How can you use NULLIF in the where clause? - sql

Question

I am trying to do something like this:
select
col_1, col_2, etc
from
table
where
col_1 = nullif('', '')
Am I doing this incorrectly? I am not getting any results back.
Edit:
My expected results are to get every record back where col_1 is NULL.
I know I can use where col_1 is null, but I am using SSIS and a variable. Sometimes the col_1 is actually NULL and sometimes it is not.
Sample data:
collaboration first_name last_name city
NULL Bob Smith Chicago
Data Migration John Smith Austin
NULL Pika Chu Houston
Production ash ketchum tokyo
Sometimes I may want to return the records where collaboration is NULL, sometimes I want to return the records where it says Production.
I'd like to use the same query, if possible, with little modification.
Edit Part 2:
I tried to experiment with this.
select
col_1, col_2, etc
from
table
where
case
when col_1 = '' then NULL
else col_1
end
But I am getting the error message:
An expression of non-boolean type specified in a context where a condition is expected, near ORDER.
Query speed it not something I am concerned with.

Answer 1

This is the query you need
select
col_1, col_2, etc
from
table
where
col_1 is null
is null checks if a column is null, nullif(#expr1,#expr2) could be rewritten as:
case when #expr1 = #expr2 return null else return #expr1 end
EDIT:
you can relax filters adding OR condition into the 'where' clause (TIP: remember AND is evaluated before OR)
select
col_1, col_2, etc
from
table
where
(col_1 is null OR col1 like 'production')
if you want to decide runtime wich one you neeed you could write a procedure:
create proc my_proc #var AS varchar(100) = 'NULL§159§' -- this defaults to null, if you put a parameter it queries with parameter passed
as
select
col_1, col_2, etc
from
table
where
WHERE coalesce(col_1,'NULL§159§') = #var
-- added §159§ symbol to the null to make sure the queried string is impossible in the database,
-- obviously into the database the value 'NULL159' hase become a sort of 'reserved word', but hopefully is odd enough not to appear in data
GO
and call it by exec my_proc('production')

Answer 2

Try this, it can handle the column with null values or empty space
SELECT
col_1, col_2, etc
FROM
Table
WHERE
ISNULL(NULLIF(col_1 ,''),'1') = '1'

Answer 3

You can do something like
select
col_1, col_2, etc
from
table
where
col_1 IS NULL OR col_1 = ''

Answer 4

select
col_1, col_2, etc
from
table
where
collaboration IS NULL OR collaboration ='Production'

Answer 5

Crystal ball time from me. This is my guess on what the OP wants:
DECLARE #Prod varchar(15);
--SET #Prod = 'Production';
SELECT {Columns}
FROM YourTable
WHERE Col1 = #Prod
OR (Col1 IS NULL AND #Prod IS NULL);

Answer 6

Try this.
DECLARE #SearchValue VARCHAR(50)
SELECT col_1, col_2, etc
FROM YourTable
WHERE ISNULL(col_1,'') = ISNULL(#SearchValue,'')