使用 Case 语句时获取空值

Question

I am trying to derive a column ( Level5 ) based on another columns ( Selection and IsAssetCode ).

Selection column has two types of entries - "All Asset" and "Core Asset", and IsAssetCode is 0 or 1 . IsAssetCode = 0 corresponds to "All Asset," and 1 is "Core Asset".

I am trying to separate Core and Non-core assets but I am getting extra rows with "All Assets" in Level5 .

Select *, 
   Case when Selection ='All Assets' then 'Other Assets'
        When (IsAssetCode =1 and Selection <> 'ALL ASSETS') THEN Selection
   End  as Level5
From ((Select (columns) from tbl where IsAssetCode = 0
      EXCEPT
      SELECT (Columns) FROM tbl where IsAssetCode = 1)
      Union
      Select (column) from tbl where IsAssetCode = 1
     )

Input data:

B1  Black  All Assets  0
B1  White All Assets   0
B1  Red     All Assets  0
B1  Black  Core Asset 1

Desired Output:

B1 Black    Core Asset  1
B1 White   Other Asset  2
B1 Red      Other Asset  2

Answer 1

Please always tag the RDBMS used, I assume SQL-Server.

The default value of a CASE EXPRESSION when no conditions are met is NULL , so my guess - all the rows with "ALL ASSETS" has IsAssetCode <> 1 right?

To override this, you can use the ELSE :

CASE WHEN <Cond> Then <FirstVal>
     WHEN <Cond2> Then <SecondVal>
     ELSE <IfNonOfAboveVal>
END

Or just provide a different condition to catch everything.

Answer 2

Just use COUNT() and GROUP BY to get the desired count

SELECT *, 
       CASE WHEN selection = 'All Assets' 
            THEN 'Other Assets'
            WHEN (isassetcode = 1 AND selection <> 'All Assets') 
            THEN selection
        END AS Level5,
       COUNT(*) cnt
  FROM table --or sub-query
 GROUP BY list all columns in the select that corresponds the *,
          CASE WHEN selection = 'All Assets' 
               THEN 'Other Assets'
               WHEN (isassetcode = 1 AND selection <> 'All Assets') 
               THEN selection
           END