WHERE子句中的CASE语句（SQL Server）

Question

I am using Case statement in WHERE clause for SQL Server. However, the values I have in THEN clause is a list of integer. Is there any other way of doing this in a WHERE clause? OrderIds are in drop-down list, so either 30, 40 or 50 is selected of it none is selected, then orderID IN (30, 40, 50). PS I can't do @OrderID IS NULL otherwise it will search for every orderid in the database. So either one value or default (30,40,50)

WHERE 
    1 = 1
    AND [Order].[ORDERID] IN 
        (CASE WHEN @ORDERID IS NOT NULL
            THEN @ORDERID 
        ELSE
            THEN ('30,40,50')
        END)

I keep getting an error

Conversion failed when converting the varchar value '30,40,50' to data type int

Answer 1

Do not use a case expression . Just use basic logic:

WHERE 1 = 1 AND
      (@OrderId IS NULL OR [Order].OrderId in (30, 40, 50))

I would also advise you to name your tables so they do not conflict with SQL keywords. Your table could be named Orders for instance.

Also, I assume the string representation for the list is unnecessary. Otherwise, that introduces other issues (if you are representing a list as a string).

EDIT:

I'm worried that the actual logic you want is:

WHERE 1 = 1 AND
      ((@OrderId IS NULL AND [Order].OrderId in (30, 40, 50)) OR
       ([Order].OrderId = @OrderId)
      )

This works, as long as you have a single value in @OrderId .

Answer 2

CASE expressions result in values . You can't use them to produce expressions , such as the value list expression you're trying to use. You need to re-think how you structure this so you can just use a value.

One way to do this is to split the case expression so each possible WHEN result is it's own condition, and the alternative result from each condition will produce true :

WHERE 
    1 = 1
    AND [Order].[ORDERID] = coalesce(@ORDERID, [Order].[ORDERID])
    AND case when @orderid is null then [Order].[ORDERID] ELSE 30 end IN (30, 40, 50)

There's usually a simpler way to write the expression, but this illustrates a reliable way to make the conversion from incorrect CASE to correct WHERE.

Answer 3

If your numbers are a comma separated string of numbers , you can use this code:

DECLARE @LIST VARCHAR(200)
SET @LIST = '30, 40, 50'

---------------------------
WHERE 1 = 1 AND
     (
      @OrderId IS NULL
      OR
      [Order].OrderId in (SELECT * FROM dbo.SplitStrings_Moden(@LIST,N','))
     )

To use the above code you need to define the following function in your DB to get a Table from comma separated string of numbers:

CREATE FUNCTION dbo.SplitStrings_Moden
(
   @List NVARCHAR(MAX),
   @Delimiter NVARCHAR(255)
)
RETURNS TABLE
WITH SCHEMABINDING AS
RETURN
  WITH E1(N)        AS ( SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 
                         UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 
                         UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1),
       E2(N)        AS (SELECT 1 FROM E1 a, E1 b),
       E4(N)        AS (SELECT 1 FROM E2 a, E2 b),
       E42(N)       AS (SELECT 1 FROM E4 a, E2 b),
       cteTally(N)  AS (SELECT 0 UNION ALL SELECT TOP (DATALENGTH(ISNULL(@List,1))) 
                         ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) FROM E42),
       cteStart(N1) AS (SELECT t.N+1 FROM cteTally t
                         WHERE (SUBSTRING(@List,t.N,1) = @Delimiter OR t.N = 0))
  SELECT Item = SUBSTRING(@List, s.N1, ISNULL(NULLIF(CHARINDEX(@Delimiter,@List,s.N1),0)-s.N1,8000))
    FROM cteStart s;