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Miko O'Sullivan

NAME

SQL::YASP - SQL parser and evaluater

NO LONGER BEING DEVELOPED

SQL::YASP is no longer being developed. That being said, I still think it's a pretty cool module, so I hope you'll look through it for anything you might need.

SYNOPSIS

 use SQL::YASP;
 my ($sql, $stmt, $dbrec, $params);

 $sql = <<'(SQL)';
    select 
        -- supports single and multi-line comments
        -- supports "as fieldname" format for select clauses
        first ||| last as fullname

    from members

    where
        /*
        over 100 built in SQL functions and operators
        including most MySQL functions and operators
        */
        ucase(first) ilike 'Joe' and

        -- Perl-like regular expressions
        first =~ m/ (Joe) | (Steve) /ix and

        -- handles quoted strings and escapes in quotes
        last = 'O''Sullivan' and

        -- any level of nested parens
        -- full support for placeholders
        ((rank >= ?) and (rank <= ?))
 (SQL)
 
 
 # get statement object
 $stmt = SQL::YASP::Statement->new($sql);

 # database record: populate this hash from your database
 $dbrec = 
    {
    first=>'Joe',
    last=>'Smith',
    email=>'joe@idocs.com',
    rank=>10,
    };

 # input parameters
 $params = [10, 20];

 # test if this record passes the where clause
 if ($stmt->{'where'}->evalexpr(db_record=>$dbrec, params=>$params)) {
     # get the record as indicated by the select clause
     my $retrec = $stmt->select_fields(db_record=>$dbrec);
     print $retrec->{'fullname'}, "\n";
 }

INSTALLATION

SQL::YASP can be installed with the usual routine:

    perl Makefile.PL
    make
    make test
    make install

You can also just copy Eval.pm into the SQL/ directory of one of your library trees.

A NOTE ABOUT THE STATE OF DOCUMENTATION

I'm still working on the documentaton for YASP. Documenting everything YASP does has proved a daunting task. In the spirit of Eric Raymond's motto "Release Early, Release Often" I decided to go ahead and release YASP before I finish the docs.

Sections that are not completed are noted with [*] in the title.

A GUIDED TOUR OF YASP

YASP is an SQL parser and evaluator for Perl. It parses SQL statements, allows you to discover various properties of them, and helps evaluate expressions in the statement. Let's look at some code that provides an example of the features of YASP.

    1   $sql = <<'(SQL)';
    2   select
    3      rank,
    4      first ||| last as fullname
    5   from members
    6   where first=?
    7   (SQL)
    8  
    9   $stmt = SQL::YASP->parse($sql);
    10  $dbrec = {first=>'Starflower', last=>"O'Sullivan", rank=>10};
    11  $params = ['Starflower'];
    12  
    13  if ($stmt->{'where'}->evalexpr(db_record=>$dbrec, params=>$params)) {
    14     my $calcrec = $stmt->select_fields(db_record=>$dbrec);
    15     print $calcrec->{'rank'}, "\t", $calcrec->{'fullname'}, "\n";
    16  }

Lines 1- 7 create the SQL Select statement string we're going to parse. Line 2 begins the select statement. Line 3 indicates that the rank field should be returned. Line 4 indicates that the first and last fields should be concatenated together using ||| operator (see operator documentation below), and the results should be named "fullname".

Line 5 indicates that the fields should be selected from the members table. The name of the table is given by the from property of the statement object. Line 6 gives the where clause, which will be revealed by the where clause of the statement object.

Line 9 creates statement object, passing the SQL string as the only argument. Line 10 create an anonymous hash will store data from the database. Your application can retrieve and populate this data in whatever manner you choose. Line 11 creates an anonymous array of parameters that will be used to evaluate the where clause.

Line 13 evaluates the where clause, using the database record and parameters. If the expression returns true, then 14 calls the select_fields(, again using the database record hash, to return an anonymous hash of the database fields as indicated by the expressions in the select clause. Line 15 outputs the results.

Lukasiewiczian Algebra

By default, YASP implements Lukasiewiczian algebra in evaluating SQL expressions. If you would prefer to turn off Lukasiewiczian then set the parser's lukas property to false.

