SQL::Statement::FunctiUser3Contributed Perl DocumeSQL::Statement::Functions(3)NAMESQL::Statement::Functions - built-in & user-defined SQL functions
SYNOPSIS
SELECT Func(args);
SELECT * FROM Func(args);
SELECT * FROM x WHERE Funcs(args);
SELECT * FROM x WHERE y < Funcs(args);
DESCRIPTION
This module contains the built-in functions for SQL::Parser and
SQL::Statement. All of the functions are also available in any DBDs
that subclass those modules (e.g. DBD::CSV, DBD::DBM, DBD::File,
DBD::AnyData, DBD::Excel, etc.).
This documentation covers built-in functions and also explains how to
create your own functions to supplement the built-in ones. It's easy.
If you create one that is generally useful, see below for how to submit
it to become a built-in function.
Function syntax
When using SQL::Statement/SQL::Parser directly to parse SQL, functions
(either built-in or user-defined) may occur anywhere in a SQL statement
that values, column names, table names, or predicates may occur. When
using the modules through a DBD or in any other context in which the
SQL is both parsed and executed, functions can occur in the same places
except that they can not occur in the column selection clause of a
SELECT statement that contains a FROM clause.
# valid for both parsing and executing
SELECT MyFunc(args);
SELECT * FROM MyFunc(args);
SELECT * FROM x WHERE MyFuncs(args);
SELECT * FROM x WHERE y < MyFuncs(args);
# valid only for parsing (won't work from a DBD)
SELECT MyFunc(args) FROM x WHERE y;
User-Defined Functions
Loading User-Defined Functions
In addition to the built-in functions, you can create any number of
your own user-defined functions (UDFs). In order to use a UDF in a
script, you first have to create a perl subroutine (see below), then
you need to make the function available to your database handle with
the CREATE FUNCTION or LOAD commands:
# load a single function "foo" from a subroutine
# named "foo" in the current package
$dbh->do(" CREATE FUNCTION foo EXTERNAL ");
# load a single function "foo" from a subroutine
# named "bar" in the current package
$dbh->do(" CREATE FUNCTION foo EXTERNAL NAME bar");
# load a single function "foo" from a subroutine named "foo"
# in another package
$dbh->do(' CREATE FUNCTION foo EXTERNAL NAME "Bar::Baz::foo" ');
# load all the functions in another package
$dbh->do(' LOAD "Bar::Baz" ');
Functions themselves should follow SQL identifier naming rules.
Subroutines loaded with CREATE FUNCTION can have any valid perl
subroutine name. Subroutines loaded with LOAD must start with
SQL_FUNCTION_ and then the actual function name. For example:
package Qux::Quimble;
sub SQL_FUNCTION_FOO { ... }
sub SQL_FUNCTION_BAR { ... }
sub some_other_perl_subroutine_not_a_function { ... }
1;
# in another package
$dbh->do("LOAD Qux::Quimble");
# This loads FOO and BAR as SQL functions.
Creating User-Defined Functions
User-defined functions (UDFs) are perl subroutines that return values
appropriate to the context of the function in a SQL statement. For
example the built-in CURRENT_TIME returns a string value and therefore
may be used anywhere in a SQL statement that a string value can. Here'
the entire perl code for the function:
# CURRENT_TIME
#
# arguments : none
# returns : string containing current time as hh::mm::ss
#
sub SQL_FUNCTION_CURRENT_TIME {
sprintf "%02s::%02s::%02s",(localtime)[2,1,0]
}
More complex functions can make use of a number of arguments always
passed to functions automatically. Functions always receive these
values in @_:
sub FOO {
my($self,$sth,$rowhash,@params);
}
The first argument, $self, is whatever class the function is defined
in, not generally useful unless you have an entire module to support
the function.
The second argument, $sth is the active statement handle of the current
statement. Like all active statement handles it contains the current
database handle in the {Database} attribute so you can have access to
the database handle in any function:
sub FOO {
my($self,$sth,$rowhash,@params);
my $dbh = $sth->{Database};
# $dbh->do( ...), etc.
}
In actual practice you probably want to use $sth-{Database} directly
rather than making a local copy, so $sth->{Database}->do(...).
The third argument, $rowhash, is a reference to a hash containing the
key/value pairs for the current database row the SQL is searching.
