Question

SELECT DISTINCT ID FROM (SELECT * FROM tbl1 UNION 
SELECT * FROM tbl2 UNION 
SELECT * FROM tbl3 UNION 
SELECT * FROM tbl4 ORDER BY total_hits DESC) AS sumtbl LIMIT 50;

此查询工作正常，并选择按total_hits DESC排序的唯一ID，问题是如何返回total_hits列也具有Id的唯一性？

Answer 1

SELECT ID, SUM(total_hits) 
FROM (
    SELECT * FROM tbl1 UNION 
    SELECT * FROM tbl2 UNION 
    SELECT * FROM tbl3 UNION 
    SELECT * FROM tbl4
) AS sumtbl
GROUP BY ID
ORDER BY SUM(total_hits) DESC
LIMIT 50;

Answer 2

如果你想要所有表中的所有id的total_hits FROM，你需要做一个sum / group by。不确定这是不是你问的问题，因为问题很模糊......

SELECT DISTINCT id, sum(total_hits) total_hits
FROM (SELECT * FROM tbl1 UNION 
     SELECT * FROM tbl2 UNION 
     SELECT * FROM tbl3 UNION 
     SELECT * FROM tbl4) AS sumtbl 
GROUP BY id
ORDER BY total_hits DESC
LIMIT 50

此外，不要使用select *，因为这是不好的做法，尤其是如果您要将列添加到其中一个表而不是其他表，则整个查询将会中断。

Answer 3

<强>更新

在你的情况下你可以做到

SELECT ID, MAX(total_hits) as max_hits
FROM (
   SELECT * FROM tbl1 UNION 
   SELECT * FROM tbl2 UNION 
   SELECT * FROM tbl3 UNION 
   SELECT * FROM tbl4
)sumtbl
GROUP BY ID
ORDER BY max_hits DESC
LIMIT 50

注意：在派生查询中不需要ORDER BY，它会转到上面的

另外，如果你是的话会更好 SELECT id, total_hits FROM tbl1 UNION ALL SELECT id, total_hits FROM tbl2等，而不是从派生查询中的表中选择所有字段。

Mysql在选择其他列时不同

3 个答案: