Can MySQL Execute a String as a Query Like JavaScript\'s eval()?

Can MySQL Execute a String as a Query?

Question:

In a MySQL environment, attempting to execute a stored procedure that passes in a varchar as a query via EXEC or CALL has proven unsuccessful. Is there a MySQL equivalent to JavaScript's eval function that would make this possible?

Answer:

Yes, the following technique provides a MySQL implementation similar to JavaScript's eval:

1. Define an SQL variable (@queryString) using CONCAT to dynamically generate the query string from the varchar parameter.
2. Prepare a statement (stmt) based on @queryString using PREPARE.
3. Execute the prepared statement (stmt) using EXECUTE.
4. Deallocate the prepared statement using DEALLOCATE PREPARE.
5. Reset the SQL variable (@asd) to NULL.

For instance:

SET @queryString = (
SELECT CONCAT('INSERT INTO user_group (`group_id`,`user_id`) VALUES ', www.vals) as res FROM (
    SELECT GROUP_CONCAT(qwe.asd SEPARATOR ',') as vals FROM ( 
           SELECT CONCAT('(59,', user_id, ')') as asd FROM access WHERE residency = 9 
    ) as qwe 
) as www
);

PREPARE stmt FROM @queryString;
EXECUTE stmt;
DEALLOCATE PREPARE stmt; 
SET @asd = NULL;

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