MYSQL |服务提供商 | CURSOR - 将光标获取到变量 return null

Question

我想：

创建临时 table.
将部分数据插入临时 table。
运行在 temporary.user_id 字段上循环。
在数据操作和计算后更新每一行。

第 3 步的问题，我从游标中得到 user_id=NULL 而不是一个整数。

CREATE PROCEDURE user_demo_sp()
BEGIN
  DECLARE done INT DEFAULT FALSE;
  DECLARE current_user INT;
  DECLARE cur CURSOR FOR SELECT user_id FROM users_temp; -- Cursor on temp table 
  DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

-- Create a table
DROP temporary table if exists `users_temp` ;
CREATE temporary table `users_temp` (
user_id INT(11) NOT NULL,
aggregation_column INT(11) NOT NULL
);

-- Fill table
INSERT INTO users_temp SELECT user_id from users where condition ="condition";

  OPEN cur;

  read_loop: LOOP
    FETCH cur INTO current_user;
    IF done THEN
      LEAVE read_loop;
    END IF;
   select current_user; -- Return NULL

  END LOOP;

  CLOSE cur;

END;

Answer 1

you need to fill your temp table before declaring the cursor on it (just use nested Begin...END blocks):

CREATE PROCEDURE user_demo_sp()
BEGIN
  DECLARE done INT DEFAULT FALSE;
  DECLARE current_user INT;
   temp table 
  DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

-- Create a table
DROP temporary table if exists `users_temp` ;
CREATE temporary table `users_temp` (
user_id INT(11) NOT NULL,
aggregation_column INT(11) NOT NULL
);

-- Fill table
INSERT INTO users_temp SELECT user_id from users where condition ="condition";
  Begin
  DECLARE cur CURSOR FOR SELECT user_id FROM users_temp; -- Cursor on
  OPEN cur;

  read_loop: LOOP
    FETCH cur INTO current_user;
    IF done THEN
      LEAVE read_loop;
    END IF;
   select current_user; -- Return NULL

  END LOOP;

  CLOSE cur;
  End;
END;

Also in scenarios like this actually you don't need a temp table you can declare the cursor on the select which you used to fill temptale

MYSQL |服务提供商 | CURSOR - 将光标获取到变量 return null

MYSQL | SP | CURSOR - Fetch cursor into variable return null

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