Lukasiewiczian algebra is the standard in most databases such as MySql and Oracle. Lukasiewiczian algebra is a variation on Boolean Algebra invented by Jan Lukasiewicz. In Boolean algreba there are two values: true and false. Lukasiewiczian algrebra adds a third possible value: unknown, also known as null. If an expression depends on null, than the expression evaluates to null. If the expression can be determined as true or false even though it contains nulls, it returns true or false.

For example, consider the following AND expression:

    null AND true

We don't know if the expression is true because we don't know if the first argument is true. Ergo, the expression evaluates to null. However, in this expression...

    null AND false

... we know that the expression is false, because we know that the second argument is false (and therefore we know that it's not true that both arguments are true). Ergo the expression evaluates to false. In a similar way, the expression true or x evaluates to true because only one of the arguments needs to be true in an OR, and we know the first argument is true.

One of the funkiest ways that Lukasiewiczian algrebra is different from Boolean is in the NOT operator. Not true is false. Not false is true. Not null is ... null. That's because we don't know the negation of a value we don't know.

SQL COMMANDS [*]

YASP currently recognizes five SQL commands: CREATE, SELECT, DELETE, UPDATE, and INSERT. The statement object returned by the parser contains properties of the command. We'll start by looking at properties common to all types of commands, then describe properties specific to each of the commands listed above.

Each statement object has the following properties.

command (scalar)

The command being run. E.g., "select", "create", "inset"

placeholders (array)

Array of information about the placeholders in the command

placeholder_count (scalar)

how many placeholders were in the command

Now let's look at properties specific to each command.

CREATE

table_name (scalar)

Name of the object being created

create_type (scalar)

The type of object being created. Right now only "table" is handled

fields (hash)

An array of information about the fields being created. The key for each hash element is the name of the field. The hash is indexed, so each element is returned in the order it is defined in the SQL command.

Each field definition (i.e. each element in the fields hash) has two elements. "data_type" is the parsed command indicating the data type of the field. "modifiers" is an array of all other options defining the field, e.g. "unique", "undef", etc.

SELECT

where

An expression object. See the documentation for expression objects objects below.

from

This property is a hash of information about the tables from which records should be selected. The key of each element is the alias of the table if an alias is used, or the name of the table itself. The value is the name of the table. For example, this SQL command:

 select name, payment from members, registrations reg where members.id=reg.id

produces a from clause with these keys and values:

  KEY       VALUE
  reg       registrations
  members   members
fields

An indexed hash describing each field that should be returned by the select statement. The key of each hash element is the alias of the field (if an alias was given), the name of the field (if only a single field is requested, or the full expression. The value of each element is an Expression object. See the documentation for expression objects below.

DELETE

Statement objects for the DELETE command have where and from properties like SELECT statements.

UPDATE

table_name

This property holds the name of the table being updated.

set

An indexed hash describing which fields should be updated and what they should be updated to. The key of each hash element is the name of the field to be updated. The value of each element is an Expression object. See the documentation for expression objects below.

INSERT

Statement objects for the INSERT command have set and table_name properties like UPDATE statements.

EXPRESSION OBJECTS

Expression objects allow you to evaluate an SQL expression against one or more database records. Expression objects only have one public method, evalexpr, so let's get right to looking at how that method works.

Consider the following code:

 1   $sql = 'select name from members where id=?';
 2   $dbrec = { id=>10, name => 'Starflower'};
 3   $params = [10];
 4   $stmt = SQL::YASP->parse($sql);
 5   
 6   if ($stmt->{'where'}->evalexpr(db_record=>$dbrec, params=>$params))
 7       {print $dbrec->{'name'}, "\n"}

Line 1 creates an SQL statement to select the name field from the members table. Notice that the where clause uses a placeholder instead of a hardcoded values. Line 2 creates a hash reference that represents a database record. Line 3 creates an array reference that is a list of parameters that will be substituted for placeholders in the SQL statement. Line 4 creates an SQL statement object.

In Line 6 we use the expression object that is stored as the where property of the statement. We pass in the database record and the parameter list, and get back true or false.

EXTENDING YASP

YASP is designed to simplify overriding any of its functionality. Although YASP works out-of-the box, developers may want to tune it to parse and interpret specific flavors of SQL.

The Basic Concepts

The first and only required step for extending YASP is to create a new package and set its @ISA to point to YASP. Let's say you want to call you package "Extended", and that you want to put it in a file named "Extended.pm". The following code at the top of the package does the extending:

    package Extended;
    use strict;
    use SQL::YASP ':all';
    @Extended::ISA = 'SQL::YASP';

As always, be sure that the last line in Extended.pm is 1 so that you can load it into a script. You're now ready to use your new package. First, load the package:

    use Extended;

then use it to parse SQL:

    $stmt = Extended->parse($sql);

Of course, the point of extending is to change the default functionality. Generally this is done in three ways for YASP: modifying the parsing options, modifying the operators and functions, and overriding object methods.

Except for overriding methods, all of these options and properties should be set in the new function. Any of the options that are not explicitly set in new are set in after_new, which should always be called at the end of new. So, for example, suppose you wanted to remove Perl-style regexes and /* style comments. Your new function could look like this:

    sub new {
        my ($class) = @_;
        my $self = bless({}, $class);
        
        # parsing options
        $self->{'star_comments'} = 0;
        $self->{'perl_regex'} = 0;
        
        # always call after_new just before
        # returning new parser
        $self->after_new;
        
        return $self;
    }

Parsing Options

The following options can be set in the new function. See their documentation for specifics about what each property does.

    !_is_not
    backslash_escape
    dash_comments
    dquote_escape
    lukas
    perl_regex
    pound_comments
    quotes
    star_comments

DEFINING SQL OPERATORS

SQL operators are stored as a set sub references in the parser object. The parser's ops property is an array. Each element of the array is a hash, and each element of the hash is a hash of information about a specific operator. Was that a little confusing? Here's an example. Suppose we only wanted the parser to recognize four operators: =, >, *, and +. We would set the ops property in new like this:

    sub new {
        my ($class) = @_;
        my $self = bless({}, $class);
        
        # operators
        $self->{'ops'} = [
            # comparison operators
            {
            '='  => { s=>sub{$_[0] eq $_[1]} }, 
            '>' => { s=>sub{$_[0] > $_[1]} }, 
            },
            
            # mathematical operators
            {
            '*'  => { s=>sub{$_[0] eq $_[1]},  args=>ARG_NUMERIC} ,  
            '+' => { s=>sub{$_[0] > $_[1]},    args=>ARG_NUMERIC}, 
            },
        ];
        
        # always call after_new just
        # before returning new parser
        $self->after_new;
        
        return $self;
    }

Let's look at how the ops property is constructed. Each element in the array represents a level of operator precedence. Loosest bound operators are in the first element, and ops of increasingly tighter binding are in higher array elements. Operators in the same array element have equal precedence.

Each array element is itself a hash of operator definitions. The hash key is the name of operator itself. Where letters are part of the operator name, always use lowercase.

The operator definition itself is a hash of properties about the operator. Only one property is required, the s (for "sub") property. The s property should reference the subroutine that actually performs the operation. For short subs it is usually easiest to simply use an anonymous subroutine, as in the example above. By default, the subroutine receives two arguments: the value on the left and the value on the right. The sub should return whatever the result of the operation is.

In a moment we'll look at how each op function is contructed, as well as the other properties of the operator definition, but first a note about the operations that are available by default from YASP. Constructing all of your operators in a long array like above could get pretty obnoxious, especially considering that a good portion of the operators you are likely to want are already available by default from YASP. Let's suppose that you only wanted to make one change in the default operators: you want to change || from a concatenator to an or as it is in MySql. You could do that in the new function like this:

    sub new {
        my ($class) = @_;
        my $self = bless({}, $class);
        
        # get default operators
        $self->{'ops'} = SQL::YASP::default_ops();
        
        # get rid of the default || operator
        delete $self->{'ops'}->[OP_MISC]->{'||'};
        
        # alias || to or
        $self->{'ops'}->[OP_LOGICAL]->{'||'} = $self->{'ops'}->[OP_LOGICAL]->{'or'};
        
        # always call after_new just
        # before returning new parser
        $self->after_new;
        
        return $self;
    }

After blessing the object, the function sets its ops property to the default YASP operators using the SQL::YASP::default_ops() function, which returns an anonymous array of operator definitions. Next, it removes the || definition from the OP_MISC level of operators. There are six operator precedence levels in the default definitions: OP_BETWEEN, OP_LOGICAL, OP_ADD, OP_MULT, OP_EXP, and OP_MISC. The sub then redefines || into the OP_LOGICAL level, setting its definition to the same as the or operator.

Turning our attention back to the other properties of an operator definition, the other property is args, which indicates what kind of arguments the sub expects. There are four possible values. ARG_STRING (which is the default, so you can leave it out) indicates that the sub expects two strings. ARG_STRING is null-safe: YASP will send empty strings instead of spaces to such subs. If you want your operator to see nulls when they are indicated, set args to ARG_SENDNULLS. ARG_NUMERIC indicates that the sub expects numbers. For ARG_NUMERIC operators, zero will be sent instead of null.

ARG_RAW is for the situation where you don't want YASP to evaluate the expressions on the left and right of the operator, but instead to allow your sub to decide how to interpret the expressions. ARG_RAW subs receieve three arguments. The first two are anonymous arrays of the expressions to the left and right of the operator. The third argument, $opts, is a hash of values passed through the recursion of the evalexpr ("evaluate expression") sub.

To evalute one of the expressions, call evalexpr passing three value: $opts, the expression, and a variable into which the results will be stored. Contrary to what might be expected, evalexpr does not return the results of the expression when called in this manner. The results of the expression are stored in the third argument. The success of the evaulation is returned by evalexpr. If evalexpr returns false then there was a fatal error in the SQL expression (e.g. a divide by zero) and your function should proceed no further.

For example, YASP's default and operator looks like this:

    $dbin[OP_LOGICAL]{'and'}  = {args=>ARG_RAW, s=>sub{
        my ($left, $right, $opts) = @_;
        my ($val);
        
        evalexpr($left, $opts, $val) or return;
        $val or return 0;
        
        evalexpr($right, $opts, $val) or return;
        return $val;
    }};

In the first call to evalexpr passes $left, $opts, and $val. The results of the expression are stored in $val. If evalexpr returns false then the function returns, proceeding no further.

and is an ARG_RAW operator so that it short ciruits: the right expression is never evaluted if the left argument is false. That's why Cand> is an ARG_RAW operator: so that it never has to evaluate the second expression if the first is false.

If your code discovers that the expression is invalid in some way, you can throw an error to indicate that the SQL is invalid. To do so, set $SQL::YASP::err to true, set $SQL::YASP::errstr to a description of the error, and return undef from the function. For example, dividing by zero is an error, so your / operator could look like this:

    $dbin[OP_MULT]{'/'} = {args=>ARG_NUMERIC, s=>sub{
        unless ($_[1]) {
            $SQL::YASP::err = 1;
            $SQL::YASP::errstr = 'divide by zero';
            return undef;
        }
        
        $_[0] / $_[1];
    }};

Putting all of that code in your function can become burdensome, so you can also just return the results of the set_err function in a single line. set_err sets $SQL::YASP::err to true, set $SQL::YASP::errstr to its single argument, and returns undef. So, for example, the divide operator function can look like this:

    $dbin[OP_MULT]{'/'} = {args=>ARG_NUMERIC, s=>sub{
        $_[1] or return set_err('divide by zero');
        $_[0] / $_[1];
    }};

Be sure to return the results of set_err, not just call it.

A NOTE ABOUT THE NOT OPERATOR

Any operator is negated by preceding it with not. For example, our = operator above can be negated like this:

    where first not = 'Joe"

If the parser's !_is_not property is true (which it is by default), then ! can be used as an alias for not. Because ! does not require any space after it to be parsed out, we already have a not-equals operator without having to define one:

    where first != 'Joe"

Defining SQL Functions

Like operators, SQL functions are stored as a set sub references in the parser object. The parser's functions property is a hash of function definitions. Suppose, for example, that you want your parser to recognize two functions: upper, which uppercases its argument, and larger, which returns the larger of its two arguments. We would set the functions property in new like this:

    sub new {
        my ($class) = @_;
        my $self = bless({}, $class);
        
        # operators
        $self->{'functions'} = 
            {
            'upper'  => { s=>sub{uc $_[0]} },
            'larger' => { s=>sub{$_[0]>$_[1] ? $_[0] : $_[1]}}, 
            };
        
        # always call after_new just
        # before returning new parser
        $self->after_new;
        
        return $self;
    }

Each hash key is the name of the functon itself. Functions may consist of letters, numbers, and underscores, and must start with a letter. Use lowercase letters only. The value of the hash element is a function definition much like the operator definitions above. The only required property is s which references the subroutine to process the function. For short functions it is usually easiest to reference an anonymous subroutine. The args property can take the same values as for operators: ARG_STRING, ARG_RAW, ARG_NUMERIC, and ARG_SENDNULLS. For any of those type the subroutine will receive one argument: the value of the expression within the parens. There are also one other argument types for functions: ARG_NONE, which means that the function takes no arguments.

You might prefer to set your functions by grabbing a hash of all of the default functions, then adding to and deleting from the hash as needed. For example, suppose you wanted use all of the default functions, except that you want to delete the trim and reverse functions. You could do that with a new method like this:

    sub new {
        my ($class) = @_;
        my $self = bless({}, $class);
        
        # get default operators
        $self->{'functions'} = SQL::YASP::default_functions();
        
        # delete some functions we don't want
        delete $self->{'functions'}->{'trim'};
        delete $self->{'functions'}->{'reverse'};
        
        # always call after_new just
        # before returning new parser
        $self->after_new;
        
        return $self;
    }

This code loads the defaults into the functions property by calling SQL::YASP::default_functions(), which returns an anonymous hash of all the default functions. Then it simply deletes trim and reverse from the hash.

OVERRIDING OBJECT METHODS

Your extending class can override any method, but there are several methods that were particularly designed for overriding. Those methods are described in more detail in the "Overrideable Methods" section below.

PARSER OBJECT [*]

Properties [*]

ops

This property provides a set of SQL operators. See "Setting SQL Operators" for more details.

functions

This property provides a set of SQL functions. See "Setting SQL Functions" for more details.

lukas [*]
star_comments

If true, the parser recognizes comments that begin with /* and end with */. Defaults to true.

dash_comments

If true, the parser recognizes comments that begin with -- and continue for the rest of the line. Defaults to true.

pound_comments

If true, the parser recognizes comments that begin with # and continue for the rest of the line. Defaults to true.

quotes

An array of which characters are recognized as quotes. Defaults to single and double quotes. Other characters are not currently supported. This property is changed from an array to a hash in after_new().

!_is_not

If true, the parser aliases the bang (aka the exclamation point: !) to the word "not". Defaults to true.

perl_regex

If true, the parser allows Perl-style regular expressions in the SQL. For example, the following code would be allowed:

    where
        first =~ m/ (Miko) | (Starflower) /ix

Defaults to true.

keep_org_sql

If true, statement objects hold on to the original SQL string in the org_sql property. Defaults to false.

dquote_escape

If true, quotes inside quotes can be escaped by putting two quotes in a row. For example, the following expression set name to O'Sullivan:

    name='O''Sullivan'

Defaults to true.

backslash_escape

If true, quotes inside quotes can be escaped by putting a backslash in front of the quote. For example, the following expression set name to O'Sullivan:

    name='O\'Sullivan'

Defaults to true.

commands

This hash of hashes is used for specific situations where it may be ambiguous if the set of arguments is intended to be interpreted as a command or as an a field or table name. Currently, this property is only used in CREATE TABLE commands to interpret which in the list of arguments is a field name and which is a qualifier for the command.

double_word_tokens

A hash of tokens that consist of two words. Each key of the hash should be the first word of the token. The value of each element should be another hash, each key of which consists of a second word in the token, and each value of which consists of any true string. The default double_word_tokens property is created with code like this:

    $self->{'double_word_tokens'} ||= {
        primary  =>  {key=>1},
        current  =>  {date=>1},
        order    =>  {by=>1},
    };

OVERRIDEABLE METHODS [*]

new
build_tree
tree_create
tree_create_table
tree_select
tree_delete
tree_insert
tree_update
get_sections
select_fields
field_set_list

UTILITY FUNCTIONS add_args sql_split arr_split comma_split object_list get_ixhash deref_args

STATEMENT OBJECT [*]

BINARY OPERATORS

Here's a quick list of operators before we get to the full documentation:

    -
    %
    &&
    *
    /
    ^
    ||
    +
    <
    <=
    <=>
    <>
    =
    ==
    >
    >=
    and
    between
    eq
    eqi
    gt
    gti
    iin
    ilike
    in
    is
    like
    lt
    lti
    nand
    ne
    nei
    nor
    or
    xnor
    xor

-

Unary minus. Changes positive arguments to negative, negative arguments to positive.

    - 4

returns

    -4

%

Modulus. Returns the remainder from dividing the first argument by the second.

    11 % 3

returns

    2

*

Multiplication. Multiplies the numeric value of the first argument by the numeric value of the second.

    2*3

returns

    6

/

Division. Divides the numeric value of the first argument by the numeric value of the second.

    6/3

returns

    2

^

Exponentiation. Raises the numeric value of the first argument by the numeric value of the second.

    2^3

returns

    8

||

Concatenation. Returns the first argument concatenated with the second argument.

    'x' || 'y'

returns

    xy

|||

Concatenate with space in between.

    'x' ||| 'y'

returns

    x y

If either of the arguments is null then the space is not added. So, this expression

    'x' ||| null

returns a string consisting solely of 'x'. Also, the first expression must end with a non-space and the second expression must begin with a non-space, or the operator returns the strings concatenated directly without an extra space in between them.

+

Addition. Adds the numeric value of the first argument to the numeric value of the second.

    5-3

returns

    2

<

Numeric less-than. Returns true if the numeric value of the first argument is less than the numeric value of the second.

    5 < 3

returns false.

<=

Numeric less-than-or-equal-to. Returns true if the numeric value of the first argument is less than or equal to the numeric value of the second.

    3<=5

returns true.

<=>

Same as =.

<>

Numeric not-equal. Returns true if the numeric value of the first argument is not equal to the numeric value of the second.

    1 <> 0

returns true.

=

String equality. Returns true if the two arguments are identical strings.

    'Joe'='Joe'

returns true. This operator is case sensitive, so

    'Joe'='joe'

returns false. This operator does not compare numerically, so

    '1.0' = '1'

returns false. However, unquoted numbers are always normalized, so

    1.0 = 1

returns true.

==

Numeric equality. Returns true if the numeric value of the first argument is equal to the numeric value of the second.

    '1.0' == '1'

returns true.

=~

Good old fashioned Perl regular expression matches. This operator allows you to do test if a string matches using familiar regex syntax. For example:

    name =~ m/
        (Joe) |   # regexes can include Perl-style 
        (Steve)   # comments if you use the x param
        /xis

returns true if name contains the strings "Joe" or "Steve", case insensitively. Like in Perl, the x param means to ignore whitespace, the i means case-insensitive, and the s means to treat the entire expression like a single line.

>

Numeric greater-than. Returns true if the numeric value of the first argument is greater than the numeric value of the second.

    5 < 3

returns true.

>=

Numeric greater-than-or-equal-to. Returns true if the numeric value of the first argument is greater than or equal to the numeric value of the second.

    5<=3

returns true.

AND

Logical and. Identical to &&.

BETWEEN

Syntax: NumberA BETWEEN NumberB AND NumberC

Returns true if the NumberA is greater than or equal to NumberB and is also less than or equal to NumberC.

    1 between -3 and 10

returns true.

EQ

Case sensitive string equality.

    'Joe' eq 'Joe'

returns true.

EQI

Case insensitive string equality.

    'JOE' eq 'joe'

returns true.

GT

Case-sensitive string greater-than. Returns true if the first string is alphabetically after the second string.

    'pear' gt 'apple'

returns true. Because it is a case-sensitive comparison, lower-case characters are greater then upper case characters:

    'Pear' gt 'apple'

returns false.

GTI

Case-insensitive string greater-than. Returns true if the first string is alphabetically after the second string on a case-insensitive basis.

    'Pear' gti 'apple'

returns true.

IIN

Case-insensitive version of IN. See IN below.

ILIKE

Case-insensitive version of LIKE. See LIKE below.

IN

Returns true if the argument before IN is in the list of arguments after IN.

    'Joe' in 'Steve', 'Joe', 'Fred'

returns true. IN is case-sensitive. Use IIN for case-insensitivity.

IREGEXP

Case-insensitive version of REGEXP.

