Can MySQL triggers be created with dynamic SQL from within a stored procedure?

问题

Is it possible to create a trigger in MySQL using dynamically generated SQL from within a stored procedure? I am executing other dynamically constructed queries in my procedure by preparing a statement, but when I try the same approach to create a trigger I get the following error:

ERROR Code: 1295This command is not supported in the prepared statement protocol yet

From Bug #31625, PREPARED STATEMENT syntax does not allow to create TRIGGERS I see other people have been complaining about the same thing since 2007.

And from the look of WL#2871: Prepare any SQL it has not yet been fixed.

Is there a workaround for this problem? Is there another way of creating triggers with dynamic SQL?

Basically what I am trying to do is dynamically create triggers for recording audit data for inserts on various different tables. I am listing the tables I want to audit in an *audit_tables* table. The stripped-down procedure below iterates over the entries in that table and tries to create the trigger.

drop procedure if exists curtest;
delimiter |
create procedure curtest()
BEGIN
    DECLARE done INT DEFAULT 0;
    declare tn varchar(16);
    declare cur cursor for select table_name from audit_tables;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;
    OPEN cur;
    read_loop: LOOP
        fetch cur into tn;
        if done then
            leave read_loop;
        end if;

        /* Create the BEFORE INSERT trigger */
        set @sql = concat('CREATE TRIGGER audit_', tn, '_bi BEFORE INSERT ON ', tn, '
            FOR EACH ROW BEGIN
                set new.foo="bar";
            END;');
        PREPARE stmt FROM @sql;
        EXECUTE stmt;
        DEALLOCATE  PREPARE stmt;
    end LOOP;
    close cur;
END;
|
delimiter ;

call curtest();

回答1:

As the error you mention says, the CREATE TRIGGER command is not supported within prepared statements.

I think a more viable option is to use a scripting language that has MySQL bindings, like PHP, to automate the trigger creation. By the way, I just remembered that MySQL Workbench uses Lua as a scripting language for this sort of things.

来源：https://stackoverflow.com/questions/5981396/can-mysql-triggers-be-created-with-dynamic-sql-from-within-a-stored-procedure

标签

mysql

triggers

dynamic-sql