Optimize multiple query separated by condition - sql

Question

I have a stored procedures with three different queries, that querys return values depending of received variable.
They basically return same data, just change WHERE clauses:
Query:
IF #DesignType = 'BDCD'
BEGIN
SELECT
[DT].[DesignTypeGuid]
, [DT].[Name]
, [DT].[Abbreviation]
, CONVERT(BIT , IIF([DT].[DesignTypeGuid] = #ContractedDocument , 1 , 0)) AS [EnforceBaseOnPrevious]
, [DT].[Order]
FROM [DesignType] AS [DT]
WHERE [DT].[IsActive] = 1
AND ([DT].[DesignTypeGuid] != IIF(#DesignTypeGuid = #ContractedDocument , #BidDocument , #ContractedDocument))
AND [DT].[DesignTypeGuid] != #ChangeOrder
AND [DT].[DesignTypeGuid] != #AddedPart
ORDER BY
[DT].[Order]
END
ELSE
BEGIN
IF #DesignType = 'CO'
BEGIN
SELECT
[DT].[DesignTypeGuid]
, [DT].[Name]
, [DT].[Abbreviation]
, 0 AS [EnforceBaseOnPrevious]
, [DT].[Order]
FROM [DesignType] AS [DT]
WHERE [DT].[IsActive] = 1
AND [DT].[DesignTypeGuid] = #ChangeOrder
ORDER BY
[DT].[Order]
END
ELSE
BEGIN
IF #DesignType = 'AP'
BEGIN
SELECT
[DT].[DesignTypeGuid]
, [DT].[Name]
, [DT].[Abbreviation]
, 0 AS [EnforceBaseOnPrevious]
, [DT].[Order]
FROM [DesignType] AS [DT]
WHERE [DT].[IsActive] = 1
AND [DT].[DesignTypeGuid] = #AddedPart
ORDER BY
[DT].[Order]
END
Is there any way to optimize this and do it in a simple SELECT instead do 3 differents depending of DesignType variable? Regards

Answer 1

Not sure about the performance , but the query could definitely be written as
SELECT
[DT].[DesignTypeGuid]
, [DT].[Name]
, [DT].[Abbreviation]
, CASE #DesignType WHEN 'BDCD' THEN CONVERT(BIT , IIF([DT].[DesignTypeGuid] = #ContractedDocument , 1 , 0)) ELSE 0 END AS [EnforceBaseOnPrevious]
, [DT].[Order]
FROM [DesignType] AS [DT]
WHERE [DT].[IsActive] = 1
AND (
(
#DesignType = 'BDCD' AND [DT].[DesignTypeGuid] NOT IN ( IIF(#DesignTypeGuid = #ContractedDocument , #BidDocument , #ContractedDocument),#ChangeOrder,#AddedPart)
)
OR
(
#DesignType = 'CO' AND [DT].[DesignTypeGuid] = #ChangeOrder
)
OR
(
#DesignType = 'AP' AND [DT].[DesignTypeGuid] = #AddedPart
)
)
ORDER BY
[DT].[Order]