SQL::Parser(3)

NAME
 SQL::Parser -- validate, parse, or build SQL strings

SYNOPSIS
 use SQL::Parser;                                     # CREATE A PARSER OBJECT
 my $parser = SQL::Parser->new( $dialect, \%attrs );

 my $success = $parser->parse( $sql_string );         # PARSE A SQL STRING &
 if ($success) {                                      # DISPLAY RESULTING DATA
     use Data::Dumper;                                # STRUCTURE
     print Dumper $parser->structure;
 }

 $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

 print $parser->errstr;                               # DISPLAY CURRENT ERROR
                                                      # STRING

DESCRIPTION
 SQL::Parser is a parser, builder, and sytax validator for a
 small but useful subset of SQL (Structured Query Language).  It
 accepts SQL strings and returns either a detailed error message
 if the syntax is invalid or a data structure containing the
 results of the parse if the syntax is valid.  It will soon also
 work in reverse to build a SQL string from a supplied data
 structure.

 The module can be used in batch mode to validate a series of
 statements, or as middle-ware for DBI drivers or other related
 projects.  When combined with SQL::Statement version 0.2 or
 greater, the module can be used to actually perform the SQL
 commands on a variety of file formats using DBD::AnyData, or
 DBD::CSV, or DBD::Excel.

 The module makes use of a variety of configuration files
 located in the SQL/Dialects directory, each of which is
 essentially a simple text file listing things like supported
 data types, reserved words, and other features specific to a
 given dialect of SQL.  These features can also be turned on or
 off during program execution.

SUPPORTED SQL SYNTAX
This module is meant primarly as a base class for DBD drivers and as such concentrates on a small but useful subset of SQL 92. It does *not* in any way pretend to be a complete SQL 92 parser. The module will continue to add new supported syntax, currently, this is what is supported:

  CREATE TABLE
 CREATE [ {LOCAL|GLOBAL} TEMPORARY ] TABLE $table
        (
           $col_1 $col_type1 $col_constraints1,
           ...,
           $col_N $col_typeN $col_constraintsN,
        )
        [ ON COMMIT {DELETE|PRESERVE} ROWS ]

     * col_type must be a valid data type as defined in the
       "valid_data_types" section of the dialect file for the
       current dialect

     * col_constriaints may be "PRIMARY KEY" or one or both of
       "UNIQUE" and/or "NOT NULL"

     * IMPORTANT NOTE: temporary tables, data types and column
       constraints are checked for syntax violations but are
       currently otherwise *IGNORED* -- they are recognized by
       the parser, but not by the execution engine

     * The following valid ANSI SQL92 options are not currently
       supported: table constraints, named constraints, check
       constriants, reference constraints, constraint
       attributes, collations, default clauses, domain names as
       data types

  DROP TABLE
 DROP TABLE $table [ RESTRICT | CASCADE ]

     * IMPORTANT NOTE: drop behavior (cascade or restrict) is
       checked for valid syntax but is otherwise *IGNORED* -- it
       is recognized by the parser, but not by the execution
       engine

  INSERT INTO
 INSERT INTO $table [ ( $col1, ..., $colN ) ] VALUES ( $val1, ... $valN )

     * default values are not currently supported
     * inserting from a subquery is not currently supported

  DELETE FROM
 DELETE FROM $table [ WHERE search_condition ]

     * see "search_condition" below

  UPDATE
 UPDATE $table SET $col1 = $val1, ... $colN = $valN [ WHERE search_condition ]

     * default values are not currently supported
     * see "search_condition" below

  SELECT
      SELECT select_clause
        FROM from_clause
     [ WHERE search_condition ]
  [ ORDER BY $ocol1 [ASC|DESC], ... $ocolN [ASC|DESC] ]
     [ LIMIT [start,] length ]

      * select clause ::=
              [DISTINCT|ALL] *
           | [DISTINCT|ALL] col1 [,col2, ... colN]
           | set_function1 [,set_function2, ... set_functionN]

      * set function ::=
             COUNT ( [DISTINCT|ALL] * )
           | COUNT | MIN | MAX | AVG | SUM ( [DISTINCT|ALL] col_name )

      * from clause ::=
             table1 [, table2, ... tableN]
           | table1 NATURAL [join_type] JOIN table2
           | table1 [join_type] table2 USING (col1,col2, ... colN)
           | table1 [join_type] JOIN table2 ON table1.colA = table2.colB

      * join type ::=
             INNER
           | [OUTER] LEFT | RIGHT | FULL

      * if join_type is not specified, INNER is the default
      * if DISTINCT or ALL is not specified, ALL is the default
      * if start position is omitted from LIMIT clause, position 0 is
        the default
      * ON clauses may only contain equal comparisons and AND combiners
      * self-joins are not currently supported
      * if implicit joins are used, the WHERE clause must contain
        and equijoin condition for each table

  SEARCH CONDITION
       [NOT] $val1 $op1 $val1 [ ... AND|OR $valN $opN $valN ]

  OPERATORS
       $op  = |  <> |  < | > | <= | >=
              | IS NULL | IS NOT NULL | LIKE | CLIKE | BETWEEN | IN

  The "CLIKE" operator works exactly the same as the "LIKE"
  operator, but is case insensitive.  For example:

