Question

我有一个有两列的表。我想比较第一列的每一行与第二列中的所有行。如果匹配，我需要在第3列中插入yes，否则我需要插入no。

First second
A      B
C      D
E      A
X      c

输出应为

First second  yesOrno
A      B         yes
C      D         yes
E      A         NO
X      c         NO

Answer 1

使用相同表格的EXISTS。

UPDATE T1 SET
    ThirdColumn = CASE WHEN EXISTS (
        SELECT
            'a SecondColumn match exists'
        FROM
            YourTable AS T2
        WHERE 
            T1.FirstColumn = T2.SecondColumn) THEN 'Yes' ELSE 'No' END
FROM
    YourTable AS T1

Answer 2

SELECT 
     First, Second,
     CASE WHEN EXISTS (
        SELECT * FROM Table t2 
        WHERE t2.Second = t1.First) 
        THEN 'Yes' ELSE 'No' END AS YesOrNo
FROM
     Table t1

Answer 3

你可以通过自我加入获得它，如下所示

  select T1.First,T1.second,(case when T2.second is null then 'no' else 'yes' end) as yesOrno from T as T1 left join T as T2
    on T1.First=t2.second

检查sql小提琴：SQL Fiddle

Answer 4

你可以这样做：

declare @t table (
    C1 char(1),
    C2 char(1)
)

insert  @t
values  ('A','B'),
        ('C','D'),
        ('E','A'),
        ('X','C')

select  t1.C1,t1.C2, case when t2.C2 is null then 'No' else 'Yes' end YesOrNo
from    @t t1 left join @t t2
        on t1.C1 = t2.C2

编写此基本查询的方法有很多种。

将第一列中的每一行与第二列中的所有行进行比较

4 个答案: