mysql - 如何将查询结果存储到变量中并多次使用它？

Question

我有一个查询(触发)，如下所示:

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

如您所见，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，如何将以下查询的结果存储到变量中:

SELECT active FROM users WHERE id = new.author_id;

然后将其用于如下条件:

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？

Answer 1

声明一个 local variable 并使用 select 语句的输出来设置它。

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