Nate Wiger > SQL-Abstract-1.23 > SQL::Abstract

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Module Version: 1.23   Source   Latest Release: SQL-Abstract-1.99_01

NAME ^

SQL::Abstract - Generate SQL from Perl data structures

SYNOPSIS ^

    use SQL::Abstract;

    my $sql = SQL::Abstract->new;

    my($stmt, @bind) = $sql->select($table, \@fields, \%where, \@order);

    my($stmt, @bind) = $sql->insert($table, \%fieldvals || \@values);

    my($stmt, @bind) = $sql->update($table, \%fieldvals, \%where);

    my($stmt, @bind) = $sql->delete($table, \%where);

    # Then, use these in your DBI statements
    my $sth = $dbh->prepare($stmt);
    $sth->execute(@bind);

    # Just generate the WHERE clause
    my($stmt, @bind) = $sql->where(\%where, \@order);

    # Return values in the same order, for hashed queries
    # See PERFORMANCE section for more details
    my @bind = $sql->values(\%fieldvals);

DESCRIPTION ^

This module was inspired by the excellent DBIx::Abstract. However, in using that module I found that what I really wanted to do was generate SQL, but still retain complete control over my statement handles and use the DBI interface. So, I set out to create an abstract SQL generation module.

While based on the concepts used by DBIx::Abstract, there are several important differences, especially when it comes to WHERE clauses. I have modified the concepts used to make the SQL easier to generate from Perl data structures and, IMO, more intuitive. The underlying idea is for this module to do what you mean, based on the data structures you provide it. The big advantage is that you don't have to modify your code every time your data changes, as this module figures it out.

To begin with, an SQL INSERT is as easy as just specifying a hash of key=value pairs:

    my %data = (
        name => 'Jimbo Bobson',
        phone => '123-456-7890',
        address => '42 Sister Lane',
        city => 'St. Louis',
        state => 'Louisiana',
    );

The SQL can then be generated with this:

    my($stmt, @bind) = $sql->insert('people', \%data);

Which would give you something like this:

    $stmt = "INSERT INTO people
                    (address, city, name, phone, state)
                    VALUES (?, ?, ?, ?, ?)";
    @bind = ('42 Sister Lane', 'St. Louis', 'Jimbo Bobson',
             '123-456-7890', 'Louisiana');

These are then used directly in your DBI code:

    my $sth = $dbh->prepare($stmt);
    $sth->execute(@bind);

In addition, you can apply SQL functions to elements of your %data by specifying an arrayref for the given hash value. For example, if you need to execute the Oracle to_date function on a value, you can say something like this:

    my %data = (
        name => 'Bill',
        date_entered => ["to_date(?,'MM/DD/YYYY')", "03/02/2003"],
    ); 

The first value in the array is the actual SQL. Any other values are optional and would be included in the bind values array. This gives you:

    my($stmt, @bind) = $sql->insert('people', \%data);

    $stmt = "INSERT INTO people (name, date_entered) 
                VALUES (?, to_date(?,'MM/DD/YYYY'))";
    @bind = ('Bill', '03/02/2003');

An UPDATE is just as easy, all you change is the name of the function:

    my($stmt, @bind) = $sql->update('people', \%data);

Notice that your %data isn't touched; the module will generate the appropriately quirky SQL for you automatically. Usually you'll want to specify a WHERE clause for your UPDATE, though, which is where handling %where hashes comes in handy...

This module can generate pretty complicated WHERE statements easily. For example, simple key=value pairs are taken to mean equality, and if you want to see if a field is within a set of values, you can use an arrayref. Let's say we wanted to SELECT some data based on this criteria:

    my %where = (
       requestor => 'inna',
       worker => ['nwiger', 'rcwe', 'sfz'],
       status => { '!=', 'completed' }
    );

    my($stmt, @bind) = $sql->select('tickets', '*', \%where);

The above would give you something like this:

    $stmt = "SELECT * FROM tickets WHERE
                ( requestor = ? ) AND ( status != ? )
                AND ( worker = ? OR worker = ? OR worker = ? )";
    @bind = ('inna', 'completed', 'nwiger', 'rcwe', 'sfz');

Which you could then use in DBI code like so:

    my $sth = $dbh->prepare($stmt);
    $sth->execute(@bind);

Easy, eh?

