MySQL Error 1337 – SQLSTATE: 42000 (ER_SP_CURSOR_AFTER_HANDLER) is an error that arises when the declaration of a cursor occurs after the declaration of a handler within a stored procedure or function. The error message “Cursor declaration after handler declaration” indicates that MySQL expects cursors to be declared before any handlers in the body of a stored routine.
Understanding the Error
In MySQL, the order in which cursors and handlers are declared in stored procedures or functions is significant. Handlers are used to specify actions to be taken in response to certain conditions, such as warnings or errors, while cursors are used to iterate through result sets returned by SELECT queries. MySQL enforces the rule that all cursor declarations must precede handler declarations.
Diagnosing the Problem
To fix this error, review the structure of your stored routine:
- Check the Order of Declarations: Identify where cursors and handlers are declared and ensure that cursors come first.
- Understand the Logical Flow: Recognize that cursor declarations must be placed at the beginning of the routine, before any condition handling logic is defined.
Fixing the Error
Here are examples of how to correct Error 1337 by adjusting the order of declarations:
- Correct Order with Single Cursor and Handler:
CREATE PROCEDURE process_data() BEGIN DECLARE done INT DEFAULT FALSE; DECLARE my_cursor CURSOR FOR SELECT column FROM my_table; DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;-- Cursor operationsEND;In this example, the cursor is declared before the handler, which is the correct sequence.
- Correct Order with Multiple Cursors and Handlers:
CREATE PROCEDURE complex_processing() BEGIN DECLARE no_more_rows BOOLEAN; DECLARE cursor1 CURSOR FOR SELECT column1 FROM table1; DECLARE cursor2 CURSOR FOR SELECT column2 FROM table2;DECLARE CONTINUE HANDLER FOR NOT FOUND SET no_more_rows = TRUE; -- Cursor operationsEND;Here, both cursors are declared before any handler, adhering to MySQL’s requirements.
- Avoiding Common Mistakes:
CREATE PROCEDURE example_procedure() BEGIN DECLARE not_found BOOLEAN; DECLARE cursor_example CURSOR FOR SELECT id FROM example_table;DECLARE CONTINUE HANDLER FOR SQLSTATE '02000' SET not_found = TRUE; -- Cursor operationsEND;Again, the cursor is declared before the handler, which is the correct order.
- Always start with cursor declarations immediately after the BEGIN statement of your stored routine.
- Follow cursor declarations with handler declarations before proceeding to the main logic of your routine.
- Review the MySQL documentation on stored procedures and functions to familiarize yourself with best practices and the expected structure of routines.
- Test your stored procedures after restructuring to ensure that they function correctly with the new declaration order.
By ensuring that cursors are declared before handlers in your stored procedures and functions, you can resolve MySQL Error 1337 and create routines that execute smoothly without declaration order issues.