在MySQL中使用游标时,从DECLARE语句调用存储过程

Question

我试图在MySQL中使用游标多次调用存储过程.我想多次将其称为my_id某个临时表中存在的值,并迭代这些ID并连接结果.

无论如何,我在这部分过程中遇到了麻烦:

  DECLARE curs CURSOR FOR  
    SELECT something FROM somewhere;

我不想从某个地方选择一些东西.我想要类似的东西

  DECLARE curs CURSOR FOR  
    CALL storedproc(@an_id);

该DECLARE语句可以用于调用存储过程吗？或者它必须与SELECT唯一相关联？谷歌搜索,我担心后者是这样的.

Answer 1

使用游标需要一些标准的样板代码来包围它.

使用游标从表中为每组值调用存储过程需要基本相同的样板.您SELECT想要传递的值,从您获取它们的位置(可以是临时表,基表或视图,并且可以包括对存储函数的调用),然后使用这些值调用过程.

我在下面编写了一个语法上有效的样板代码示例,并附有注释来解释每个组件正在做什么.除了被要求做一些"仅仅因为"之外,我不喜欢的事情很少 - 所以一切都(希望)得到了解释.

您提到使用多个值调用过程,因此本示例使用2.

请注意,由于某种原因,发生她的事件按特定顺序排列.必须首先声明变量,必须在继续处理程序之前声明游标,并且循环必须遵循所有这些.这给人的印象是,这里存在一些相当极端的不灵活性,但实际情况并非如此.您可以通过在程序正文中嵌套BEGIN... END块内的其他代码来重置排序; 例如,如果你需要在循环中使用第二个游标,你只需在循环中声明它,在另一个BEGIN...内END.

DELIMITER $$

DROP PROCEDURE IF EXISTS `my_proc` $$
CREATE PROCEDURE `my_proc`(arg1 INT) -- 1 input argument; you might not need one
BEGIN

-- from http://stackoverflow.com/questions/35858541/call-a-stored-procedure-from-the-declare-statement-when-using-cursors-in-mysql

-- declare the program variables where we'll hold the values we're sending into the procedure;
-- declare as many of them as there are input arguments to the second procedure,
-- with appropriate data types.

DECLARE val1 INT DEFAULT NULL;
DECLARE val2 INT DEFAULT NULL;

-- we need a boolean variable to tell us when the cursor is out of data

DECLARE done TINYINT DEFAULT FALSE;

-- declare a cursor to select the desired columns from the desired source table1
-- the input argument (which you might or might not need) is used in this example for row selection

DECLARE cursor1 -- cursor1 is an arbitrary label, an identifier for the cursor
 CURSOR FOR
 SELECT t1.c1, 
        t1.c2
   FROM table1 t1
  WHERE c3 = arg1; 

-- this fancy spacing is of course not required; all of this could go on the same line.

-- a cursor that runs out of data throws an exception; we need to catch this.
-- when the NOT FOUND condition fires, "done" -- which defaults to FALSE -- will be set to true,
-- and since this is a CONTINUE handler, execution continues with the next statement.   

DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

-- open the cursor

OPEN cursor1;

my_loop: -- loops have to have an arbitrary label; it's used to leave the loop
LOOP

  -- read the values from the next row that is available in the cursor

  FETCH NEXT FROM cursor1 INTO val1, val2;

  IF done THEN -- this will be true when we are out of rows to read, so we go to the statement after END LOOP.
    LEAVE my_loop; 
  ELSE -- val1 and val2 will be the next values from c1 and c2 in table t1, 
       -- so now we call the procedure with them for this "row"
    CALL the_other_procedure(val1,val2);
    -- maybe do more stuff here
  END IF;
END LOOP;

-- execution continues here when LEAVE my_loop is encountered;
-- you might have more things you want to do here

END $$

DELIMITER ;