MySQL存储过程变量格式在SELECT语句中不起作用

Question

I am having trouble getting a variable to work right in a MySQL Stored Procedure. Here is a sample of the stored procedure:

BEGIN

DECLARE x_parent varchar(100);
DECLARE term_ids_current varchar(100);
DECLARE term_ids_list INT(100);
DECLARE x_counter INT(11);
DECLARE y_counter INT(11);
DECLARE z_counter INT(11);

SET @term_ids_current = 189;
SET @term_ids_list = @term_ids_current;
SET @y_counter = 0;
SET @z_counter = 0;

parent_child: LOOP
    # used for debugging #
    SET @z_counter = @z_counter + 1;

    # first i check to see if my criteria is met to continue the loop. #
    IF EXISTS (SELECT tt.term_id FROM `bitnami_wordpress`.`wp_2_term_taxonomy` tt WHERE tt.parent IN (@term_ids_current)) THEN

        # used for debugging #
        SET @y_counter = @y_counter + 1;

        BEGIN

            DECLARE x_finished INT(11) DEFAULT 0;

            DECLARE parent_child_cursor CURSOR FOR
            SELECT tt.term_id FROM `bitnami_wordpress`.`wp_2_term_taxonomy` tt WHERE tt.parent IN (@term_ids_current);

            # declare NOT FOUND handler
            DECLARE CONTINUE HANDLER 
            FOR NOT FOUND SET x_finished = 1;

            OPEN parent_child_cursor;

                SET @x_counter = 0;

                single_parent: LOOP

                    FETCH parent_child_cursor INTO x_parent;

                    IF x_finished = 1 THEN
                        LEAVE single_parent;
                    ELSEIF @x_counter = 0 THEN
                        SET @term_ids_current = x_parent;
                    ELSE
                        SET @term_ids_current = CONCAT (x_parent,",",@term_ids_current);
                    END IF;

                    SET @x_counter = @x_counter + 1;

                END LOOP single_parent;

                SET @term_ids_list = CONCAT (@term_ids_current,",",@term_ids_list);

            CLOSE parent_child_cursor;

        END;
    ELSE
        LEAVE parent_child;
    END IF;

END LOOP parent_child;

# used for debugging #
SELECT @z_counter, @y_counter, @term_ids_current, @term_ids_list;

END;

In the single_parent loop I am populating the @term_ids_current variable with the results from my query. That variable is then used in the query for the main loop to determine if the criteria is still met. If it is then my loop happens again. I have tested each step of the procedure as an individual query and the results are accurate. The problem exists in getting the main query in the parent_child loop to run properly the second time.

When I run the SP above against my existing data set, the @term_ids_current variable contains this data set:

218,200,199,198,197,196,195,194,193,192,191,190

What I expect to happen is this data set is now passed in the query for the parent_child loop so that query would now be:

(SELECT tt.term_id FROM `bitnami_wordpress`.`wp_2_term_taxonomy` tt WHERE tt.parent IN (218,200,199,198,197,196,195,194,193,192,191,190))

When I run that query manually against my DB, the "IF EXISTS" statement is true meaning my parent_child loop should run again. But the loop is stopping after the IF EXISTS statement and not running again. I have verified this with the z_counter and y_counter variable. Every time I run the SP @z_counter = 2 and @y_counter = 1. So I know the IF statement is moving to the ELSE clause and not running.

To test this further I updated the SP and manually set my @term_ids_current variable at the end of the parent_child loop to see what would happen. So at the end of my altered SP I have set @term_ids_current this way:

SET @term_ids_current = (190,191,192,193,194,195,196,197,198,199,200,218);

    IF @z_counter = 2 THEN
        LEAVE parent_child;
    END IF;

I added the second IF statement to keep the SP from running an endless loop.

Now when I execute the SP I get this error message: "MySQL said: #1241 - Operand should contain 1 column(s)." So I updated the SP again to SET the @term_ids_current variable, but this time I used double quotes instead of parentheses.

SET @term_ids_current = "190,191,192,193,194,195,196,197,198,199,200,218";

With the variable manually set the SP returns the expected result. I have tried to use both CAST and CONVERT in my SELECT statement to have the variable treated as a string. Here is an example:

SELECT tt.term_id FROM `bitnami_wordpress`.`wp_2_term_taxonomy` tt WHERE tt.parent IN (CONVERT(@term_ids_current,CHAR));

This does not work. If I were doing this in Python I would transform the variable for the SELECT statement with:

str(@term_ids_current)

But I cannot find a way to do this same thing in MySQL.

So my question is, how can I get my variable @term_ids_current to be treated as a string to work properly in my SELECT statement?

Answer 1

The query

SELECT tt.term_id 
FROM `bitnami_wordpress`.`wp_2_term_taxonomy` tt 
WHERE tt.parent IN (@term_ids_current)

will not work if the @term_ids_current is a comma separated string. The reason for this is that @term_ids_current is treated as string and not as a set.

Couple of suggestions:

1. Instead of using a user defined variable (@var) use a temporary table for the current id's
2. It is better to use local variables (declare v_var int) instead of user defined variables in procedures as the scope of the user defined variable is the connection whereas the scope of the local variables is the procedure. This matters if your procedure calls other procedures that use same variables.

Answer 2

Try the suggestion given by @slaakso or use find_in_set

so you need to change the in clause into something similar to your codes

WHERE find_in_set(tt.parent,@term_ids_current)