Procedure to USE dynamic database name on Multi Table Delete

Question

I'm trying to make a procedure for MySQL 5.1 that will take a database name as an argument and issue a MULTI DELETE inside that database. I'm running into two problems that I'm not sure how to work around:

• USE can't be used in a prepared statement. When I try, I get "This command is not supported in the prepared statement protocol yet".
• MULTI DELETEs can't delete a table in a different database. When I try, I get "Unknown table 'x' in MULTI DELETE".

A code sample is as follows:

DELIMITER $$
CREATE PROCEDURE multi_test (
    IN dbname VARCHAR(20)
)
BEGIN
    SET @us = CONCAT('USE ', dbname, ';');
    PREPARE ustmt FROM @us;
    EXECUTE ustmt;
    DEALLOCATE PREPARE ustmt;
    SET @s = CONCAT('DELETE t FROM ', dbname, '.t as t INNER JOIN ', dbname, '.t2 as t2 IN t.f_id = t2.id');
    PREPARE stmt FROM @s;
    EXECUTE stmt;
    DEALLOCATE PREPARE stmt;
END $$
DELIMITER ;

Again, this results in "This command is not supported in the prepared statement protocol yet".

One other objective is to keep this in MySQL - I'd rather not use a scripting language that connects to MySQL, but rather just have some MySQL procedure that I can call from a client CLI. However, I'm not opposed to having procedures in other languages (like you can do in PostgreSQL) if that's possible in MySQL.

Answer 1

It appears I need to use the dbname and the table ALIAS when trying to use a MULTI DELETE.

DELETE dbname.talias FROM dbname.t as talias INNER JOIN dbname.t2 as t2 ON talias.f_id = t2.id

I believe I had tried that and it failed, but it now appears to be working :-/