Question

I am writing a stored procedure, which opens a cursor to a table, and then iterate through all records. In the iterating process I create a dynamic query based on the results of the first cursor.

I need to open the cursor on dynamic SQL, but MySQL is not allowing me to do so. According to the official doc of MySQL: "Cursors must be declared before declaring handlers. Variables and conditions must be declared before declaring either cursors or handlers".

Here is the script:

DELIMITER $$

DROP PROCEDURE IF EXISTS sp_test$$

CREATE PROCEDURE `sp_test`()
BEGIN
    -- Declarations
    
    DECLARE prepared_sql VARCHAR(1000);
    DECLARE index_count INT;

    -- Cursors
    DECLARE cursor1 CURSOR FOR SELECT * from table1;
    -- Continue Handler for Cursor
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET no_more_rows = TRUE;
    -- Open cursors
    OPEN cursor1;

    -- Business Logic
    all_alerts_loop: LOOP
        -- Fetch record from cursor1 and create a dynamic sql
                
        -- Check if cursor has reached to end than leave the loop
        IF no_more_rows THEN
            LEAVE all_alerts_loop;
        END IF;
        
        
        WHILE @some_other_variable <> 0
        DO
                              -- I want to open cursor 2 on this sql
            -- set @prepared_sql =  'create dynamic sql here';  
                    END WHILE;
        
                    -- This works fine
        PREPARE stmt FROM @prepared_sql;
        EXECUTE stmt;

                    -- But can't define cursor here? so what is the solution
                    -- Gives syntax error, I have tried with @prepared_sql also rather than stmt
        DECLARE cursor2 CURSOR FOR stmt;
        
    END LOOP;
    
    -- closing cursors
    CLOSE cursor1;
    END$$

DELIMITER ;

Any idea on how to create cursor for a dynamic query? in MySQL?

Answer 1

Create an another Procedure and write the code of cursor in this new procedure and then call the procedure from where u want to declare a cursor…