      WHERE foo LIKE 'bar%'   # succeeds if foo is "barbaz"
                              # fails if foo is "BARBAZ" or "Barbaz"

      WHERE foo CLIKE 'bar%'  # succeeds for "barbaz", "Barbaz", and "BARBAZ"

  STRING FUNCTIONS & MATH EXPRESSIONS
  String functions and math expressions are supported in WHERE
  clauses, in the VALUES part of an INSERT and UPDATE
  statements.  They are not currently supported in the SELECT
  statement.  For example:

    SELECT * FROM foo WHERE UPPER(bar) = 'baz'   # SUPPORTED

    SELECT UPPER(foo) FROM bar                   # NOT SUPPORTED

TRIM ( [ [LEADING|TRAILING|BOTH] ['trim_char'] FROM ] string )
    Removes all occurrences of <trim_char> from the front, back, or both sides of a string.

     BOTH is the default if neither LEADING nor TRAILING is specified.

     Space is the default if no trim_char is specified.

     Examples:

     TRIM( string )
       trims leading and trailing spaces from string

     TRIM( LEADING FROM str )
       trims leading spaces from string

     TRIM( 'x' FROM str )
       trims leading and trailing x's from string

SUBSTRING( string FROM start_pos [FOR length] )
    Returns the substring starting at start_pos and extending for "length" character or until the end of the string, if no "length" is supplied. Examples:

      SUBSTRING( 'foobar' FROM 4 )       # returns "bar"

      SUBSTRING( 'foobar' FROM 4 FOR 2)  # returns "ba"

UPPER(string) and LOWER(string)
    These return the upper-case and lower-case variants of the string:

       UPPER('foo') # returns "FOO"
       LOWER('FOO') # returns "foo"

  Identifiers (table & column names)
Regular identifiers (table and column names *without* quotes around them) are case INSENSITIVE so column foo, fOo, FOO all refer to the same column.

Delimited identifiers (table and column names *with* quotes around them) are case SENSITIVE so column "foo", "fOo", "FOO" each refer to different columns.

A delimited identifier is *never* equal to a regular identifer (so "foo" and foo are two different columns). But don't do that :-).

Remember thought that, in DBD::CSV if table names are used directly as file names, the case sensitivity depends on the OS e.g. on Windows files named foo, FOO, and fOo are the same as each other while on Unix they are different.

METHODS

  new()
The new() method creates a SQL::Parser object which can then be used to parse, validate, or build SQL strings. It takes one required parameter -- the name of the SQL dialect that will define the rules for the parser. A second optional parameter is a reference to a hash which can contain additional attributes of the parser.

 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. See the section below on the parse() method for details.

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.

For those needing backwards compatibility with SQL::Statement version 0.1x and lower, the attribute hash may also contain feature settings. See the section "FURTHER DETAILS - Backwards Compatibility" below for details.

  parse()
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 $success will be true because the strings passed to the parse() method are valid SQL strings.

In example #4, however, the value of $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 $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.

  structure()
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'
                           ]
        };

Please see the section "FURTHER DETAILS -- Parse structures" below for further examples.

  build()
This method is in progress and should be available soon.

  dialect()
 $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 $dialect_name parameter may be the name of any dialect
 configuration file on your system.  Use the
 $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.

 See the section above on "Dialects" for details of these
 configuration files.

  feature()
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.

  list()

  errstr()

FURTHER DETAILS

  Dialect Configuration Files
These will change completely when Tim finalizes the DBI get_info method.

  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.

 'SELECT make,model, FROM cars'

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

 'CREATE TABLE cars ( id INTEGER, model VARCHAR(40) )'

      column_defs => {
          id    => { data_type => INTEGER     },
          model => { data_type => VARCHAR(40) },
      },

 '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' ],

  Backwards Compatibility
This module can be used in conjunction with SQL::Statement, version 0.2 and higher. Earlier versions of SQL::Statement included a SQL::Parser as a submodule that used slightly different syntax than the current version. The current version supports all of this earlier syntax although new users are encouraged to use the new syntax listed above. If the syntax listed below is used, the module should be able to be subclassed exactly as it was with the older SQL::Statement versions and will therefore not require any modules or scripts that used it to make changes.

In the old style, features of the parser were accessed with this syntax:

 feature('create','type_blob',1); # allow BLOB as a data type
 feature('create','type_blob',0); # disallow BLOB as a data type
 feature('select','join',1);      # allow multi-table statements

The same settings could be acheieved in calls to new:

  my $parser = SQL::Parser->new(
      'Ansi',
      {
          create => {type_blob=>1},
          select => {join=>1},
      },
  );

Both of these styles of setting features are supported in the current SQL::Parser.

ACKNOWLEDGEMENTS
*Many* thanks to Ilya Sterin who wrote most of code for the
 build() method and who assisted on the parentheses parsing code
 and who proved a great deal of support, advice, and testing
 throughout the development of the module.

AUTHOR & COPYRIGHT
 This module is copyright (c) 2001 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: jeff@vpservices.com.