T-SQL CASE Clause: How to specify WHEN NULL

Question

I wrote a T-SQL Statement similar like this (the original one looks different but I want to give an easy example here):

SELECT first_name + 
    CASE last_na         


        

Answer 1

When you get frustrated trying this:

CASE WHEN last_name IS NULL THEN '' ELSE ' '+last_name END

Try this one instead:

CASE LEN(ISNULL(last_Name,''))
WHEN 0 THEN '' 
ELSE ' ' + last_name
END AS newlastName

LEN(ISNULL(last_Name,'')) measures the number of characters in that column, which will be zero whether it's empty, or NULL, therefore WHEN 0 THEN will evaluate to true and return the '' as expected.

I hope this is a helpful alternative.

I have included this test case for sql server 2008 and above:

DECLARE @last_Name varchar(50) = NULL

SELECT 
CASE LEN(ISNULL(@last_Name,''))
WHEN 0 THEN '' 
ELSE 'A ' + @last_name
END AS newlastName

SET @last_Name = 'LastName'

SELECT 
CASE LEN(ISNULL(@last_Name,''))
WHEN 0 THEN '' 
ELSE 'A ' + @last_name
END AS newlastName

Answer 2

There are plenty of solutions but none covers why the original statement doesn't work.

CASE last_name WHEN null THEN '' ELSE ' '+last_name

After the when, there is a check for equality, which should be true or false.

If one or both parts of a comparison is null, the result of the comparison will be UNKNOWN, which is treated like false in a case structure. See: https://www.xaprb.com/blog/2006/05/18/why-null-never-compares-false-to-anything-in-sql/

To avoid this, Coalesce is the best way.

Answer 3

CASE WHEN last_name IS NULL THEN '' ELSE ' '+last_name END

Answer 4

try:

SELECT first_name + ISNULL(' '+last_name, '') AS Name FROM dbo.person

This adds the space to the last name, if it is null, the entire space+last name goes to NULL and you only get a first name, otherwise you get a firts+space+last name.

this will work as long as the default setting for concatenation with null strings is set:

SET CONCAT_NULL_YIELDS_NULL ON 

this shouldn't be a concern since the OFF mode is going away in future versions of SQl Server

Answer 5

I tried casting to a string and testing for a zero-length string and it worked.

CASE 
   WHEN LEN(CAST(field_value AS VARCHAR(MAX))) = 0 THEN 
       DO THIS
END AS field 

Answer 6

The problem is that null is not considered equal to itself, hence the clause never matches.

You need to check for null explicitly:

SELECT CASE WHEN last_name is NULL THEN first_name ELSE first_name + ' ' + last_name