如何在php中编写mysql用户自定义函数

Please tell me how to define MySQL User Defined Function with in PHP...

I'm using following code.but it is not working.

it throws error :

" (1313) RETURN is only allowed in a FUNCTION "

$mysqli = new mysqli( $DBHost, $DBUserName, $DBPassword, $DBName );


$Query =
"CREATE PROCEDURE FunGetRegistryValue(OUT Param_RegistryKey varchar(40))
BEGIN
    DECLARE vResult varchar(90);
    SELECT  iFnull(Value,'') INTO vResult FROM Project_Registry Where RegistryKey=Param_RegistryKey;
    RETURN(vResult);
END;";

if( !$mysqli->query( $Query ) ) {
    echo "Stored procedure creation failed: (" . $mysqli->errno . ") " . $mysqli->error;
}

When i use FUNCTION keyword instead of PROCEDURE then i get syntax error...

Please give me example code for "VALUE RETURNING FUNCTION"

$mysqli = new mysqli( $DBHost, $DBUserName, $DBPassword, $DBName );

$Query =
"DROP FUNCTION IF EXISTS FunGetRegistryValue;

CREATE   FUNCTION FunGetRegistryValue(Param_RegistryKey VARCHAR(40)) RETURNS VARCHAR(90) CHARSET latin1
   DETERMINISTIC
BEGIN
   DECLARE vResult VARCHAR(90);
   SELECT  IFNULL(VALUE,'') INTO vResult FROM Project_Registry WHERE RegistryKey=Param_RegistryKey;
   RETURN(vResult);
   END;";

if( !$mysqli->multi_query( $Query ) ) {
    echo $mysqli->error;
    exit();
}

DELIMITER $$ 
CREATE DEFINER=root@localhost
FUNCTION FunGetRegistryValue(Param_RegistryKey varchar(40)) 
RETURNS varchar(90) 
CHARSET latin1 DETERMINISTIC 
BEGIN 
    DECLARE vResult varchar(90); 
    SELECT iFnull(Value,'') INTO vResult 
    FROM Project_Registry Where RegistryKey=Param_RegistryKey;
    RETURN(vResult); 
END$$ 
DELIMITER ;

originally a comment by Fozia. I added it as an answer so that it's not a jumbled run on query and is legible.