SQL::Abstract(3) User Contributed Perl Documentation SQL::Abstract(3)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);
Inserting and Updating Arrays
If your database has array types (like for example Postgres), activate
the special option "array_datatypes => 1" when creating the
"SQL::Abstract" object. Then you may use an arrayref to insert and
update database array types:
my $sql = SQL::Abstract->new(array_datatypes => 1);
my %data = (
planets => [qw/Mercury Venus Earth Mars/]
);
my($stmt, @bind) = $sql->insert('solar_system', \%data);
This results in:
$stmt = "INSERT INTO solar_system (planets) VALUES (?)"
@bind = (['Mercury', 'Venus', 'Earth', 'Mars']);
Inserting and Updating SQL
In order to apply SQL functions to elements of your %data you may
specify a reference to 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) = $sql->update('people', \%data);
Notice that your %data isn't touched; the module will generate the
appropriately quirky SQL for you automatically. Usually you'll want to
specify a WHERE clause for your UPDATE, though, which is where handling
%where hashes comes in handy...
Complex where statements
This module can generate pretty complicated WHERE statements easily.
For example, simple "key=value" pairs are taken to mean equality, and
if you want to see if a field is within a set of values, you can use an
arrayref. Let's say we wanted to SELECT some data based on this
criteria:
my %where = (
requestor => 'inna',
worker => ['nwiger', 'rcwe', 'sfz'],
status => { '!=', 'completed' }
);
my($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.
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%'
Any setting other than 'lower' is ignored.
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.
sqltrue, sqlfalse
Expressions for inserting boolean values within SQL statements. By
default these are "1=1" and "1=0". They are used by the special
operators "-in" and "-not_in" for generating correct SQL even when
the argument is an empty array (see below).
logic
This determines the default logical operator for multiple WHERE
statements in arrays or hashes. If absent, the default logic is
"or" for arrays, and "and" for hashes. This means 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'
The logic can also be changed locally by inserting a modifier in
front of an arrayref :
@where = (-and => [event_date => {'>=', '2/13/99'},
event_date => {'<=', '4/24/03'} ]);
See the "WHERE CLAUSES" section for explanations.
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.
Note that if you set "bindtype" to "columns", the "\[$sql, @bind]"
construct (see "Literal SQL with placeholders and bind values
(subqueries)") will expect the bind values in this format.
quote_char
This is the character 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%'
Quoting is useful if you have tables or columns names 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
injection_guard
A regular expression "qr/.../" that is applied to any "-function"
and unquoted column name specified in a query structure. This is a
safety mechanism to avoid injection attacks when mishandling user
input e.g.:
my %condition_as_column_value_pairs = get_values_from_user();
$sqla->select( ... , \%condition_as_column_value_pairs );
If the expression matches an exception is thrown. Note that literal
SQL supplied via "\'...'" or "\['...']" is not checked in any way.
Defaults to checking for ";" and the "GO" keyword (TransactSQL)
array_datatypes
When this option is true, arrayrefs in INSERT or UPDATE are
interpreted as array datatypes and are passed directly to the DBI
layer. When this option is false, arrayrefs are interpreted as
literal SQL, just like refs to arrayrefs (but this behavior is for
backwards compatibility; when writing new queries, use the
"reference to arrayref" syntax for literal SQL).
special_ops
Takes a reference to a list of "special operators" to extend the
syntax understood by SQL::Abstract. See section "SPECIAL
OPERATORS" for details.
unary_ops
Takes a reference to a list of "unary operators" to extend the
syntax understood by SQL::Abstract. See section "UNARY OPERATORS"
for details.
insert($table, \@values || \%fieldvals, \%options)
This is the simplest function. You simply give it a table name and
either an arrayref of values or hashref of field/value pairs. It
returns an SQL INSERT statement and a list of bind values. See the
sections on "Inserting and Updating Arrays" and "Inserting and Updating
SQL" for information on how to insert with those data types.
The optional "\%options" hash reference may contain additional options
to generate the insert SQL. Currently supported options are:
returning
Takes either a scalar of raw SQL fields, or an array reference of
field names, and adds on an SQL "RETURNING" statement at the end.
This allows you to return data generated by the insert statement
(such as row IDs) without performing another "SELECT" statement.
Note, however, this is not part of the SQL standard and may not be
supported by all database engines.
update($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. See the sections on "Inserting and Updating Arrays" and
"Inserting and Updating SQL" for information on how to insert with
those data types.
select($source, $fields, $where, $order)
This returns a SQL SELECT statement and associated list of bind values,
as specified by the arguments :
$source
Specification of the 'FROM' part of the statement. The argument
can be either a plain scalar (interpreted as a table name, will be
quoted), or an arrayref (interpreted as a list of table names,
joined by commas, quoted), or a scalarref (literal table name, not
quoted), or a ref to an arrayref (list of literal table names,
joined by commas, not quoted).
$fields
Specification of the list of fields to retrieve from the source.
The argument can be either an arrayref (interpreted as a list of
field names, will be joined by commas and quoted), or a plain
scalar (literal SQL, not quoted). Please observe that this API is
not as flexible as for the first argument $table, for backwards
compatibility reasons.
$where
Optional argument to specify the WHERE part of the query. The
argument is most often a hashref, but can also be an arrayref or
plain scalar -- see section WHERE clause for details.
$order
Optional argument to specify the ORDER BY part of the query. The
argument can be a scalar, a hashref or an arrayref -- see section
ORDER BY clause for details.
delete($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');
A field associated to an empty arrayref will be considered a logical
false and will generate 0=1.
Tests for NULL values
If the value part is "undef" then this is converted to SQL <IS NULL>
my %where = (
user => 'nwiger',
status => undef,
);
becomes:
$stmt = "WHERE user = ? AND status IS NULL";
@bind = ('nwiger');
Specific 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 = ?"
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');
If you want to include literal SQL (with or without bind values), just
use a scalar reference or array reference as the value:
my %where = (
date_entered => { '>' => \["to_date(?, 'MM/DD/YYYY')", "11/26/2008"] },
date_expires => { '<' => \"now()" }
);
Which would generate:
$stmt = "WHERE date_entered > "to_date(?, 'MM/DD/YYYY') AND date_expires < now()";
@bind = ('11/26/2008');
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'} ]
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');
The reverse operator "-not_in" generates SQL "NOT IN" and is used in
the same way.
If the argument to "-in" is an empty array, 'sqlfalse' is generated (by
default : "1=0"). Similarly, "-not_in => []" generates 'sqltrue' (by
default : "1=1").
In addition to the array you can supply a chunk of literal sql or
literal sql with bind:
my %where = {
customer => { -in => \[
'SELECT cust_id FROM cust WHERE balance > ?',
2000,
],
status => { -in => \'SELECT status_codes FROM states' },
};
would generate:
$stmt = "WHERE (
customer IN ( SELECT cust_id FROM cust WHERE balance > ? )
AND status IN ( SELECT status_codes FROM states )
)";
@bind = ('2000');
Another pair of operators is "-between" and "-not_between", used with
an arrayref of two values:
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 ? )
Just like with "-in" all plausible combinations of literal SQL are
possible:
my %where = {
start0 => { -between => [ 1, 2 ] },
start1 => { -between => \["? AND ?", 1, 2] },
start2 => { -between => \"lower(x) AND upper(y)" },
start3 => { -between => [
\"lower(x)",
\["upper(?)", 'stuff' ],
] },
};
Would give you:
$stmt = "WHERE (
( start0 BETWEEN ? AND ? )
AND ( start1 BETWEEN ? AND ? )
AND ( start2 BETWEEN lower(x) AND upper(y) )
AND ( start3 BETWEEN lower(x) AND upper(?) )
)";
@bind = (1, 2, 1, 2, 'stuff');
These are the two builtin "special operators"; but the list can be
expanded : see section "SPECIAL OPERATORS" below.
Unary operators: bool
If you wish to test against boolean columns or functions within your
database you can use the "-bool" and "-not_bool" operators. For example
to test the column "is_user" being true and the column "is_enabled"
being false you would use:-
my %where = (
-bool => 'is_user',
-not_bool => 'is_enabled',
);
Would give you:
WHERE is_user AND NOT is_enabled
If a more complex combination is required, testing more conditions,
then you should use the and/or operators:-
my %where = (
-and => [
-bool => 'one',
-bool => 'two',
-bool => 'three',
-not_bool => 'four',
],
);
Would give you:
WHERE one AND two AND three AND NOT four
Nested conditions, -and/-or prefixes
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');
Clauses in hashrefs or arrayrefs can be prefixed with an "-and" or
"-or" to change the logic inside :
my @where = (
-and => [
user => 'nwiger',
[
-and => [ workhrs => {'>', 20}, geo => 'ASIA' ],
-or => { workhrs => {'<', 50}, geo => 'EURO' },
],
],
);
That would yield:
WHERE ( user = ? AND (
( workhrs > ? AND geo = ? )
OR ( workhrs < ? OR geo = ? )
) )
Algebraic inconsistency, for historical reasons
"Important note": when connecting several conditions, the "-and-"|"-or"
operator goes "outside" of the nested structure; whereas when
connecting several constraints on one column, the "-and" operator goes
"inside" the arrayref. Here is an example combining both features :
my @where = (
-and => [a => 1, b => 2],
-or => [c => 3, d => 4],
e => [-and => {-like => 'foo%'}, {-like => '%bar'} ]
)
yielding
WHERE ( ( ( a = ? AND b = ? )
OR ( c = ? OR d = ? )
OR ( e LIKE ? AND e LIKE ? ) ) )
This difference in syntax is unfortunate but must be preserved for
historical reasons. So be careful : the two examples below would seem
algebraically equivalent, but they are not
{col => [-and => {-like => 'foo%'}, {-like => '%bar'}]}
# yields : WHERE ( ( col LIKE ? AND col LIKE ? ) )
[-and => {col => {-like => 'foo%'}, {col => {-like => '%bar'}}]]
# yields : WHERE ( ( col LIKE ? OR col LIKE ? ) )
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, however using liternal SQL in this way
is deprecated - the preferred method is to use the boolean operators -
see "Unary operators: bool" :
my %where = (
priority => { '<', 2 },
is_ready => \"";
);
which yields
$stmt = "WHERE priority < ? AND is_ready";
@bind = ('2');
Literal SQL is also the only way to compare 2 columns to one another:
my %where = (
priority => { '<', 2 },
requestor => \'= submittor'
);
which creates:
$stmt = "WHERE priority < ? AND requestor = submitter";
@bind = ('2');
Literal SQL with placeholders and bind values (subqueries)
If the literal SQL to be inserted has placeholders and bind values, use
a reference to an arrayref (yes this is a double reference -- not so
common, but perfectly legal Perl). For example, to find a date in
Postgres you can use something like this:
my %where = (
date_column => \[q/= date '2008-09-30' - ?::integer/, 10/]
)
This would create:
$stmt = "WHERE ( date_column = date '2008-09-30' - ?::integer )"
@bind = ('10');
Note that you must pass the bind values in the same format as they are
returned by "where". That means that if you set "bindtype" to
"columns", you must provide the bind values in the "[ column_meta =>
value ]" format, where "column_meta" is an opaque scalar value; most
commonly the column name, but you can use any scalar value (including
references and blessed references), SQL::Abstract will simply pass it
through intact. So if "bindtype" is set to "columns" the above example
will look like:
my %where = (
date_column => \[q/= date '2008-09-30' - ?::integer/, [ dummy => 10 ]/]
)
Literal SQL is especially 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 ($sub_stmt)" => @sub_bind],
);
In the examples above, the subquery was used as an operator on a
column; but the same principle also applies for a clause within the
main %where hash, like an EXISTS subquery :
my ($sub_stmt, @sub_bind)
= $sql->select("t1", "*", {c1 => 1, c2 => \"> t0.c0"});
my %where = ( -and => [
foo => 1234,
\["EXISTS ($sub_stmt)" => @sub_bind],
]);
which yields
$stmt = "WHERE (foo = ? AND EXISTS (SELECT * FROM t1
WHERE c1 = ? AND c2 > t0.c0))";
@bind = (1234, 1);
Observe that the condition on "c2" in the subquery refers to column
"t0.c0" of the main query : this is not a bind value, so we have to
express it through a scalar ref. Writing "c2 => {">" => "t0.c0"}"
would have generated "c2 > ?" with bind value "t0.c0" ... not exactly
what we wanted here.
Finally, here is an example where a subquery is used for expressing
unary negation:
my ($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.
ORDER BY CLAUSES
Some functions take an order by clause. This can either be a scalar
(just a column name,) a hash of "{ -desc => 'col' }" or "{ -asc =>
'col' }", or an array of either of the two previous forms. Examples:
Given | Will Generate
----------------------------------------------------------
|
\'colA DESC' | ORDER BY colA DESC
|
'colA' | ORDER BY colA
|
[qw/colA colB/] | ORDER BY colA, colB
|
{-asc => 'colA'} | ORDER BY colA ASC
|
{-desc => 'colB'} | ORDER BY colB DESC
|
['colA', {-asc => 'colB'}] | ORDER BY colA, colB ASC
|
{ -asc => [qw/colA colB/] } | ORDER BY colA ASC, colB ASC
|
[ |
{ -asc => 'colA' }, | ORDER BY colA ASC, colB DESC,
{ -desc => [qw/colB/], | colC ASC, colD ASC
{ -asc => [qw/colC colD/],|
] |
===========================================================
SPECIAL OPERATORS
my $sqlmaker = SQL::Abstract->new(special_ops => [
{
regex => qr/.../,
handler => sub {
my ($self, $field, $op, $arg) = @_;
...
},
},
{
regex => qr/.../,
handler => 'method_name',
},
]);
A "special operator" is a SQL syntactic clause that can be applied to a
field, instead of a usual binary operator. For example :
WHERE field IN (?, ?, ?)
WHERE field BETWEEN ? AND ?
WHERE MATCH(field) AGAINST (?, ?)
Special operators IN and BETWEEN are fairly standard and therefore are
builtin within "SQL::Abstract" (as the overridable methods
"_where_field_IN" and "_where_field_BETWEEN"). For other operators,
like the MATCH .. AGAINST example above which is specific to MySQL, you
can write your own operator handlers - supply a "special_ops" argument
to the "new" method. That argument takes an arrayref of operator
definitions; each operator definition is a hashref with two entries:
regex
the regular expression to match the operator
handler
Either a coderef or a plain scalar method name. In both cases the
expected return is "($sql, @bind)".
When supplied with a method name, it is simply called on the "" in
SQL::Abstract object as:
$self->$method_name ($field, $op, $arg)
Where:
$op is the part that matched the handler regex
$field is the LHS of the operator
$arg is the RHS
When supplied with a coderef, it is called as:
$coderef->($self, $field, $op, $arg)
For example, here is an implementation of the MATCH .. AGAINST syntax
for MySQL
my $sqlmaker = SQL::Abstract->new(special_ops => [
# special op for MySql MATCH (field) AGAINST(word1, word2, ...)
{regex => qr/^match$/i,
handler => sub {
my ($self, $field, $op, $arg) = @_;
$arg = [$arg] if not ref $arg;
my $label = $self->_quote($field);
my ($placeholder) = $self->_convert('?');
my $placeholders = join ", ", (($placeholder) x @$arg);
my $sql = $self->_sqlcase('match') . " ($label) "
. $self->_sqlcase('against') . " ($placeholders) ";
my @bind = $self->_bindtype($field, @$arg);
return ($sql, @bind);
}
},
]);
UNARY OPERATORS
my $sqlmaker = SQL::Abstract->new(unary_ops => [
{
regex => qr/.../,
handler => sub {
my ($self, $op, $arg) = @_;
...
},
},
{
regex => qr/.../,
handler => 'method_name',
},
]);
A "unary operator" is a SQL syntactic clause that can be applied to a
field - the operator goes before the field
You can write your own operator handlers - supply a "unary_ops"
argument to the "new" method. That argument takes an arrayref of
operator definitions; each operator definition is a hashref with two
entries:
regex
the regular expression to match the operator
handler
Either a coderef or a plain scalar method name. In both cases the
expected return is $sql.
