SQL Server：CASE不起作用

Question

SELECT 
   a.componentId, a.uniqueCode, 
   'sd'= CASE 
            WHEN RTRIM(LTRIM(b.name)) IS NULL OR RTRIM(LTRIM(b.uniqueCode)) IS NULL 
               THEN isnull(b.uniqueCode,'')+isnull(b.name,'') 
            WHEN RTRIM(LTRIM(b.name)) IS NULL AND RTRIM(LTRIM(b.uniqueCode)) IS NULL
               THEN isnull(b.uniqueCode,'')+isnull(b.name,'')
            ELSE b.uniqueCode + '(' + (b.name) + ')'
    END, 
    a.specialization 
FROM Doctors a 
LEFT OUTER JOIN Territories b ON a.locationId = b.componentId;

Suppose b.uniqueCode = T003 and b.name = Dhanmondi 01 , then sd should be T003(Dhanmondi 01) .

Now if b.name = NULL then sd should be T003 , but my query result shows T003() .

What is wrong my T-SQL query?

Answer 1

Are you sure that b.name is null ? If it has an empty string instead of null you would have the result you see. BTW, the rtrim/ltrim stuff is totally unnecessary when checking with is null and your second when will never happen because you will always end up in the first when if either column is null .

This will treat empty strings as null:

SELECT a.componentId, a.uniqueCode, 'sd'=
        CASE 
            WHEN nullif(b.name, '') IS NULL OR nullif(b.uniqueCode, '') IS NULL 
            THEN isnull(b.uniqueCode,'')+isnull(b.name,'') 
            ELSE b.uniqueCode + '(' + (b.name) + ')'
        END , a.specialization 
FROM Doctors a LEFT OUTER JOIN Territories b ON a.locationId = b.componentId;

Answer 2

Let's sort some basics out first...

Your second WHEN is impossible to reach, since the earlier WHEN will always be true (either null) before the second WHEN (both null).

RTRIM() and LTRIM() will only return NULL if the argument is NULL , so these two condition expressions are identical:

• RTRIM(LTRIM(b.name)) IS NULL
• b.name IS NULL

Removing redundant code, including the unreachable WHEN , will let you simplify your code considerably:

CASE
    WHEN b.name IS NULL OR b.uniqueCode IS NULL 
        THEN isnull(b.uniqueCode,'') + isnull(b.name,'')
    ELSE b.uniqueCode + '(' + b.name + ')'
END

Now that we can read it...

The most likely explanation is that b.name is blank , not NULL .

Answer 3

In SQL and all of the popular SQL products - except Oracle - a NULL and an empty string '' are two different things. So, you should be checking both options:

SELECT a.componentId, a.uniqueCode, 
    CASE 
        WHEN b.name IS NULL OR b.name = ''
            THEN COALESCE(b.uniqueCode, '')
        WHEN b.uniqueCode IS NULL OR b.uniqueCode = ''
            THEN b.name
            ELSE b.uniqueCode + '(' + b.name + ')'
    END AS sd
     , a.specialization 
...

or to remove leading and trailing spaces:

    CASE 
        WHEN b.name IS NULL OR RTRIM(LTRIM(b.name)) = ''
            THEN COALESCE(RTRIM(LTRIM(b.uniqueCode)), '')
        WHEN b.uniqueCode IS NULL OR RTRIM(LTRIM(b.uniqueCode)) = ''
            THEN RTRIM(LTRIM(b.name))
            ELSE RTRIM(LTRIM(b.uniqueCode)) + '(' 
               + RTRIM(LTRIM(b.name)) + ')'
    END AS sd