MYSQL cursor loop, runs one extra round, why?

问题

I'm looping through a cursor result set in a MYSQL stored procedure. I'm facing an issue which is that the loop always run thorough the last record twice. Here is my code,

BEGIN
DECLARE not_found_creadit INT DEFAULT 0;

DECLARE cur_credit CURSOR FOR 
SELECT customer_id, amount, status, user_type, employee, note FROM credit WHERE status = 'approved' AND customer_id = int_cust_id;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET not_found_creadit = 1;
OPEN cur_credit;
  SET not_found_creadit = 0;
  credit_loop : LOOP 
      IF not_found_creadit THEN
        CLOSE cur_credit;
        LEAVE credit_loop;
      END IF;
      FETCH cur_credit INTO vc_customer, dec_amount, vc_status, vc_user_type, vc_emp, vc_note;
      SELECT vc_customer, dec_amount, vc_status, vc_user_type, vc_emp, vc_note;
      ......
      ......
  END LOOP;
END;

Means if I have 3 records, loop runs 4 times, if it is 10 records loop runs 11 times, etc. Any idea whats happening here?

回答1:

The handler, which sets not_found_creadit = 1, is fired when the FETCH returns no rows, but you are checking its value before executing FETCH, so the main body of your loop will execute one extra time when the FETCH fails, then the loop loop exits at the start of the next iteration.

Rearrange your code to check the value of your variable immediately after the FETCH:

credit_loop : LOOP 
    FETCH cur_credit INTO vc_customer, dec_amount, vc_status, vc_user_type, vc_emp, vc_note;
    IF not_found_creadit THEN
        CLOSE cur_credit;
        LEAVE credit_loop;
    END IF;
    SELECT vc_customer, dec_amount, vc_status, vc_user_type, vc_emp, vc_note;
    ......
    ......
END LOOP;

Also, consider correcting the spelling of your variable to not_found_credit

回答2:

YOU MUST CORRECT TYPE BECAUSE I WRITE DEFAULT (i dont know what You have in table credit). End If U create table TempTable use

TRUNCATE TempTable;

Please rewrite example

CREATE CREATE TEMPORARY TABLE TempTable (`Id` int(11) NOT NULL auto_increment,
  `customer_id` int(11) NOT NULL,
  `amount` int(11) NOT NULL,
  `status` varchar(1000) NOT NULL,
  `user_type` int(11) NOT NULL default '0',
  `employee` varchar(1000) NOT NULL,
  PRIMARY KEY  (`customer_id`),
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_polish_ci AUTO_INCREMENT=1 ;");

ofcourse type is bad :)

 DELIMITER $$
    DROP PROCEDURE IF EXISTS CursorX $$
    CREATE PROCEDURE `CursorX`()
    BEGIN    
            DECLARE xCustomerId int(11);  
            DECLARE xStatus   int(11);
            DECLARE xUserType  varchar(255);
            DECLARE xEmployee  varchar(255);
            DECLARE xNote varchar(255);  
            DECLARE i int(11);
            DECLARE recordNotFound INTEGER DEFAULT 0;
            DECLARE cur_credit CURSOR FOR SELECT customer_id, amount, status, user_type, employee, note FROM credit WHERE status = 'approved' AND customer_id = int_cust_id;
            DECLARE CONTINUE HANDLER FOR NOT FOUND SET recordNotFound = 1;

            DROP TEMPORARY TABLE IF EXISTS TempTable;
            CREATE TEMPORARY TABLE TempTable AS(SELECT * FROM credit);

            OPEN cur_credit;
            set not_found_creadit = 0;
            credit_loop: LOOP
            SET i = i +1;
                FETCH cur_credit INTO xCustomerId,xStatus,xUserType,xEmployee,xNote;
                IF not_found_creadit THEN
                    LEAVE credit_loop;
                 END IF;
            END LOOP credit_loop;
            CLOSE cur_credit;
    select * FROM TempTable;

    END $$

来源：https://stackoverflow.com/questions/12291573/mysql-cursor-loop-runs-one-extra-round-why

标签

mysql

loops

stored-procedures

cursor