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Improve PHP Performance by Caching Database Results

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LEARN ABOUT PHP

sqlite_create_function

SQLITE_CREATE_FUNCTION(3)												 SQLITE_CREATE_FUNCTION(3)

sqlite_create_function - Registers a ";regular" User Defined Function for use in SQL statements

SYNOPSIS

       void sqlite_create_function (resource  $dbhandle, string  $function_name, callable  $callback, [int  $num_args = -1])

DESCRIPTION

       Object oriented style (method): void SQLiteDatabase::createFunction (string  $function_name, callable  $callback, [int  $num_args = -1])

       sqlite_create_function(3)  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.

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

PARAMETERS

	      o $dbhandle
		- The SQLite Database resource; returned from sqlite_open(3) when used procedurally. This parameter is not required when using the
		object-oriented method.

	      o $function_name
		- The name of the function used in SQL statements.

	      o $callback
		- Callback function to handle the defined SQL function.

	      Note

		      Callback functions should return a type understood by SQLite (i.e. scalar type).

	      o $num_args
		- Hint to the SQLite parser if the callback function accepts a predetermined number of arguments.

       Note

	      Two  alternative	syntaxes are supported for compatibility with other database extensions (such as MySQL). The preferred form is the
	      first, where the $dbhandle parameter is the first parameter to the function.

RETURN VALUES

	No value is returned.

EXAMPLES

       Example #1

	      sqlite_create_function(3) 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 with-
       out 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(3) 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(3) and sqlite_udf_decode_binary(3) 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(3) and sqlite_create_aggregate(3) to override SQLite native SQL functions.

SEE ALSO

       sqlite_create_aggregate(3).

PHP Documentation Group 												 SQLITE_CREATE_FUNCTION(3)