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                            sqlite_create_function

   (no version information, might be only in CVS)
   sqlite_create_function --  Registers a "regular" User Defined Function
   for use in SQL statements.

Description

   bool sqlite_create_function ( resource dbhandle, string function_name,
   mixed callback [, int num_args])

   sqlite_create_function() allows you to register a PHP function with
   SQLite as an UDF (User Defined Function), so that it can be called
   from within your SQL statements.

   dbhandle specifies the database handle that you wish to extend,
   function_name specifies the name of the function that you will use in
   your SQL statements, callback is any valid PHP callback to specify a
   PHP function that should be called to handle the SQL function. The
   optional parameter num_args is used as a hint by the SQLite expression
   parser/evaluator. It is recommended that you specify a value if your
   function will only ever accept a fixed number of parameters.

   The UDF can be used in any SQL statement that can call functions, such
   as SELECT and UPDATE statements and also in triggers.

   Example 1. sqlite_create_function() example
   <?php
   function md5_and_reverse($string) {
       return strrev(md5($string));
   }
   if ($dbhandle = sqlite_open('mysqlitedb', 0666, $sqliteerror)) {

       sqlite_create_function($dbhandle, 'md5rev', 'md5_and_reverse', 1);

       $sql  = 'SELECT md5rev(filename) FROM files';
       $rows = sqlite_array_query($dbhandle, $sql);
   } else {
       echo 'Error opening sqlite db: ' . $sqliteerror;
       exit;
   }
   ?>

   In this example, we have a function that calculates the md5 sum of a
   string, and then reverses it. When the SQL statement executes, it
   returns the value of the filename transformed by our function. The
   data returned in $rows contains the processed result.

   The beauty of this technique is that you do not need to process the
   result using a foreach() loop after you have queried for the data.

   PHP registers a special function named php when the database is first
   opened. The php function can be used to call any PHP function without
   having to register it first.

   Example 2. Example of using the PHP function
   <?php
   $rows = sqlite_array_query($dbhandle, "SELECT php('md5', filename)
   from files");
   ?>

   This example will call the md5() on each filename column in the
   database and return the result into $rows

     Note: For performance reasons, PHP will not automatically
     encode/decode binary data passed to and from your UDF's. You need
     to manually encode/decode the parameters and return values if you
     need to process binary data in this way. Take a look at
     sqlite_udf_encode_binary() and sqlite_udf_decode_binary() for more
     details.

     Tip: It is not recommended to use UDF's to handle processing of
     binary data, unless high performance is not a key requirement of
     your application.

     Tip: You can use sqlite_create_function() and
     sqlite_create_aggregate() to override SQLite native SQL functions.

   See also sqlite_create_aggregate().
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