t sql select 语句中的子查询

Question

我有一个列出用户的查询，但它需要一个子查询来了解他们今天是否有空。我需要第四列 'Availability' 来遍历每个用户并显示他们是否有空或显示空值。我已经尝试了所有我能想到的子查询、游标等，但没有任何乐趣。欢迎任何指点！

SELECT inter.authno,
       inter.FirstName,
       inter.Surname,
       COALESCE(( 
                 Select at.typeName as [Availability]
                 FROM [database].[dbo].[Interviewer] inter 
                 full join [database].[dbo].[availability] av 
                 on inter.authno = av.authno
                 full join [database].[dbo].[availability_days] ad 
                 on av.availID = ad.availID
                 full join [database].[dbo].[availibiltyType] at
                 on av.typeID = at.typeid
                 where exists(
                      select authno 
                      from [database].[dbo].[Interviewer]
                 )
                 and ad.actualDay = '2015-05-21'
                 ), null ) AS [Availability]

 FROM [database].[dbo].[Interviewer] inter

查询给出了以下结果，但它应该只显示 Available for Harry Kane，其余的应该为空。

authno FirstName Surname Availability
-------------------------------------
10     Minch     Yoda    Available 
11     Darth     Vadar   Available 
12     Darth     Maul    Available 
14     Obi Wan   Kenobi  Available
15     Qui-Gon   Jinn    Available
16     Darth     Sidious Available
17     Boba      Fett    Available
24     Harry     Kane    Available
39     mark      o'neill Available

我也尝试了下面友情提供的代码建议，它提供了一些我需要的结果，但它显示了所有结果，而不是今天的可用性类型。

        SELECT 
    inter.authno,
    inter.FirstName,
    inter.Surname,
    at.typeName as [Availability]

    FROM [database].[dbo].[Interviewer] inter 

    left JOIN [database].[dbo].[availability] av
    on inter.authno = av.authno

    left JOIN [database].[dbo].[availability_days] ad 
    on av.availID = ad.availID 
    and ad.actualDay = '2015-07-21' 

    left JOIN [database].[dbo].[availibiltyType] at 
    on av.typeID = at.typeid

输出：

  +----+---------+-----------+--------------+
        | 10 |  Minch  |   Yoda    |     NULL     |
        +----+---------+-----------+--------------+
        | 11 | Darth   | Vadar     | NULL         |
        | 12 | Darth   | Maul      | NULL         |
        | 13 | Luke    | Skywalker | NULL         |
        | 14 | Obi Wan | Kenobi    | NULL         |
        | 15 | Qui-Gon | Jinn      | Annual Leave |
        | 16 | Darth   | Sidious   | NULL         |
        | 17 | Boba    | Fett      | UO           |
        | 17 | Boba    | Fett      | Available    |
        | 18 | test22  | test33    | NULL         |
        | 19 | test7   | test7     | NULL         |
        | 22 | Bob     | Marley    | NULL         |
        | 23 | JO      | JO        | NULL         |
        | 24 | Harry   | Kane      | Annual Leave |
        | 24 | Harry   | Kane      | Available    |
        | 24 | Harry   | Kane      | Available    |
        | 24 | Harry   | Kane      | Annual Leave |
        | 24 | Harry   | Kane      | Annual Leave |
        | 24 | Harry   | Kane      | NW           |
        | 24 | Harry   | Kane      | NW           |
        | 24 | Harry   | Kane      | Available    |
        | 39 | mark    | o'neill   | US           |
        +----+---------+-----------+--------------+

我还尝试了下面的方法，它得到了我需要的确切结果，我需要显示所有用户，无论他们是否在 table 中有日期。即，如果我将日期更改为最后一次，Harry Kane 就会消失。

        SELECT 
    inter.authno,
    inter.FirstName,
    inter.Surname,
    at.typeName as [Availability]

