MySQL/ MariaDB Error Code: 1329. No data – zero rows fetched, selected, or processed

The above error can occur when calling a cursor results in no rows, or no more rows if called in a loop. Whilst the error message is descriptive about what has happened physically, you may wish to catch the error so that you can do something else, or simply replace the generic database error with something more meaningful. 

If you’re not sure what I’m talking about, run the following code on a MySQL or MariaDB database:

DROP PROCEDURE IF EXISTS test_error;

DELIMITER $$
CREATE PROCEDURE test_error() 
BEGIN 
    DECLARE temp_column_name VARCHAR(100);
        
	DECLARE c_example CURSOR FOR 
        SELECT   column_name
        FROM     information_schema.columns
        WHERE    column_name != column_name;
    -- Get data from example cursor
    OPEN c_example;
    FETCH c_example INTO temp_column_name;
    CLOSE c_example;
  
END$$
DELIMITER ;

CALL test_error();

The response is:

Error Code: 1329. No data - zero rows fetched, selected, or processed

In order to trap the error we need to define a CONTINUE HANDLER and DECLARE a variable for the CONTINUE HANDLER to set. We can then manage the No data exception simply by checking the variable.

Following on from the above example, we’ve introduced a variable ch_done. When this variable is set to 1 then the last cursor to be FETCHed returned No data. If it returns a zero then data was returned and all is well.

DROP PROCEDURE IF EXISTS test_error;

DELIMITER $$
CREATE PROCEDURE test_error() 
BEGIN 
    DECLARE ch_done INT DEFAULT 0;
    DECLARE temp_column_name VARCHAR(100);
        
	DECLARE c_example CURSOR FOR 
        SELECT   column_name
        FROM     information_schema.columns
        WHERE    column_name != column_name;

    DECLARE CONTINUE HANDLER FOR NOT FOUND SET ch_done = 1;
    
    -- Get data from example cursor
    OPEN c_example;
    FETCH c_example INTO temp_column_name;
    CLOSE c_example;
    
    IF(ch_done = 1) THEN 
        -- handle the No data error!
        SELECT 'Oh no!';
    END IF;
  
END$$
DELIMITER ;

CALL test_error();

Remember, if you call multiple cursors in a row, you may need to reset the ch_done back to 0.

How to exit from a MySQL/ MariaDB Stored Procedure/ Function Prematurely

MySQL and MariaDB enable you to define your own error conditions and to report back to the SQL client both a return code and an error message. As soon as you raise the condition then MySQL/ MariaDB will halt any further execution of the code and report the error back to the client. This can help the user calling the function understand what went wrong, rather than seeing a generic database error message.

DECLARE error_flag INT DEFAULT 0;
DECLARE REF_MISSING CONDITION FOR SQLSTATE '45000';

-- Your code, set the error_flag in the event of an error

IF (error_flag) THEN
    SIGNAL REF_MISSING
    SET MESSAGE_TEXT = 'An error occurred!';
END IF;

The above code defines a custom condition with an error code of 45000 which is the suggested user defined error code. Other error codes are available, which you may have seen, but are reserved by the database server to use for specific database error events – it’s best not to mix your user defined messages with these. The function then checks if the error_flag has been set and, if it has, halts further code execution and returns the error “An error occurred!” to the client.

You could simplify this by just calling the below code at the point the error is detected, if you are already catching an error event in your stored procedure or function by simply using the below code without the error_flag declaration.

SIGNAL REF_MISSING
SET MESSAGE_TEXT = 'An error occurred!';