SQL Server IF EXISTS THEN 1 ELSE 2

问题

Using Sql Server 2012. I have a stored procedure and part of it checks if a username is in a table. If it is, return a 1, if not, return a 2. This is my code:

IF EXISTS (SELECT * FROM tblGLUserAccess WHERE GLUserName ='xxxxxxxx') 1 else 2

However, I keep receiving the below error:

Incorrect syntax near '1'.

Is this even possible with an IF EXIST?

Regards,

Michael

回答1:

If you want to do it this way then this is the syntax you're after;

IF EXISTS (SELECT * FROM tblGLUserAccess WHERE GLUserName ='xxxxxxxx') 
BEGIN
   SELECT 1 
END
ELSE
BEGIN
    SELECT 2
END

You don't strictly need the BEGIN..END statements but it's probably best to get into that habit from the beginning.

回答2:

How about using IIF?

SELECT IIF (EXISTS (SELECT 1 FROM tblGLUserAccess WHERE GLUserName ='xxxxxxxx'), 1, 2)

Also, if using EXISTS to check the the existence of rows, don't use *, just use 1. I believe it has the least cost.

回答3:

In SQL without SELECT you cannot result anything. Instead of IF-ELSE block I prefer to use CASE statement for this

SELECT CASE
         WHEN EXISTS (SELECT 1
                      FROM   tblGLUserAccess
                      WHERE  GLUserName = 'xxxxxxxx') THEN 1
         ELSE 2
       END 

回答4:

What the output that you need, select or print or .. so on.

so use the following code:

IF EXISTS (SELECT * FROM tblGLUserAccess WHERE GLUserName ='xxxxxxxx') select 1 else select 2

回答5:

You can define a variable @Result to fill your data in it

DECLARE @Result AS INT

IF EXISTS (SELECT * FROM tblGLUserAccess WHERE GLUserName ='xxxxxxxx') 
SET @Result = 1 
else
SET @Result = 2

回答6:

Its best practice to have TOP 1 1 always.

What if I use SELECT 1 -> If condition matches more than one record then your query will fetch all the columns records and returns 1.

What if I use SELECT TOP 1 1 -> If condition matches more than one record also, it will just fetch the existence of any row (with a self 1-valued column) and returns 1.

IF EXISTS (SELECT TOP 1 1 FROM tblGLUserAccess WHERE GLUserName ='xxxxxxxx') 
BEGIN
   SELECT 1 
END
ELSE
BEGIN
    SELECT 2
END

来源：https://stackoverflow.com/questions/41015307/sql-server-if-exists-then-1-else-2