IN in the result expression in the CASE THEN expression

Question

Can i use INin CASE..THEN?

WHERE
   record.field =
      CASE
          WHEN @flag = 1 THEN a
          WHEN @flag = 2 THEN IN (b, c)
      END

Or how to rewrite such a condition?

Answer 1

Sorry, but no:

WHERE
    (@flag = 1 AND record.field = a)
    OR
    (@flag = 2 AND record.field IN (b, c))

Answer 2

to try:

WHERE (@flag = 1 AND record.field = a )
    OR (@flag = 2 AND record.field IN (b, c))

it might be better to try JOIN in value and use an index:

DECLARE @Table (ValueOf  int)
INSERT INTO @Table ((ValueOf)
    SELECT a WHERE @flag = 1
    UNION SELECT b WHERE @flag = 2
    UNION SELECT c WHERE @flag = 2

SELECT
    ....
    FROM ...           x
    INNER JOIN @Table  t ON x...=t.ValueOf