FUNCTIONS ^

The functions are simple. There's one for each major SQL operation, and a constructor you use first. The arguments are specified in a similar order to each function (table, then fields, then a where clause) to try and simplify things. Argument types are quite flexible, so whenever a hashref or arrayref is expected, you can always supply a plain scalar instead.

new(option => 'value')

The new() function takes a list of options and values, and returns a new SQL::Abstract object which can then be used to generate SQL through the methods below. The options accepted are:

case

If set to 'lower', then SQL will be generated in all lowercase. By default SQL is generated in "textbook" case meaning something like:

    SELECT a_field FROM a_table WHERE some_field LIKE '%someval%'
cmp

This determines what the default comparison operator is. By default it is =, meaning that a hash like this:

    %where = (name => 'nwiger', email => 'nate@wiger.org');

Will generate SQL like this:

    WHERE name = 'nwiger' AND email = 'nate@wiger.org'

However, you may want loose comparisons by default, so if you set cmp to like you would get SQL such as:

    WHERE name like 'nwiger' AND email like 'nate@wiger.org'

You can also override the comparsion on an individual basis - see the huge section on "WHERE CLAUSES" at the bottom.

logic

This determines the default logical operator for multiple WHERE statements in arrays. By default it is "or", meaning that a WHERE array of the form:

    @where = (
        event_date => {'>=', '2/13/99'}, 
        event_date => {'<=', '4/24/03'}, 
    );

Will generate SQL like this:

    WHERE event_date >= '2/13/99' OR event_date <= '4/24/03'

This is probably not what you want given this query, though (look at the dates). To change the "OR" to an "AND", simply specify:

    my $sql = SQL::Abstract->new(logic => 'and');

Which will change the above WHERE to:

    WHERE event_date >= '2/13/99' AND event_date <= '4/24/03'
convert

This will automatically convert comparisons using the specified SQL function for both column and value. This is mostly used with an argument of upper or lower, so that the SQL will have the effect of case-insensitive "searches". For example, this:

    $sql = SQL::Abstract->new(convert => 'upper');
    %where = (keywords => 'MaKe iT CAse inSeNSItive');

Will turn out the following SQL:

    WHERE upper(keywords) like upper('MaKe iT CAse inSeNSItive')

The conversion can be upper(), lower(), or any other SQL function that can be applied symmetrically to fields (actually SQL::Abstract does not validate this option; it will just pass through what you specify verbatim).

bindtype

This is a kludge because many databases suck. For example, you can't just bind values using DBI's execute() for Oracle CLOB or BLOB fields. Instead, you have to use bind_param():

    $sth->bind_param(1, 'reg data');
    $sth->bind_param(2, $lots, {ora_type => ORA_CLOB});

The problem is, SQL::Abstract will normally just return a @bind array, which loses track of which field each slot refers to. Fear not.

If you specify bindtype in new, you can determine how @bind is returned. Currently, you can specify either normal (default) or columns. If you specify columns, you will get an array that looks like this:

    my $sql = SQL::Abstract->new(bindtype => 'columns');
    my($stmt, @bind) = $sql->insert(...);

    @bind = (
        [ 'column1', 'value1' ],
        [ 'column2', 'value2' ],
        [ 'column3', 'value3' ],
    );

You can then iterate through this manually, using DBI's bind_param().

    $sth->prepare($stmt);
    my $i = 1;
    for (@bind) {
        my($col, $data) = @$_;
        if ($col eq 'details' || $col eq 'comments') {
            $sth->bind_param($i, $data, {ora_type => ORA_CLOB});
        } elsif ($col eq 'image') {
            $sth->bind_param($i, $data, {ora_type => ORA_BLOB});
        } else {
            $sth->bind_param($i, $data);
        }
        $i++;
    }
    $sth->execute;      # execute without @bind now

Now, why would you still use SQL::Abstract if you have to do this crap? Basically, the advantage is still that you don't have to care which fields are or are not included. You could wrap that above for loop in a simple sub called bind_fields() or something and reuse it repeatedly. You still get a layer of abstraction over manual SQL specification.

quote_char

This is the character or characters that a table or column name will be quoted with. By default this is an empty string, but you could set it to the character `, to generate SQL like this:

  SELECT `a_field` FROM `a_table` WHERE `some_field` LIKE '%someval%'

Alternatively, you can supply an array ref of two items, the first being the left hand quote character, and the second the right hand quote character. For example, you could supply ['[',']'] for SQL Server 2000 compliant quotes that generates SQL like this:

  SELECT [a_field] FROM [a_table] WHERE [some_field] LIKE '%someval%'

This is useful if you have tables or columns that are reserved words in your database's SQL dialect.

name_sep

This is the character that separates a table and column name. It is necessary to specify this when the quote_char option is selected, so that tables and column names can be individually quoted like this:

  SELECT `table`.`one_field` FROM `table` WHERE `table`.`other_field` = 1

insert($table, \@values || \%fieldvals)

This is the simplest function. You simply give it a table name and either an arrayref of values or hashref of field/value pairs. It returns an SQL INSERT statement and a list of bind values.

update($table, \%fieldvals, \%where)

This takes a table, hashref of field/value pairs, and an optional hashref WHERE clause. It returns an SQL UPDATE function and a list of bind values.

select($table, \@fields, \%where, \@order)

This takes a table (or arrayref of tables), arrayref of fields (or '*'), optional hashref WHERE clause, and optional arrayref order by, and returns the corresponding SQL SELECT statement and list of bind values.

Columns in @order may be prefixed by a '+' or '-' sign, meaning "ascending" or "descending". Hence

  select("customers", "*", {}, [qw/-balance +name/])

means

  SELECT * FROM customers ORDER BY balance DESC, name ASC

delete($table, \%where)

This takes a table name and optional hashref WHERE clause. It returns an SQL DELETE statement and list of bind values.

where(\%where, \@order)

This is used to generate just the WHERE clause. For example, if you have an arbitrary data structure and know what the rest of your SQL is going to look like, but want an easy way to produce a WHERE clause, use this. It returns an SQL WHERE clause and list of bind values.

values(\%data)

This just returns the values from the hash %data, in the same order that would be returned from any of the other above queries. Using this allows you to markedly speed up your queries if you are affecting lots of rows. See below under the "PERFORMANCE" section.

generate($any, 'number', $of, \@data, $struct, \%types)

Warning: This is an experimental method and subject to change.

This returns arbitrarily generated SQL. It's a really basic shortcut. It will return two different things, depending on return context:

    my($stmt, @bind) = $sql->generate('create table', \$table, \@fields);
    my $stmt_and_val = $sql->generate('create table', \$table, \@fields);

These would return the following:

    # First calling form
    $stmt = "CREATE TABLE test (?, ?)";
    @bind = (field1, field2);

    # Second calling form
    $stmt_and_val = "CREATE TABLE test (field1, field2)";

Depending on what you're trying to do, it's up to you to choose the correct format. In this example, the second form is what you would want.

By the same token:

    $sql->generate('alter session', { nls_date_format => 'MM/YY' });

Might give you:

    ALTER SESSION SET nls_date_format = 'MM/YY'

You get the idea. Strings get their case twiddled, but everything else remains verbatim.

WHERE CLAUSES ^

Introduction

This module uses a variation on the idea from DBIx::Abstract. It is NOT, repeat not 100% compatible. The main logic of this module is that things in arrays are OR'ed, and things in hashes are AND'ed.

The easiest way to explain is to show lots of examples. After each %where hash shown, it is assumed you used:

    my($stmt, @bind) = $sql->where(\%where);

However, note that the %where hash can be used directly in any of the other functions as well, as described above.

Key-value pairs

So, let's get started. To begin, a simple hash:

    my %where  = (
        user   => 'nwiger',
        status => 'completed'
    );

Is converted to SQL key = val statements:

    $stmt = "WHERE user = ? AND status = ?";
    @bind = ('nwiger', 'completed');

One common thing I end up doing is having a list of values that a field can be in. To do this, simply specify a list inside of an arrayref:

    my %where  = (
        user   => 'nwiger',
        status => ['assigned', 'in-progress', 'pending'];
    );

This simple code will create the following:

    $stmt = "WHERE user = ? AND ( status = ? OR status = ? OR status = ? )";
    @bind = ('nwiger', 'assigned', 'in-progress', 'pending');

Comparison operators

If you want to specify a different type of operator for your comparison, you can use a hashref for a given column:

    my %where  = (
        user   => 'nwiger',
        status => { '!=', 'completed' }
    );

Which would generate:

    $stmt = "WHERE user = ? AND status != ?";
    @bind = ('nwiger', 'completed');

To test against multiple values, just enclose the values in an arrayref:

    status => { '!=', ['assigned', 'in-progress', 'pending'] };

Which would give you:

    "WHERE status != ? OR status != ? OR status != ?"

But, this is probably not what you want in this case (look at it). So the hashref can also contain multiple pairs, in which case it is expanded into an AND of its elements:

    my %where  = (
        user   => 'nwiger',
        status => { '!=', 'completed', -not_like => 'pending%' }
    );

    # Or more dynamically, like from a form
    $where{user} = 'nwiger';
    $where{status}{'!='} = 'completed';
    $where{status}{'-not_like'} = 'pending%';

    # Both generate this
    $stmt = "WHERE user = ? AND status != ? AND status NOT LIKE ?";
    @bind = ('nwiger', 'completed', 'pending%');

To get an OR instead, you can combine it with the arrayref idea:

    my %where => (
         user => 'nwiger',
         priority => [ {'=', 2}, {'!=', 1} ]
    );

Which would generate:

    $stmt = "WHERE user = ? AND priority = ? OR priority != ?";
    @bind = ('nwiger', '2', '1');

Logic and nesting operators

In the example above, there is a subtle trap if you want to say something like this (notice the AND):

    WHERE priority != ? AND priority != ?

Because, in Perl you can't do this:

    priority => { '!=', 2, '!=', 1 }

As the second != key will obliterate the first. The solution is to use the special -modifier form inside an arrayref:

    priority => [ -and => {'!=', 2}, {'!=', 1} ]

Normally, these would be joined by OR, but the modifier tells it to use AND instead. (Hint: You can use this in conjunction with the logic option to new() in order to change the way your queries work by default.) Important: Note that the -modifier goes INSIDE the arrayref, as an extra first element. This will NOT do what you think it might:

    priority => -and => [{'!=', 2}, {'!=', 1}]   # WRONG!

Here is a quick list of equivalencies, since there is some overlap:

    # Same
    status => {'!=', 'completed', 'not like', 'pending%' }
    status => [ -and => {'!=', 'completed'}, {'not like', 'pending%'}]

    # Same
    status => {'=', ['assigned', 'in-progress']}
    status => [ -or => {'=', 'assigned'}, {'=', 'in-progress'}]
    status => [ {'=', 'assigned'}, {'=', 'in-progress'} ]

In addition to -and and -or, there is also a special -nest operator which adds an additional set of parens, to create a subquery. For example, to get something like this:

    $stmt = WHERE user = ? AND ( workhrs > ? OR geo = ? )
    @bind = ('nwiger', '20', 'ASIA');

You would do:

    my %where = (
         user => 'nwiger',
        -nest => [ workhrs => {'>', 20}, geo => 'ASIA' ],
    );

Special operators : IN, BETWEEN, etc.

You can also use the hashref format to compare a list of fields using the IN comparison operator, by specifying the list as an arrayref:

    my %where  = (
        status   => 'completed',
        reportid => { -in => [567, 2335, 2] }
    );

Which would generate:

    $stmt = "WHERE status = ? AND reportid IN (?,?,?)";
    @bind = ('completed', '567', '2335', '2');

You can use this same format to use other grouping functions, such as BETWEEN, SOME, and so forth. For example:

    my %where  = (
        user   => 'nwiger',
        completion_date => {
           -not_between => ['2002-10-01', '2003-02-06']
        }
    );

Would give you:

    WHERE user = ? AND completion_date NOT BETWEEN ( ? AND ? )

Nested conditions

So far, we've seen how multiple conditions are joined with a top-level AND. We can change this by putting the different conditions we want in hashes and then putting those hashes in an array. For example:

    my @where = (
        {
            user   => 'nwiger',
            status => { -like => ['pending%', 'dispatched'] },
        },
        {
            user   => 'robot',
            status => 'unassigned',
        }
    );

