract method; default simply returns the original string. Called after get_btwn() and get_in(), but before any further predicate processing is applied. Possible uses include converting other predicate syntax not recognized by SQL::Parser into user-defined functions.

This section outlines the now-deprecated hash interface to the parsed structure. It is included for backwards compatability only. You should use the SQL::Statement object interface to the structure instead. See SQL::Statement.

Parse Structures

Here are some further examples of the data structures returned by the structure() method after a call to parse(). Only specific details are shown for each SQL instance, not the entire struture.

BIparse()

Once a SQL::Parser object has been created with the new() method, the parse() method can be used to parse any number of SQL strings. It takes a single required parameter a string containing a SQL command. The SQL string may optionally be terminated by a semicolon. The parse() method returns a true value if the parse is successful and a false value if the parse finds SQL syntax errors.

Examples:

  1) my $success = $parser->parse('SELECT * FROM foo');

  2) my $sql = 'SELECT * FROM foo';
     my $success = $parser->parse( $sql );

  3) my $success = $parser->parse(qq!
         SELECT id,phrase
           FROM foo
          WHERE id < 7
            AND phrase <> 'bar'
       ORDER BY phrase;
   !);

  4) my $success = $parser->parse('SELECT * FRoOM foo ');

In examples #1,#2, and #3, the value of CW$success will be true because the strings passed to the parse() method are valid SQL strings.

In example #4, however, the value of CW$success will be false because the string contains a SQL syntax error ('FRoOM' instead of 'FROM').

In addition to checking the return value of parse() with a variable like CW$success, you may use the PrintError and RaiseError attributes as you would in a DBI script:

 * If PrintError is true, then SQL syntax errors will be sent as
   warnings to STDERR (i.e. to the screen or to a file if STDERR
   has been redirected).  This is set to true by default which
   means that unless you specifically turn it off, all errors
   will be reported.

 * If RaiseError is true, then SQL syntax errors will cause the
   script to die, (i.e. the script will terminate unless wrapped
   in an eval).  This is set to false by default which means
   that unless you specifically turn it on, scripts will
   continue to operate even if there are SQL syntax errors.

Basically, you should leave PrintError on or else you will not be warned when an error occurs. If you are simply validating a series of strings, you will want to leave RaiseError off so that the script can check all strings regardless of whether some of them contain SQL errors. However, if you are going to try to execute the SQL or need to depend that it is correct, you should set RaiseError on so that the program will only continue to operate if all SQL strings use correct syntax.

IMPORTANT NOTE #1: The parse() method only checks syntax, it does NOT verify if the objects listed actually exist. For example, given the string SELECT model FROM cars, the parse() method will report that the string contains valid SQL but that will not tell you whether there actually is a table called cars or whether that table contains a column called 'model'. Those kinds of verifications can be performed by the SQL::Statement module, not by SQL::Parser by itself.

IMPORTANT NOTE #2: The parse() method uses rules as defined by the selected dialect configuration file and the feature() method. This means that a statement that is valid in one dialect may not be valid in another. For example the 'CSV' and 'AnyData' dialects define 'BLOB' as a valid data type but the 'ANSI' dialect does not. Therefore the statement 'CREATE TABLE foo (picture BLOB)' would be valid in the first two dialects but would produce a syntax error in the 'ANSI' dialect.

BIstructure()

After a SQL::Parser object has been created and the parse() method used to parse a SQL string, the structure() method returns the data structure of that string. This data structure may be passed on to other modules (e.g. SQL::Statement) or it may be printed out using, for example, the Data::Dumper module.

The data structure contains all of the information in the SQL string as parsed into its various components. To take a simple example:

 $parser->parse('SELECT make,model FROM cars');
 use Data::Dumper;
 print Dumper $parser->structure;

Would produce:

 $VAR1 = {
          'column_names' => [
                              'make',
                              'model'
                            ],
          'command' => 'SELECT',
          'table_names' => [
                             'cars'
                           ]
        };

 'SELECT make,model, FROM cars'

      command => 'SELECT',
      table_names => [ 'cars' ],
      column_names => [ 'make', 'model' ],

 'CREATE TABLE cars ( id INTEGER, model VARCHAR(4) )'

      column_defs => {
          id    => { data_type => INTEGER     },
          model => { data_type => VARCHAR(4) },
      },

 'SELECT DISTINCT make FROM cars'

      set_quantifier => 'DISTINCT',

 'SELECT MAX (model) FROM cars'

    set_function   => {
        name => 'MAX',
        arg  => 'models',
    },

 'SELECT * FROM cars LIMIT 5,10'

    limit_clause => {
        offset => 5,
        limit  => 10,
    },

 'SELECT * FROM vars ORDER BY make, model DESC'

    sort_spec_list => [
        { make  => 'ASC'  },
        { model => 'DESC' },
    ],

 "INSERT INTO cars VALUES ( 7, 'Chevy', 'Impala' )"

    values => [ 7, 'Chevy', 'Impala' ],

 This module is copyright (c) 2001,2005 by Jeff Zucker.
 All rights reserved.

 The module may be freely distributed under the same terms as
 Perl itself using either the "GPL License" or the "Artistic
 License" as specified in the Perl README file.

 Jeff can be reached at: jzuckerATcpan.org