How can I make this SELECT CASE run faster?

Question

Can anyone help me to modify the sql below to make it run faster? Thanks.

SELECT DISTINCT B.CLT_NBR ,
       CASE 
          WHEN B.CLT_NBR IN (SELECT CLT_NBR FROM A) THEN 'YES' 
          ELSE 'NO' 
       END AS CHECK  
FROM B

Answer 1

Use left join instead of a subquery:

SELECT DISTINCT B.CLT_NBR ,
       CASE 
          WHEN A.Id IS NOT NULL THEN 'YES' 
          ELSE 'NO' 
       END AS CHECK  
FROM B
LEFT JOIN A ON(B.CLT_NBR = A.CLT_NBR)

Note: instead of the A.Id I've used you need to use A's primary key.