如何从SQL Server 2008中的where子句检查表中数据的存在？

Question

Suppose I have a table with columns user_id , name and the table contains data like this:

user_id   name
-------   -----
sou       souhardya
cha       chanchal
swa       swapan
ari       arindam
ran       ranadeep

If I want to know these users ( sou , cha , ana , agn , swa ) exists in this table or not then I want output like this:

user_id    it exists or not
-------    -----------------
sou            y
cha            y
ana            n
agn            n
swa            y

As ana and aga do not exist in the table it must show "n" (like the above output).

Answer 1

Assuming your existing checklist is not on the database, you will have to assemble a query containing those. There are many ways of doing it. Using CTEs, it would look like this:

with cte as
(
select 'sou' user_id
union all
select 'cha'
union all
select 'ana'
union all
select 'agn'
union all
select 'swa'
)
select 
  cte.user_id,
  case when yt.user_id is null then 'n' else 'y' end
from cte
left join YourTable yt on cte.user_id = yt.user_id

This also assumes user_id is unique.

Here is the SQLFiddle with the proof of concept: http://sqlfiddle.com/#!3/e023a0/4

Answer 2

Assuming you're just testing this manually:

DECLARE @Users TABLE
(
    [user_id] VARCHAR(50)
)

INSERT INTO @Users 
SELECT 'sou'
UNION SELECT 'cha'
UNION SELECT 'ana'
UNION SELECT 'agn'
UNION SELECT 'swa'



SELECT a.[user_id]
    , [name]
    , CASE
        WHEN b.[user_id] IS NULL THEN 'N'
        ELSE 'Y'
        END AS [exists_or_not]
FROM [your_table] a
LEFT JOIN @Users b
    ON a.[user_id] = b.[user_id]

Answer 3

You didn't provide quite enough information to provide a working example, but this should get you close:

select tbl1.user_id, case tbl2.user_id is null then 'n' else 'y' end
from   tbl1 left outer join tbl2 on tbl1.user_id = tbl2.user_id

Answer 4

;with usersToCheck as
(
          select 'sou' as userid
    union select 'cha'
    union select 'ana'
    union select 'agn'
    union select 'swa'
)
select utc.userid, 
(case when exists ( select * from usersTable as ut where ut.user_id = utc.userid) then 'y' else 'n' end)
from usersToCheck as utc