I have an SQL server database that I am querying and I only want to get the information when a specific row is null. I used a where statement such as:
WHERE database.foobar = NULL
and it does not return anything. However, I know that there is at least one result because I created an instance in the database where 'foobar' is equal to null. If I take out the where statement it shows data so I know it is not the rest of the query.
Can anyone help me out?
Correct syntax is WHERE database.foobar IS NULL. See http://msdn.microsoft.com/en-us/library/ms188795.aspx for more info
Comparison to NULL will be false every time. You want to use IS NULL instead.
x = NULL -- always false
x <> NULL -- always false
x IS NULL -- these do what you want
x IS NOT NULL
Read Testing for Null Values, you need IS NULL not = NULL
Is it an SQL Server database?
If so, use IS NULL instead of making the comparison (MSDN).
Related
Is there a way in sql to, by default bring back values regardless of if they are true or false?
for example I have a column, 'Mandatory' which datatype is a bit.
Is there a way to bring back records where the column 'Mandatory' is either true or false or null?
something like
Select * From Table Where Mandatory = .... etc
select * from Table
where mandatory is null or mandatory in (0,1)
If the mandatory is a bit, this code is definitely true. There is no other possibility.
Let me assume you are using SQL Server -- because it supports bit but not boolean.
You can use:
where mandatory = 1
or
where mandatory = 'true'
resolved by doing this
ISNULL(Mandatory,0) =
CASE
WHEN #Mandatory = 0 THEN 0
WHEN #Mandatory = 1 THEN 1
WHEN #Mandatory = 2 THEN ISNULL(Mandatory,0)
essentially saying that when 2 is inputted, it will bring back all values for true, false and null. works very well
The question is how to run a binary logic into trinary logic.
Binary = There are distinct, actual values: in regards to this question the values [True] or [False]
Trinary = There are distinct, actual values plus unknown values: in regards to this question the values [ True | False | NULL ]
It is not possible to include unknown values in a single WHERE condition. Instead it has to be checked separately:
WHERE mandatory IN (0, 1) -- check whether TRUE or FALSE against bit
OR mandatory IS NULL -- also include UNKNOWN
This approach is better than using a function as a function in a WHERE condition can (and will) lead more often than not to performance losses.
I'm trying to add to current query where a certain field name must contain either 'Y' or 'N'. I'm currently using substrings and isnumeric functions to manipulate the data within.
Here is an example:
(
LEN(STERLING_RETURN_SIGNAL) > 1
or ISNUMERIC(substring(STERLING_RETURN_SIGNAL,1,1)) = 1
)
So the STERLING_RETURN_SIGNAL, must either be 'Y' or 'N' otherwise +('Error message').
Many thanks. Using Sql Server Management Studio.
Please note, I am a beginner...
select
case
when
STERLING_RETURN_SIGNAL in ('Y','y','N','n')
then STERLING_RETURN_SIGNAL
else
'Invalid value for signal'
end as signal
from ...
I have written a Stored procedure in which in given table column named xx can have 0,1 or null. When I give the below condition. SP is ignoring null and returning data only for 0 value.
WHERE (CAR_INSPECTION_NEW_TEST.NODAMAGEFLAG is null OR
CAR_INSPECTION_NEW_TEST.NODAMAGEFLAG = 0) AND
CAR_INSPECTION_NEW_TEST.ISSUBJECT_TODELIVER = 0
Can any one tell what is the problem?
By simple logic it will not return rows where NODAMAGEFLAG is null as long as ISSUBJECT_TODELIVER = 0 is not also valid (because of the AND).
So, check your data please.
In NAME table FIRST column is having null but no rows are selected. Please help me to understand.
SELECT * FROM NAME WHERE FIRST != '1'
Any comparison with null is false - = and <>, >, <, and so on. You cannot use null in an IN list as well - it would be ignored. Moreover, two nulls are not even equal to each other.
To get the nulls, you need to ask for them explicitly, like this:
SELECT * FROM NAME WHERE FIRST IS NULL OR FIRST != '1'
Any comparison to NULL returns NULL, which is equivalent to FALSE. This is true eve of not-equals.
If you want to include NULL values, do one of the following:
where first <> '1' or first is null
or
where coalesce(first, '<null>') <> '1'
In Oracle, null is not considered a legal value to select unless you explicitly ask for it:
select * from name where (first != '1') or first is null
You could also use NVL (similar to coalesce):
select * from name where nvl(first,'0') != '1'
That is correct because NULL can never be compared with anything else....
The only option that you have is to include a NULL check as an or in the command
SELECT * FROM NAME WHERE FIRST!=1 OR FIRST IS NULL
According to Oracle Documentation NULL is defined as a value not knownm or when the value is not meaningful. That is solely the reason why Oracle mentions not consider a value of ZERO as NULL. This is just an FYI, an addon. Thanks!
NULL is dumb. Period.
NULL is evil.
If X is NULL and Y is NULL, then X does in fact equal Y because they are both NULL.
It's also a PITA that I can't say
IF X IN ('a','B','C', null)
Because this condition happens. But now I have to say
IF ( X IN ('a','B','C') or X is NULL )
which is a waste of time and a risk of error if I forget the parentheses.
What irks me further is that NULL shouldn't happen in the first place. Fields (er... ok kids, I'll call them Columns) should always be initialized. Period. Stop the nulls. Don't allow them. Default values should always be zeroes or blanks so that those folks that are too lazy to initialize columns in their software will have them initialized for them automatically.
There are many instances where a failure to define default values of zeroes and blanks makes life more difficult than it has to be.
I'm attempting to create a T-SQL case statement to filter a query based on whether a field is NULL or if it contains a value. It would be simple if you could assign NULL or NOT NULL as the result of a case but that doesn't appear possible.
Here's the psuedocode:
WHERE DateColumn = CASE #BitInput
WHEN 0 THEN (all null dates)
WHEN 1 THEN (any non-null date)
WHEN NULL THEN (return all rows)
From my understanding, the WHEN 0 condition can be achieved by not providing a WHEN condition at all (to return a NULL value).
The WHEN 1 condition seems like it could use a wildcard character but I'm getting an error regarding type conversion. Assigning the column to itself fixes this.
I have no idea what to do for the WHEN NULL condition. My internal logic seems to think assigning the column to itself should solve this but it does not as stated above.
I have recreated this using dynamic SQL but for various reasons I'd prefer to have it created in the native code.
I'd appreciate any input. Thanks.
The CASE expression (as OMG Ponies said) is mixing and matching datatypes (as you spotted), in addition you can not compare to NULL using = or WHEN.
WHERE
(#BitInput = 0 AND DateColumn IS NULL)
OR
(#BitInput = 1 AND DateColumn IS NOT NULL)
OR
#BitInput IS NULL
You could probably write it using CASE but what you want is an OR really.
You can also use IF..ELSE or UNION ALL to separate the 3 cases