MySQL Case 语句 - 未知列在哪里

Question

我的查询有问题，怎么了？

SELECT 
    CASE 
        WHEN cp_pessoa.score < 100 THEN 1 
        WHEN cp_pessoa.score < 300 THEN 2 
        WHEN cp_pessoa.score >= 300 THEN 3 
    END as id_ranking
FROM cp_pessoa 
    WHERE id_ranking IN (1,2);

我收到此错误:#1054 - “where 子句”中的未知列“id_ranking”

谢谢!

Answer 1

这是因为 SELECT 在调用 WHERE 之后准备结果(作为 id_ranking)。

SELECT 
    CASE 
    WHEN cp_pessoa.score < 100 THEN 1 
    WHEN cp_pessoa.score < 300 THEN 2 
    WHEN cp_pessoa.score >= 300 THEN 3 
END as id_ranking
FROM cp_pessoa 
WHERE cp_pessoa.score < 300;

这是它的工作原理(顺序):

1. FROM 子句
2. WHERE 子句
3. GROUP BY 子句
4. HAVING子句
5. SELECT子句
6. ORDER BY 子句