执行存储在列中的 SQL 查询时出现 MYSQL 错误

Question

I have two tables,

execution:

execution_id | order_id | execution_date
   1             1             2014-03-16
   2             1             2014-03-17

and queries:

query_name | code
  CNT_EXEC |  SELECT COUNT(execution_id) FROM `execution` 

We have query defined in a column above. I am trying to execute this query using my code below;

DELIMITER //

DROP PROCEDURE IF EXISTS query_execute //
CREATE PROCEDURE query_execute()

BEGIN
    DECLARE finished INTEGER DEFAULT 0;
    DECLARE s_query varchar(255);

    DECLARE c_queries CURSOR FOR 
    SELECT code FROM queries;/*since there are more than one queries in the actual query table*/
    
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET finished = 1;
    
    OPEN c_queries;

    getquery: LOOP
        FETCH c_queries INTO s_query;
    
        IF finished = 1 THEN 
           LEAVE getquery;
        END IF;
    
        /*run the query*/
        SET @sql = s_query;
        PREPARE stmt FROM  @sql;
        EXECUTE stmt;
        DEALLOCATE PREPARE stmt;
    
    END LOOP;
    
END //

DELIMITER ;

 /*next I am trying to invoke the procedure and find the results*/

CREATE PROCEDURE queriesExecution()
BEGIN

SELECT query_name, query_execute() AS val
  FROM queries;

END

Going by the MySQL documentation, it seems I am using the correct procedure to create the procedure.But here is the error I am getting;

ERROR 1064 (42000) in the pre-written template: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 5`.

Answer 1

As i already wrote in my comment, your approach doesn't work .

But you can change it a bit

First:

Change your queries, because you need a result

CREATE TABLE queries (
  `query_name` VARCHAR(8),
  `code` VARCHAR(355)
);

INSERT INTO queries
  (`query_name`, `code`)
VALUES
  ('CNT_EXEC', 'SELECT COUNT(execution_id) INTO @result  FROM `execution`');

As you can see the result is put into a user defined variable. so that ot can be used in the INSERT INT myresult

DELIMITER //

DROP PROCEDURE IF EXISTS query_execute //
CREATE PROCEDURE query_execute()

BEGIN
    DECLARE finished INTEGER DEFAULT 0;
    DECLARE s_query varchar(255);

    DECLARE c_queries CURSOR FOR 
    SELECT code FROM queries;/*since there are more than one queries in the actual query table*/
    
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET finished = 1;
    CREATE TEMPORARY TABLe myresults(`query` varchar(255), result INT);
    OPEN c_queries;

    getquery: LOOP
        FETCH c_queries INTO s_query;
    
        IF finished = 1 THEN 
           LEAVE getquery;
        END IF;
    
        /*run the query*/
        SET @sql = s_query;
        PREPARE stmt FROM  @sql;
        EXECUTE stmt;
        INSERT INTO myresults VALUES (s_query,@result);
        DEALLOCATE PREPARE stmt;
    
    END LOOP;
    SELECT * FROM myresults;
    DROP TEMPORARY TABLE myresults;
END //

DELIMITER ;

when you now call CALL query_execute();

you get

query                                                        result
SELECT COUNT(execution_id) INTO @result  FROM `execution`    2

Of course as you add queries, you will get more rows.

this now assumes you get only INTEGER back in your queries, if not you must change the datatype.

This also only works, because your query returns only 1 result, if get more rows you can't use the user defined variables and you have to look for another approach.