MySQL - 저장 프로시저(Stored Procedure), 커서(Cursor) 사용 예제

CREATE PROCEDURE curdemo()
BEGIN
  DECLARE done INT DEFAULT 0;
  DECLARE a CHAR(16);
  DECLARE b,c INT;
  DECLARE cur1 CURSOR FOR SELECT id,data FROM test.t1;
  DECLARE cur2 CURSOR FOR SELECT i FROM test.t2;
  DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;

  OPEN cur1;
  OPEN cur2;

  read_loop: LOOP
    FETCH cur1 INTO a, b;
    FETCH cur2 INTO c;
    IF done THEN
      LEAVE read_loop;
    END IF;
    IF b < c THEN
      INSERT INTO test.t3 VALUES (a,b);
    ELSE
      INSERT INTO test.t3 VALUES (a,c);
    END IF;
  END LOOP;

  CLOSE cur1;
  CLOSE cur2;
END;

 출처 : MySQL 5.0 Reference Manual

심플하면서도... 안 쓰다 쓸 때 한 번에 기억을 재생시켜주기에는 충분한 예제

CREATE DEFINER=`root`@`localhost` PROCEDURE `foo`.`usp_cursor_example`(
  IN name_in VARCHAR(255)
)
READS SQL DATA
BEGIN

  /*
    All 'DECLARE' statements must come first
  */

  -- Declare '_val' variables to read in each record from the cursor
  DECLARE name_val VARCHAR(255);
  DECLARE status_update_val VARCHAR(255);

  -- Declare variables used just for cursor and loop control
  DECLARE no_more_rows BOOLEAN;
  DECLARE loop_cntr INT DEFAULT 0;
  DECLARE num_rows INT DEFAULT 0;

  -- Declare the cursor
  DECLARE friends_cur CURSOR FOR
    SELECT
        name
      , status_update
    FROM foo.friend_status
    WHERE name = name_in;

  -- Declare 'handlers' for exceptions
  DECLARE CONTINUE HANDLER FOR NOT FOUND
    SET no_more_rows = TRUE;

  /*
    Now the programming logic
  */

  -- 'open' the cursor and capture the number of rows returned
  -- (the 'select' gets invoked when the cursor is 'opened')
  OPEN friends_cur;
  select FOUND_ROWS() into num_rows;

  the_loop: LOOP

    FETCH  friends_cur
    INTO   name_val
    ,      status_update_val;

    -- break out of the loop if
      -- 1) there were no records, or
      -- 2) we've processed them all
    IF no_more_rows THEN
        CLOSE friends_cur;
        LEAVE the_loop;
    END IF;

    -- the equivalent of a 'print statement' in a stored procedure
    -- it simply displays output for each loop
    select name_val, status_update_val;

    -- count the number of times looped
    SET loop_cntr = loop_cntr + 1;

  END LOOP the_loop;

  -- 'print' the output so we can see they are the same
  select num_rows, loop_cntr;

END
DELIMITER ;
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