    FROM [database].[dbo].[Interviewer] inter 

    left JOIN [database].[dbo].[availability] av
    on inter.authno = av.authno

    left JOIN [database].[dbo].[availability_days] ad 
    on av.availID = ad.availID 

    left JOIN [database].[dbo].[availibiltyType] at 
    on av.typeID = at.typeid

            where ad.actualDay = '2015-05-21'or ad.actualDay is null

今天的产出：

    +--------+-----------+-----------+--------------+
    | authno | FirstName |  Surname  | Availability |
    +--------+-----------+-----------+--------------+
    |     10 | Minch     | Yoda      | NULL         |
    |     11 | Darth     | Vadar     | NULL         |
    |     12 | Darth     | Maul      | NULL         |
    |     13 | Luke      | Skywalker | NULL         |
    |     14 | Obi Wan   | Kenobi    | NULL         |
    |     16 | Darth     | Sidious   | NULL         |
    |     18 | test22    | test33    | NULL         |
    |     19 | test7     | test7     | NULL         |
    |     22 | Bob       | Marley    | NULL         |
    |     23 | JO        | JO        | NULL         |
    |     24 | Harry     | Kane      | Available    |
    +--------+-----------+-----------+--------------+

Output for 2015-05-10

+--------+-----------+-----------+--------------+
| authno | FirstName |  Surname  | Availability |
+--------+-----------+-----------+--------------+
|     10 | Minch     | Yoda      | NULL         |
|     11 | Darth     | Vadar     | NULL         |
|     12 | Darth     | Maul      | NULL         |
|     13 | Luke      | Skywalker | NULL         |
|     14 | Obi Wan   | Kenobi    | NULL         |
|     16 | Darth     | Sidious   | NULL         |
|     18 | test22    | test33    | NULL         |
|     19 | test7     | test7     | NULL         |
|     22 | Bob       | Marley    | NULL         |
|     23 | JO        | JO        | NULL         |
+--------+-----------+-----------+--------------+

Answer 1

没有看到您的 table 结构这是一个猜测，但是是一个有根据的猜测。试试这个：

SELECT inter.authno,
       inter.FirstName,
       inter.Surname,
       at.typeName as [Availability]
 FROM [database].[dbo].[Interviewer] inter 
 LEFT JOIN [database].[dbo].[availability] av on inter.authno = av.authno
 LEFT JOIN [database].[dbo].[availability_days] ad on av.availID = ad.availID and ad.actualDay = '2015-05-21'
 LEFT JOIN [database].[dbo].[availibiltyType] at on av.typeID = at.typeid

对于您以后可能遇到的 sql 问题，请包括相关的 tables DDL, some sample data (preferably as DML 语句）和所需的输出。

Answer 2

如果我没理解错的话，您需要一个与您的查询版本相关的子查询：

SELECT inter.authno,
       inter.FirstName,
       inter.Surname,
       (Select at.typeName as [Availability]
        FROM [database].[dbo].[availability] av join
             [database].[dbo].[availability_days] ad 
             on av.availID = ad.availID join
             [database].[dbo].[availibiltyType] at
             on av.typeID = at.typeid
        where inter.authno = av.authno and ad.actualDay = '2015-05-21'
       ) AS [Availability]
FROM [database].[dbo].[Interviewer] inter;

一些注意事项：

COALESCE(<x>, NULL) 没有意义。只需使用 <X>
对于子查询，您应该使用 IFNULL() 而不是 COALESCE()，因为 SQL 服务器有（我认为是）有缺陷的 COALESCE() 实现。
您的子查询需要与外部查询相关联。
我不知道 EXISTS 子句应该做什么。如果 table 有任何行，那么它总是 return TRUE。
子查询中没有full joins的原因。
我希望您的版本 return 错误 "subquery returns more than one row"。

t sql select 语句中的子查询

Sub query in t sql select statement

sql

tsql

stored-procedures

sql-server-2008-r2