This data structure would create the following:

    $stmt = "WHERE ( user = ? AND ( status LIKE ? OR status LIKE ? ) )
                OR ( user = ? AND status = ? ) )";
    @bind = ('nwiger', 'pending', 'dispatched', 'robot', 'unassigned');

This can be combined with the -nest operator to properly group SQL statements:

    my @where = (
         -and => [
            user => 'nwiger',
            -nest => [
                -and => [workhrs => {'>', 20}, geo => 'ASIA' ],
                -and => [workhrs => {'<', 50}, geo => 'EURO' ]
            ],
        ],
    );

That would yield:

    WHERE ( user = ? AND 
          ( ( workhrs > ? AND geo = ? )
         OR ( workhrs < ? AND geo = ? ) ) )

Literal SQL

Finally, sometimes only literal SQL will do. If you want to include literal SQL verbatim, you can specify it as a scalar reference, namely:

    my $inn = 'is Not Null';
    my %where = (
        priority => { '<', 2 },
        requestor => \$inn
    );

This would create:

    $stmt = "WHERE priority < ? AND requestor is Not Null";
    @bind = ('2');

Note that in this example, you only get one bind parameter back, since the verbatim SQL is passed as part of the statement.

Of course, just to prove a point, the above can also be accomplished with this:

    my %where = (
        priority  => { '<', 2 },
        requestor => { '!=', undef },
    );

TMTOWTDI.

Conditions on boolean columns can be expressed in the same way, passing a reference to an empty string :

    my %where = (
        priority  => { '<', 2 },
        is_ready  => \"";
    );

which yields

    $stmt = "WHERE priority < ? AND is_ready";
    @bind = ('2');

Nested queries

A key-value pair in a hash is interpreted as a subquery whenever the key contains n question marks (n > 0), and the value is an arrayref of length n. In that case, the statement is just inserted as is in the final statement, and the bind values are pushed unto the final bind values. This is useful for nesting parenthesized clauses in the main SQL query.

Here is a first example :

  my ($sub_stmt, @sub_bind) = ("SELECT c1 FROM t1 WHERE c2 < ? AND c3 LIKE ?",
                               100, "foo%");
  my %where = (
    foo => 1234,
    bar => {"IN ($sub_stmt)" => \@sub_bind},
  );

This yields :

  $stmt = "WHERE (foo = ? AND bar IN (SELECT c1 FROM t1 
                                             WHERE c2 < ? AND c3 LIKE ?))";
  @bind = (1234, 100, "foo%");

Other subquery operators, like for example "> ALL" or "NOT IN", are expressed in the same way. Of course the $sub_stmt and its associated bind values can be generated through a former call to select() :

  my ($sub_stmt, @sub_bind)
     = $sql->select("t1", "c1", {c2 => {"<" => 100}, 
                                 c3 => {-like => "foo%"}});
  my %where = (
    foo => 1234,
    bar => {"> ALL ($sub_stmt)" => \@sub_bind},
  );

In the examples above, the subquery was used as an operator on a column; but the same principle also applies for an EXISTS subquery within the main %where hash :

  my ($sub_stmt, @sub_bind) 
     = $sql->select("t1", "*", {c1 => 1, c2 => \"> t0.c0"});
  my %where = (
    foo                  => 1234,
    "EXISTS ($sub_stmt)" => \@sub_bind,
  );

which yields

  $stmt = "WHERE (foo = ? AND EXISTS (SELECT * FROM t1 
                                        WHERE c1 = ? AND c2 > t0.c0))";
  @bind = (1234, 1);

Observe that the condition on c2 in the subquery refers to column t0.c0 of the main query : this is not a bind value, so we have to express it through a scalar ref. Writing c2 => {">" => "t0.c0"} would have generated c2 > ? with bind value "t0.c0" ... not exactly what we wanted here.

Another use of the subquery technique is when some SQL clauses need parentheses, as it often occurs with some proprietary SQL extensions like for example fulltext expressions, geospatial expressions, NATIVE clauses, etc. Here is an example of a fulltext query in MySQL :

  my %where = (
    "MATCH (col1, col2) AGAINST (?)" => ["apples"]
  );

Observe that the value "apples" is not a plain scalar : it needs to be within an arrayref of size 1, in order to match the single question mark on the left-hand side.

Finally, here is an example where a subquery is used for expressing unary negation:

  my ($sub_stmt, @sub_bind) 
     = $sql->where({age => [{"<" => 10}, {">" => 20}]});
  $sub_stmt =~ s/^ where //i; # don't want "WHERE" in the subclause
  my %where = (
        lname             => {like => '%son%'},
        "NOT ($sub_stmt)" => \@sub_bind,
    );

This yields

  $stmt = "lname LIKE ? AND NOT ( age < ? OR age > ? )"
  @bind = ('%son%', 10, 20)

Conclusion

These pages could go on for a while, since the nesting of the data structures this module can handle are pretty much unlimited (the module implements the WHERE expansion as a recursive function internally). Your best bet is to "play around" with the module a little to see how the data structures behave, and choose the best format for your data based on that.

And of course, all the values above will probably be replaced with variables gotten from forms or the command line. After all, if you knew everything ahead of time, you wouldn't have to worry about dynamically-generating SQL and could just hardwire it into your script.

PERFORMANCE ^

Thanks to some benchmarking by Mark Stosberg, it turns out that this module is many orders of magnitude faster than using DBIx::Abstract. I must admit this wasn't an intentional design issue, but it's a byproduct of the fact that you get to control your DBI handles yourself.

To maximize performance, use a code snippet like the following:

    # prepare a statement handle using the first row
    # and then reuse it for the rest of the rows
    my($sth, $stmt);
    for my $href (@array_of_hashrefs) {
        $stmt ||= $sql->insert('table', $href);
        $sth  ||= $dbh->prepare($stmt);
        $sth->execute($sql->values($href));
    }

The reason this works is because the keys in your $href are sorted internally by SQL::Abstract. Thus, as long as your data retains the same structure, you only have to generate the SQL the first time around. On subsequent queries, simply use the values function provided by this module to return your values in the correct order.

FORMBUILDER ^

If you use my CGI::FormBuilder module at all, you'll hopefully really like this part (I do, at least). Building up a complex query can be as simple as the following:

    #!/usr/bin/perl

    use CGI::FormBuilder;
    use SQL::Abstract;

    my $form = CGI::FormBuilder->new(...);
    my $sql  = SQL::Abstract->new;

    if ($form->submitted) {
        my $field = $form->field;
        my $id = delete $field->{id};
        my($stmt, @bind) = $sql->update('table', $field, {id => $id});
    }

Of course, you would still have to connect using DBI to run the query, but the point is that if you make your form look like your table, the actual query script can be extremely simplistic.

If you're REALLY lazy (I am), check out HTML::QuickTable for a fast interface to returning and formatting data. I frequently use these three modules together to write complex database query apps in under 50 lines.

CONTRIBUTORS ^

There are a number of individuals that have really helped out with this module. Unfortunately, most of them submitted bugs via CPAN so I have no idea who they are! But the people I do know are:

    Mark Stosberg (benchmarking)
    Chas Owens (initial "IN" operator support)
    Philip Collins (per-field SQL functions)
    Eric Kolve (hashref "AND" support)
    Mike Fragassi (enhancements to "BETWEEN" and "LIKE")
    Dan Kubb (support for "quote_char" and "name_sep")
    Matt Trout (DBIx::Class support)
    Laurent Dami (large patch for +/- support and subqueries)
    Robbie Bow (patch to for "quote_char" to fix MQ SQL Server)

Thanks!

BUGS ^

If found, please DO NOT submit anything via rt.cpan.org - that just causes me a ton of work. Email me a patch (or script demonstrating the problem) to the below address, and include the VERSION you're using.

SEE ALSO ^

DBIx::Abstract, DBI, CGI::FormBuilder, HTML::QuickTable

AUTHOR ^

Copyright (c) 2001-2006 Nathan Wiger <nwiger@cpan.org>. All Rights Reserved.

For support, your best bet is to try the DBIx::Class users mailing list. While not an official support venue, DBIx::Class makes heavy use of SQL::Abstract, and as such list members there are very familiar with how to create queries.

This module is free software; you may copy this under the terms of the GNU General Public License, or the Artistic License, copies of which should have accompanied your Perl kit.

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