Question

目前我不知道如何为SQL Server编写这个SQL语句。

我有两张桌子：

客户：

ID | Name   | Prename
----------------------
1    Miller   Thomas
....

步骤：

ID | FK_customer | step | created
------------------------------------
1    1             A      2010-02-03
2    1             B      2011-09-12
....

如果我尝试加入，我就明白了：

Name   | A_date     | B_date
----------------------------------
Miller   2010-02-03   NULL
Miller   NULL         2011-09-12

我想要的是：

Name   | A_date     | B_date
---------------------------------
Miller   2010-02-03   2011-09-12

有人能给我看灯吗？

Answer 1

您可以使用条件聚合：

if(mysql_num_rows($getphotoToGuess ) > 0){
    // do something
}

Answer 2

SELECT c.Name, A.A_date, B.B_date
FROM Customer c
CROSS APPLY
(
    SELECT MAX(created) AS A_date
    FROM steps s
    WHERE s.FK_customer  = c.Id
    AND s.step = 'A'
)AS A
CROSS APPLY
(
    SELECT MAX(created) AS B_date
    FROM steps s
    WHERE s.FK_customer  = c.Id
    AND s.step = 'B'
)B

在SQL中分组

2 个答案: