Question

使用SELECT DISTINCT（）和ORDER BY时遇到问题... 这是我的SQL：

SELECT DISTINCT(t2)
FROM Table1 t1
JOIN Table2 t2 ON t1.t2 = t2.id
JOIN Table3 t3 ON t1.t3 = t3.id
JOIN Table4 t4 ON t2.t4 = t4.id
JOIN Table5 t5 ON t2.t5 = t5.id
JOIN Table6 t6 ON t2.t6 = t6.id
ORDER BY t4.date DESC

但这是错的......你有什么想法吗？

提前致谢！ =）

Answer 1

在SELECT DISTINCT查询中，您只能按SELECT中的列进行排序。毕竟，date的值应该用于排序？

好的，我猜可以。。。最大值。所以，使用聚合：

SELECT t2
FROM Table1 t1 JOIN
     Table2 t2 ON t1.t2 = t2.id JOIN
     Table3 t3 ON t1.t3 = t3.id JOIN
     Table4 t4 ON t2.t4 = t4.id JOIN
     Table5 t5 ON t2.t5 = t5.id JOIn
     Table6 t6 ON t2.t6 = t6.id
GROUP BY t2
ORDER BY MAX(t4.date) DESC;

Answer 2

你的t2只是你桌子的别名，不能这样做：

应该是这样的：

SELECT DISTINCT t2.*,t3.*,t4.*
FROM Table1 t1
JOIN Table2 t2 ON t1.id = t2.id
JOIN Table3 t3 ON t1.id = t3.id
JOIN Table4 t4 ON t2.id = t4.id
JOIN Table5 t5 ON t2.id = t5.id
JOIN Table6 t6 ON t2.id = t6.id
ORDER BY t4.date DESC

如果你使用*，你必须小心使用相同的列名，因为它会返回一个含糊不清的错误..你可以简单地喜欢t3.column1等等。

Answer 3

只需进行子查询

SELECT * FROM 
    (
    SELECT DISTINCT *
    FROM Table1 t1
    JOIN Table2 t2 ON t1.t2 = t2.id
    JOIN Table3 t3 ON t1.t3 = t3.id
    JOIN Table4 t4 ON t2.t4 = t4.id
    JOIN Table5 t5 ON t2.t5 = t5.id
    JOIN Table6 t6 ON t2.t6 = t6.id
    )
ORDER BY t4.date DESC

使用带有ORDER BY的SELECT DISTINCT（）时出错

3 个答案: