如何将查询结果存储到变量中并多次使用？

Question

我有一个查询（触发）这样的：

BEGIN  
    IF (new.edited_id IS NULL) THEN 
     IF (SELECT 1 FROM users WHERE id = new.author_id AND IFNULL((active & b'1000000' > 0), 0) < 1) THEN 
      SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = "you cannot ask anymore"; 
     ELSEIF (SELECT 1 FROM users WHERE id = new.author_id AND IFNULL((active & b'10000000' > 0), 0) < 1) THEN 
      SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = "you cannot answer anymore"; 
     END IF; 
    ELSE 
     IF (SELECT 1 FROM users WHERE id = new.author_id AND IFNULL((active & b'100000000' > 0), 0) < 1) THEN 
      SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = "you cannot edit anymore"; 
     END IF; 
END 

正如你看到的，这些内部IF语句的条件几乎相同。那么我该如何改进呢？

我的意思是，我怎么可以存储下面的查询到一个变量的结果：

SELECT active FROM users WHERE id = new.author_id; 

，然后用它为这样的那些条件：

IF (IFNULL((@variable & b'1000000' > 0), 0) < 1) THEN 
IF (IFNULL((@variable & b'10000000' > 0), 0) < 1) THEN 
IF (IFNULL((@variable & b'100000000' > 0), 0) < 1) THEN 

我该如何处理呢？

Answer 1

声明local variable并将其设置为select语句的输出。

DECLARE v_active bit(10); 
SET v_active := (SELECT active FROM users WHERE id = new.author_id);