This isn't relevant for something like CURRENT_TIME which isn't based
on a SQL search, but here's an example of a (rather useless) UDF using
$rowhash that just joins the values for the entire row with a colon:
sub COLON_JOIN {
my($self,$sth,$rowhash,@params);
my $str = join ':', values %$rowhash;
}
The remaining arguments, @params, are arguments passed by users to the
function, either directly or with placeholders; another silly example
which just returns the results of multiplying the arguments passed to
it:
sub MULTIPLY {
my($self,$sth,$rowhash,@params);
return $params[0] * $params[1];
}
# first make the function available
#
$dbh->do("CREATE FUNCTION MULTIPLY");
# then multiply col3 in each row times seven
#
my $sth=$dbh->prepare("SELECT col1 FROM tbl1 WHERE col2 = MULTIPLY(col3,7)");
$sth->execute;
#
# or
#
my $sth=$dbh->prepare("SELECT col1 FROM tbl1 WHERE col2 = MULTIPLY(col3,?)");
$sth->execute(7);
Creating In-Memory Tables with functions
A function can return almost anything, as long is it is an appropriate
return for the context the function will be used in. In the special
case of table-returning functions, the function should return a
reference to an array of array references with the first row being the
column names and the remaining rows the data. For example:
1. create a function that returns an AoA,
sub Japh {[
[qw( id word )],
[qw( 1 Hacker )],
[qw( 2 Perl )],
[qw( 3 Another )],
[qw( 4 Just )],
]}
2. make your database handle aware of the function
$dbh->do("CREATE FUNCTION 'Japh');
3. Access the data in the AoA from SQL
$sth = $dbh->prepare("SELECT word FROM Japh ORDER BY id DESC");
Or here's an example that does a join on two in-memory tables:
sub Prof {[ [qw(pid pname)],[qw(1 Sue )],[qw(2 Bob)],[qw(3 Tom )] ]}
sub Class {[ [qw(pid cname)],[qw(1 Chem)],[qw(2 Bio)],[qw(2 Math)] ]}
$dbh->do("CREATE FUNCTION $_) for qw(Prof Class);
$sth = $dbh->prepare("SELECT * FROM Prof NATURAL JOIN Class");
The "Prof" and "Class" functions return tables which can be used like
any SQL table.
More complex functions might do something like scrape an RSS feed, or
search a file system and put the results in AoA. For example, to
search a directory with SQL:
sub Dir {
my($self,$sth,$rowhash,$dir)=@_;
opendir D, $dir or die "'$dir':$!";
my @files = readdir D;
my $data = [[qw(fileName fileExt)]];
for (@files) {
my($fn,$ext) = /^(.*)(\.[^\.]+)$/;
push @$data, [$fn,$ext];
}
return $data;
}
$dbh->do("CREATE FUNCTION Dir");
printf "%s\n", join' ',@{ $dbh->selectcol_arrayref("
SELECT fileName FROM Dir('./') WHERE fileExt = '.pl'
")};
Obviously, that function could be expanded with File::Find and/or stat
to provide more information and it could be made to accept a list of
directories rather than a single directory.
Table-Returning functions are a way to turn *anything* that can be
modeled as an AoA into a DBI data source.
Built-in Functions
Aggregate Functions
min, max, avg, sum, count
Aggregate functions are handled elsewhere, see SQL::Parser for
documentation.
Date and Time Functions
current_date, current_time, current_timestamp
CURRENT_DATE
# purpose : find current date
# arguments : none
# returns : string containing current date as yyyy-mm-dd
CURRENT_TIME
# purpose : find current time
# arguments : none
# returns : string containing current time as hh::mm::ss
CURRENT_TIMESTAMP
# purpose : find current date and time
# arguments : none
# returns : string containing current timestamp as yyyy-mm-dd hh::mm::ss
String Functions
char_length, lower, position, regex, soundex, substring, trim, upper
CHAR_LENGTH
# purpose : find length in characters of a string
# arguments : a string
# returns : a number - the length of the string in characters
LOWER & UPPER
# purpose : lower-case or upper-case a string
# arguments : a string
# returns : the sting lower or upper cased
POSITION
# purpose : find first position of a substring in a string
# arguments : a substring and a string possibly containing the substring
# returns : a number - the index of the substring in the string
# or 0 if the substring doesn't occur in the sring
REGEX
# purpose : test if a string matches a perl regular expression
# arguments : a string and a regex to match the string against
# returns : boolean value of the regex match
#
# example : ... WHERE REGEX(col3,'/^fun/i') ... matches rows
# in which col3 starts with "fun", ignoring case
SOUNDEX
# purpose : test if two strings have matching soundex codes
# arguments : two strings
# returns : true if the strings share the same soundex code
#
# example : ... WHERE SOUNDEX(col3,'fun') ... matches rows
# in which col3 is a soundex match for "fun"
CONCAT
# purpose : concatenate 1 or more strings into a single string;
# an alternative to the '||' operator
# arguments : 1 or more strings
# returns : the concatenated string
#
# example : SELECT CONCAT(first_string, 'this string', ' that string')
# returns "<value-of-first-string>this string that string"
# note : if any argument evaluates to NULL, the returned value is NULL
COALESCE aka NVL
# purpose : return the first non-NULL value from a list
# arguments : 1 or more expressions
# returns : the first expression (reading left to right)
# which is not NULL; returns NULL if all are NULL
#
# example : SELECT COALESCE(NULL, some_null_column, 'not null')
# returns 'not null'
DECODE
# purpose : compare the first argument against
# succeding arguments at position 1 + 2N
# (N = 0 to (# of arguments - 2)/2), and if equal,
# return the value of the argument at 1 + 2N + 1; if no
# arguments are equal, the last argument value is returned
# arguments : 4 or more expressions, must be even # of arguments
# returns : the value of the argument at 1 + 2N + 1 if argument 1 + 2N
# is equal to argument1; else the last argument value
#
# example : SELECT DECODE(some_column,
# 'first value', 'first value matched'
# '2nd value', '2nd value matched'
# 'no value matched'
# )
REPLACE, SUBSTITUTE
# purpose : perform perl subsitution on input string
# arguments : a string and a substitute pattern string
# returns : the result of the substitute operation
#
# example : ... WHERE REPLACE(col3,'s/fun(\w+)nier/$1/ig') ... replaces
# all instances of /fun(\w+)nier/ in col3 with the string
# between 'fun' and 'nier'
SUBSTRING
SUBSTRING( string FROM start_pos [FOR length] )
Returns the substring starting at start_pos and extending for "length"
character or until the end of the string, if no "length" is supplied.
Examples:
SUBSTRING( 'foobar' FROM 4 ) # returns "bar"
SUBSTRING( 'foobar' FROM 4 FOR 2) # returns "ba"
Note: The SUBSTRING function is implemented in SQL::Parser and
SQL::Statement and, at the current time, can not be over-ridden.
TRIM
TRIM ( [ [LEADING|TRAILING|BOTH] ['trim_char'] FROM ] string )
Removes all occurrences of <trim_char> from the front, back, or both
sides of a string.
BOTH is the default if neither LEADING nor TRAILING is specified.
Space is the default if no trim_char is specified.
Examples:
TRIM( string )
trims leading and trailing spaces from string
TRIM( LEADING FROM str )
trims leading spaces from string
TRIM( 'x' FROM str )
trims leading and trailing x's from string
Note: The TRIM function is implemented in SQL::Parser and
SQL::Statement and, at the current time, can not be over-ridden.
Special Utility FunctionsIMPORT()
CREATE TABLE foo AS IMPORT(?) ,{},$external_executed_sth
CREATE TABLE foo AS IMPORT(?) ,{},$AoA
Submitting built-in functions
There are a few built-in functions in the SQL::Statement::Functions.
If you make a generally useful UDF, why not submit it to me and have it
(and your name) included with the built-in functions? Please follow
the format shown in the module including a description of the arguments
and return values for the function as well as an example. Send them to
me at jzucker AT cpan.org with a subject line containing "built-in
UDF".
Thanks in advance :-).
ACKNOWLEDGEMENTS
Dean Arnold supplied DECODE, COALESCE, REPLACE, many thanks!
AUTHOR & COPYRIGHT
Copyright (c) 2005 by Jeff Zucker: jzuckerATcpan.org Copyright (c)
2009,2010 by Jens Rehsack: rehsackATcpan.org
All rights reserved.
The module may be freely distributed under the same terms as Perl
itself using either the "GPL License" or the "Artistic License" as
specified in the Perl README file.
perl v5.14.1 2011-02-01 SQL::Statement::Functions(3)