IS NULL, IS NOT NULL

IS NULL returns true of the preceding argument is null (that's undef to us Perl folk). An empty string is *not* null. IS NOT NULL return true if the preceding argument is not null.

LIKE

Like, y'know, returns true if the second argument can be found anywhere in the first argument.

    'Hi there Joey!' like 'there'

returns true. LIKE recognizes two special characters. _ means "any one character", and % means "zero or more of any character". So, for example, the following expression matches if NAME contains a string that begins with "J", then any one character, then "e". So "Hi Joe!", "Yo, Jae!", and "Jxe" would all match, but not "Jake".

    NAME like 'J_e'

For another example, the following expression returns true if NAME contains a string that starts with "J", then zero or more characters, then "e". So "Je", and "Yo, Jack, how are ya?" would both match:

    NAME like 'J%e'

ILIKE works just like LIKE, but is case-insensitive.

LT

String less-than.

    'apple' lt 'pear'

returns true.

LTI

Case-insensitive string less-than.

    'apple' lt 'Pear'

returns true.

NAND

Logical NAND. Returns true unless both arguments are true.

    true  nand true    -- returns false
    true  nand false   -- returns true
    false nand true    -- returns true
    false nand false   -- returns true

NE

String not-equal. Returns true if the string values of the two arguments are not the same.

    'Joe' ne 'Fred'

returns true. This function is case-sensitive.

NEI

Case-insensitive string not-equal. Returns true if the string values of the two arguments are case-insensitively not the same.

    'Joe' nei 'Fred'

returns true, whereas

    'JOE' nei 'joe'

returns false.

NOR

Logical NOR. Returns true if both arguments are false.

    true  nor true    -- returns false
    true  nor false   -- returns false
    false nor true    -- returns false
    false nor false   -- returns true

OR

Logical OR. Returns true if either of the arguments is true.

    true  or true    -- returns true
    true  or false   -- returns true
    false or true    -- returns true
    false or false   -- returns false

REGEXP

Regular expression. Returns the results of matching the first argument against the second. Uses plain old Perl regular expression syntax.

    'whatever' regexp 'e*v'

returns true. This operator is case sensitive. Use IREGEXP for a case-insensitivity.

See also the =~ operator for regexes that work like good old fashioned Perl regexes.

XNOR

Logical XNOR. Returns true if the truth of both arguments is equal.

    true  xnor true    -- returns true
    true  xnor false   -- returns false
    false xnor true    -- returns false
    false xnor false   -- returns true

XOR

Logical XOR. Returns true if the truth of both arguments is not equal.

    true  xor true    -- returns false
    true  xor false   -- returns true
    false xor true    -- returns true
    false xor false   -- returns false

FUNCTIONS [*]

I'm still working on documenting all the functions. Here's a list of implemented functions so far to tide you over until I've gotten them all properly documented.

    -
    +
    abs
    cat
    cat_ws
    ceil
    ceiling
    char
    cmp
    coalesce
    concat
    concat_ws
    crunch
    defined
    elt
    err
    false
    field
    floor
    hascontent
    hasnull
    hex
    if
    insert
    instr
    int
    isnull
    lcase
    left
    length
    load_file
    locate
    lower
    lpad
    ltrim
    mid
    mod
    not
    null
    oct
    ord
    position
    pow
    power
    repeat
    replace
    reverse
    right
    rpad
    rtrim
    sign
    soundex
    space
    square
    squared
    strcmp
    substr
    substring
    substring_index
    tcase
    title
    tolower
    totitle
    toupper
    trim
    true
    ucase
    undef
    upper

TO DO

Operators I haven't implemented yet: ascii conv bin octet_length char_length character_length bit_length

    find_in_set
    make_set
    export_set
    
    many math functions

TERMS AND CONDITIONS

Copyright (c) 2003 by Miko O'Sullivan. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. This software comes with NO WARRANTY of any kind.

AUTHOR

Miko O'Sullivan miko@idocs.com

VERSION

Version 0.10 June 12, 2003

Initial release

Version 0.11 June 28, 2003

Removed Debug::ShowStuff from module, which was only there for (as you might expect) debugging.

Version 0.12 January 2, 2015

Cleaned up test.pl. Noting that this module is no longer being developed. Noting some prerequisites. Changed CR's to Unix style. Changed encoding to UTF-8.