SQL case 0 然后 NULL

Question

I wanna get NULL when the number in my table is 0. Can I achieve this using SQL?

SELECT ID, 
       Firstname, 
       Lastname, 
       CASE Number 
         WHEN 0 THEN NULL 
       END
  FROM tPerson

Error:

At least one of the result expressions in a CASE specification must be an expression other than the NULL constant.

Thanks in advance!

Answer 1

As others have mentioned you forgot to tell your CASE statement to return the number in case the number is not null.

However in SQL Server you can use NULLIF, which I consider more readable:

select 
  id, 
  firstname, 
  lastname, 
  nullif(number, 0) as number
from tperson;

If you want to stick to standard SQL then stay with CASE:

case when number = 0 then null else number end as number

Answer 2

May be you need ELSE :

SELECT 
  ID, Firstname, Lastname CASE Number WHEN 0 THEN NULL ELSE Number END
FROM tPerson

Answer 3

SELECT ID, Firstname, Lastname,
 CASE WHEN Number!=0 THEN Number END 
FROM tPerson

Answer 4

You can simply use IIF() with sql server 2012 and above

SELECT ID, 
       Firstname, 
       Lastname, 
       IIF(Number = 0, NULL, Number) as Number 
       END
FROM tPerson

Answer 5

Try:

SELECT ID, Firstname, 
   Lastname, 
   CASE Number WHEN 0 THEN NULL ELSE Number END 
FROM tPerson

Answer 6

在 MySQL 中，您还可以使用if ：

select if(number = 0, null, number) ...