Question

I have a table :

id | Val
____________
1  | a
2  | s
3  | e
4  | f
5  | h

I have a query which accepts 2 params :

@id1 int
@id2 int

This query has 2 internal variables :

@val1 int
@val2 int

I need to set values into those variables : like –

select @val1=val from where id=@id1
select @val2=val from where id=@id2

I want to do it with one query…. I’ve tried:

select @val1=val , @val2=val  
from  table
where id=@id2 or  id=@id1

The problem is :

@val1 should set to val only when id=@id1

and

@val2 should set to val only when id=@id2

(what about @val2 when id=@id1 ? what value will it get ?)

How can I write those 2 queries in 1 ?

Answer 1

SELECT 
      @val1=CASE WHEN id=@id1 THEN Val ELSE @val1 END
    , @val2=CASE WHEN id=@id2 THEN Val ELSE @val2 END
FROM table
WHERE ID IN (@id1, @id2)

To test it out:

CREATE TABLE #tmp (ID INT, VAL CHAR(1))
INSERT INTO #tmp VALUES (1,'a')
INSERT INTO #tmp VALUES (2,'s')
INSERT INTO #tmp VALUES (3,'e')
INSERT INTO #tmp VALUES (4,'f')
INSERT INTO #tmp VALUES (5,'h')

DECLARE @id1 INT=1
DECLARE @id2 INT=4

DECLARE @val1 CHAR(1)
DECLARE @val2 CHAR(1)

SELECT 
      @val1=CASE WHEN id=@id1 THEN Val ELSE @val1 END AS Val1
    , @val2=CASE WHEN id=@id2 THEN Val ELSE @val2 END AS Val2
FROM #tmp
WHERE ID IN (@id1, @id2)

SELECT @val1, @val2  --Returns a, f

DROP TABLE #tmp