mysql - 如何使用 UNION 合并两个具有 ORDER BY 的查询？

Question

我有两个查询，每个查询都有自己的 order by，如下所示:

查询 1:

SELECT id, name, title, content 
FROM table where match(title, content) against('anything') 
Order By title

查询 1:

SELECT id, tag, question, answer 
FROM table 
Where tag like '%anything' 
Order By tag, question

现在如何使用 UNION ALL 将它们组合起来？

Answer 1

您需要按以下方式对结果进行排序:

1. 结果类型(MATCH 或 LIKE)
2. 标题(用于 MATCH)或标签(用于 LIKE)
3. NULL(对于 MATCH)或问题(对于 LIKE)

您可以使用嵌套查询:

SELECT * FROM (
    SELECT 1 AS result_type, id, name, title, content 
    FROM table
    WHERE MATCH (title, content) AGAINST ('anything') 
    UNION ALL
    SELECT 2, id, tag, question, answer 
    FROM table 
    WHERE tag LIKE '%anything' 
) AS foobar
ORDER BY
    result_type,
    CASE result_type WHEN 1 THEN title ELSE tag END,
    CASE result_type WHEN 1 THEN NULL ELSE question END

或者您可以添加排序辅助列:

(
SELECT 1 AS sort_1, title AS sort_2, NULL     AS sort_3, id, name, title, content 
FROM table
WHERE MATCH (title, content) AGAINST ('anything') 
) UNION ALL (
SELECT 2 AS sort_1, tag   AS sort_2, question AS sort_3, id, tag, question, answer 
FROM table 
WHERE tag LIKE '%anything' 
)
ORDER BY sort_1, sort_2, sort_3