Problems while creating a MySQL function

Question

I have a PHP function to create those famouse AlphaID representations of integers as follows:

function alphaID( $input ) {

    $index = 'abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ';

    $base    = strlen( $index );
    $input  += pow( $base, 4 );
    $output  = '';

    for( $i = floor( log( $input, $base ) ); $i >= 0; $i-- ) {

        $bcp     = bcpow( $base, $i );
        $start   = floor( $input / $bcp ) % $base;
        $output .= substr( $index, $start, 1 );
        $input   = $input - ( $start * $bcp );
    }

    return $output;
}

Encoding, for example, the maximum integer provided by PHP_MAX_INT constant (2147483647) would return cwuCBb

But I thought it was a little too slow in the whole application picture so I tried to create a MYSQL function so, theoretically, I wouldn't waste performance doing such conversion with PHP once data would come ready for me while querying.

The MySQL manual is not exactly friendly, but searching here and there I came up to this:

DROP FUNCTION IF EXISTS ENCODE_ALPHAID;

DELIMITER $$

CREATE FUNCTION ENCODE_ALPHAID( input integer ) RETURNS CHAR( 6 ) DETERMINISTIC

BEGIN

    DECLARE output CHAR( 6 );

    DECLARE letters CHAR( 62 );
    DECLARE base TINYINT( 2 );

    DECLARE iterator TINYINT( 2 );
    DECLARE bcp CHAR( 9 );
    DECLARE start TINYINT( 2 );

    SET output   = '';

    SET letters  = 'abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ';

    SET base     = CHAR_LENGTH( letters );
    SET input    = input + POW( base, 4 );

    SET iterator = FLOOR( LOG( base, input ) );

    ENCODING: LOOP

        SET bcp      = POW( base, iterator );
        SET start    = FLOOR( input / bcp ) % base + 1;

        SET output   = CONCAT( output, SUBSTR( letters, start, 1 ) );

        SET input    = input - ( start * bcp );

        SET iterator = iterator-1;

        IF iterator < 0 THEN LEAVE ENCODING; END IF;

    END LOOP ENCODING;

    RETURN output;

END $$

DELIMITER ;

But when I ran it through the MySQL manager I use (DBNinja), apparently, nothing happens. After run the query it shows 0 row affected and I'm not sure if this is the expected output or not.

Right or not, the function didn't work either way because when I tried to use it in a query:

SELECT ENCODE_ALPHAID( `c`.`cid` ) from `table` c WHERE `c.user` = 1

I first received an error saying table.ENCODE_ALPHAID didn't exist. Then I noticed that, indeed, I created the function while in a different database of the one I was trying to use.

But I created it again, in the proper database, but the same error came up.

So here are the questions:

1. What did I do wrong? This is the very first time I try to do something like that and I'm not exactly sure
2. My implementation of the PHP code is a valid MySQL counterpart? Did I miss anything?
3. Can I make this function "global"? I mean, available to any database I need it? Because for the application I'm working on, in order to keep the two subsystems involved separated, I created two databases.

Updated

Apparently the problem with the function not being created is on DBNinja's end, because I ran the statement directly in MySQL console and, although with the same output status of 0 rows affected, I was able to effectively use the function in a statement, so the function was created afterall.

However, something is wrong with the routine itself because when I tested it, the resulting string was... "one ahead".

For example, if I run the following PHP code:

echo alphaID( 2 );

It would produce baaac, but the MySQL function is returning baaad, which would be the AlphaID representation of the integer 3

Not only this is wrong, but I think it could also overflow the INT type used when reaching the maximum 2147483647

Answer 1

Bruno, from MySQL version you are missing:

1. $input += pow( $base, 4 );
2. SUBSTR in PHP starts from 0, in MySQL it starts from 1.

3. The loop ending condition should be:

   IF iterator < 0 THEN LEAVE ENCODING; END IF;

4. When using CONCAT, make sure you do not CONCAT NULL's (you should initialize parameters)

Routines are always created in one database. You can call them in any of them (if you have privileges) by including the database name in the query:

call mydb.ENCODE_ALPHAID( 2147483647 );

Also, when declaring variables, you might want to use prefixes so that the variables do not get mixed up with possible column names / reserved words. For example instead of "output" use "v_output".

Answer 2

Seems like you were missing END IF; Do not use reserved words for variables. If you want to go the evil way make sure you quote them .ie ` table``, . Note the back tick - not single quotes. On my machine this code returns null:

CREATE DEFINER=`root`@`localhost` FUNCTION `ENCODE_ALPHAID`(`input` INT)
RETURNS CHAR(6) DETERMINISTIC NO SQL SQL SECURITY DEFINER 
BEGIN     
DECLARE output CHAR(6);
DECLARE `index` CHAR(62); 
DECLARE base TINYINT(2); 
DECLARE iterator TINYINT( 2 );
DECLARE bcp CHAR( 9 ); 
DECLARE start TINYINT( 2 ); SET `index` = 'abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ'; 
SET base = CHAR_LENGTH( `index` ); 
SET iterator = FLOOR( LOG( base, input ) ); 
ENCODING: LOOP
SET bcp = POW( base, iterator ); 
SET start = FLOOR( input / bcp ) % base;
SET output = CONCAT( output, SUBSTR( `index`, start, 1 ) ); 
SET input = input - ( start * bcp );
SET iterator = iterator-1;
IF iterator >= 0 THEN LEAVE ENCODING; 
END IF;
   END LOOP ENCODING; 
   RETURN output; 
END;

PS: On the back tick use one. I have no idea how to escape markdown. And eaid is the shorter name I was using