Case Statement in Where Clause NULL case [duplicate] - sql

Question

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CASE in WHERE, SQL Server
(5 answers)
Closed 4 years ago.
I'm creating a query (to eventually be used in a stored procedure) with multiple variations on what criteria is entered in a form. Sometimes there can be an entry, sometimes not. Sometimes the data field has a value, sometimes it's NULL.
The fields in my form are NAME, SSN, and DRLICENSE.
DECLARE #name VARCHAR(30);
DECLARE #ssn VARCHAR(10);
DECLARE #drlic VARCHAR(10);
--(if for example, someone enters data in two of the fields like this...)
SET #name = 'SMITH'
SET #drlic = 'D'
(In stored procedure)
SET #name = #name + '%'
SET #ssn = #ssn + '%'
SET #drlic = #drlic + '%'
SELECT
NAME,
SSN,
DRLICENSE
FROM
TABLE
WHERE
NAME LIKE CASE WHEN LEN(#name) > 1 THEN #name ELSE NAME END
AND SSN LIKE CASE WHEN len(#ssn) > 1 THEN #ssn ELSE SSN END
AND DRLICENSE LIKE CASE WHEN LEN(#drlic) > 1 THEN #drlic ELSE DRLICENSE END
The idea behind my case statement is to check the variable for usage and perform a like if the name, ssn, or drlicense are partial entries.
My question is: how do I account for the case of NULL in the table column (i.e. SSN LIKE SSN does not work when SSN is NULL because SSN IS NULL needs to be there).

Answer 1

This isn't going to perform well, especially since you are using LIKE but parentheses are important here
where ((#name is null or name like '%' + #name + '%') or ( name is null))
and ((#ssn is null or ssn like '%' + #ssn + '%') or (ssn is null))
and ((#drlic is null or DRLICENSE like '%' + #drlic + '%') or (DRLICENSE is null))
This will return the NULL values in those columns regardless if a parameter is passed in or not. If you don't want the NULL then just remove the or ( name is null)) section from each line. I wasn't certain from your post.

Answer 2

if length(#foo) <= 1
set #foo = NULL
if length(#bar) <= 1
set #bar = NULL
...
WHERE (#foo is NULL or t.foo = #foo)
AND (#bar is NULL or t.bar like #bar)
OPTION (RECOMPILE)

Answer 3

This should do it:
WHERE (#name IS NULL OR name LIKE #name + '%')
AND (#ssn IS NULL OR ssn LIKE #ssn + '%')
AND (#drlic IS NULL OR drlicense LIKE #drlic + '%')
Note that if, for example, user searched for name = foo then it will return rows that match foo% and not rows that have NULL name.

Answer 4

You can inline adding the wild card to the parameter value and add your null checks inline as well. There is no need for a CASE statement either. For each of the parameter/column values the result returns true if the parameter is null or if the column value is null or if the column value starts with the passed in parameter value.
Where statement:
WHERE (Name IS NULL OR #name IS NULL OR Name LIKE #name + '%')
AND (SSN IS NULL OR #ssn IS NULL OR SSN LIKE #ssn + '%')
AND (DRLICENSE IS NULL OR #drlic IS NULL OR DRLICENSE LIKE #drlic + '%')
The key here is to not do any filtering if the incoming value to use is null or if the column value is null which I assume you do not want filtered on if it is null.

Answer 5

You could use ISNULL() it's very useful in cases like yours.
SELECT
NAME,
SSN,
DRLICENSE
FROM
TABLE
WHERE
ISNULL(NAME,0) LIKE ISNULL(ISNULL(#name, NAME),0)
AND ISNULL(SSN,0) LIKE ISNULL(ISNULL(#ssn, SSN),0)
AND ISNULL(DRLICENSE,0) LIKE ISNULL(ISNULL(#drlic, DRLICENSE),0)
This method will replace the NULL values with the column value if the column value is NULL then both will be set to 0 (which will be 0=0, which will always be true).

Answer 6

If I understand correctly, you want a NULL-safe equality. That is, you want NULL to match NULL and values to match values. So:
where (name = #name or (name is null and #name is null)) and
(ssn = #ssn or (ssn is null and #ssn is null)) and
(drlicense = #drlicense or (drlicense is null and #drlicense is null))
or, an intriguing variant:
where (select count(*)
from (select distinct *
from (values (name, 'name'), (#name, 'name'), (ssn, 'ssn'), (#ssn, 'ssn'), (drlicense, 'drlicense'), (#drlicense, 'drlicense')
v(val, which)
) x
) = 3
This is using group by semantics to combine NULL values.
Or, if you want some obfuscation:
where nullif(name, #name) is null and nullif(#name, name) is null and
nullif(ssn, #ssn) is null and nullif(#ssn, ssn) is null and
nullif(drlicense, #drlicense) is null and nullif(#drlicense, drlicense) is null