Conditional Filtering in SQL

Assume I need to select a set of data based on the following criteria.

  • If the @Active-Items-Only flag is set, then select only the active items
  • otherwise select all active and non-active items.
DECLARE @ActiveOnly bit = 1; -- select only active

SELECT [HotelContractID]
  FROM [dbo].[RoomAllocation]
  WHERE [HotelContractID] = 124 AND
    -- if active only selected, 
    -- check only active = 1 rows in the table and return 1
    WHEN  @ActiveOnly = 1 AND (Active = 1) THEN 1 
    -- if active and inactive both selected, 
    -- check for both active = 1 and active = 0 rows in the table and return 1
    WHEN  @ActiveOnly = 0 AND (Active = 1 OR Active = 0) THEN 1
  END) = 1 -- 1=1 where conditional always true. magic happens in WHEN condition.

When you set @ActiveOnly = 1, it gives only the active ones.
When you set @ActiveOnly = 0, it gives only the active and inactive both.

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