When supplied with a method name, it is simply called on the "" in
SQL::Abstract object as:
$self->$method_name ($op, $arg)
Where:
$op is the part that matched the handler regex
$arg is the RHS or argument of the operator
When supplied with a coderef, it is called as:
$coderef->($self, $op, $arg)
PERFORMANCE
Thanks to some benchmarking by Mark Stosberg, it turns out that this
module is many orders of magnitude faster than using "DBIx::Abstract".
I must admit this wasn't an intentional design issue, but it's a
byproduct of the fact that you get to control your "DBI" handles
yourself.
To maximize performance, use a code snippet like the following:
# prepare a statement handle using the first row
# and then reuse it for the rest of the rows
my($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.
However this depends on the values having the same type - if, for
example, the values of a where clause may either have values (resulting
in sql of the form "column = ?" with a single bind value), or
alternatively the values might be "undef" (resulting in sql of the form
"column IS NULL" with no bind value) then the caching technique
suggested will not work.
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 => $id});
}
Of course, you would still have to connect using "DBI" to run the
query, but the point is that if you make your form look like your
table, the actual query script can be extremely simplistic.
If you're REALLY lazy (I am), check out "HTML::QuickTable" for a fast
interface to returning and formatting data. I frequently use these
three modules together to write complex database query apps in under 50
lines.
REPO
· gitweb:
http://git.shadowcat.co.uk/gitweb/gitweb.cgi?p=dbsrgits/DBIx-Class.git
<http://git.shadowcat.co.uk/gitweb/gitweb.cgi?p=dbsrgits/DBIx-
Class.git>
· git: git://git.shadowcat.co.uk/dbsrgits/DBIx-Class.git
<git://git.shadowcat.co.uk/dbsrgits/DBIx-Class.git>
CHANGES
Version 1.50 was a major internal refactoring of "SQL::Abstract".
Great care has been taken to preserve the published behavior documented
in previous versions in the 1.* family; however, some features that
were previously undocumented, or behaved differently from the
documentation, had to be changed in order to clarify the semantics.
Hence, client code that was relying on some dark areas of
"SQL::Abstract" v1.* might behave differently in v1.50.
The main changes are :
· support for literal SQL through the "\ [$sql, bind]" syntax.
· support for the { operator => \"..." } construct (to embed literal
SQL)
· support for the { operator => \["...", @bind] } construct (to embed
literal SQL with bind values)
· optional support for array datatypes
· defensive programming : check arguments
· fixed bug with global logic, which was previously implemented
through global variables yielding side-effects. Prior versions
would interpret "[ {cond1, cond2}, [cond3, cond4] ]" as "(cond1 AND
cond2) OR (cond3 AND cond4)". Now this is interpreted as "(cond1
AND cond2) OR (cond3 OR cond4)".
· fixed semantics of _bindtype on array args
· dropped the "_anoncopy" of the %where tree. No longer necessary, we
just avoid shifting arrays within that tree.
· dropped the "_modlogic" function
ACKNOWLEDGEMENTS
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:
Ash Berlin (order_by hash term support)
Matt Trout (DBIx::Class support)
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")
Guillermo Roditi (patch to cleanup "IN" and "BETWEEN", fix and tests for _order_by)
Laurent Dami (internal refactoring, extensible list of special operators, literal SQL)
Norbert Buchmuller (support for literal SQL in hashpair, misc. fixes & tests)
Peter Rabbitson (rewrite of SQLA::Test, misc. fixes & tests)
Oliver Charles (support for "RETURNING" after "INSERT")
Thanks!
SEE ALSO
DBIx::Class, DBIx::Abstract, CGI::FormBuilder, HTML::QuickTable.
AUTHOR
Copyright (c) 2001-2007 Nathan Wiger <nwiger@cpan.org>. All Rights
Reserved.
This module is actively maintained by Matt Trout
<mst@shadowcatsystems.co.uk>
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.
LICENSE
This module is free software; you may copy this under the same terms as
perl itself (either the GNU General Public License or the Artistic
License)
perl v5.12.5 2010-12-21 SQL::Abstract(3)
