What is =1 doing here ?
SELECT TOP 3
NewsId,
NewsTitle,
NewsContent
FROM disc_News
WHERE CASE
WHEN DatePublish IS NOT NULL and DateExpired IS NOT NULL THEN 1
ELSE 0
END = 1
1 is just making the whole expression evaluate to true or false. Where clauses are supposed to evaluate Boolean expressions, otherwise you would have a syntax error
It is getting you the records where DatePublish AND DateExpired are NOT NULL.
The following WHERE clause should be equivalent
WHERE DatePublish IS NOT NULL
AND DateExpired IS NOT NULL
Related
I have an SQL query where the case expression is not working because I am getting the NULL value.
Any idea how to fix this?
select
td.reportEndDate,
CASE td.originalLinearAirDate
WHEN NULL THEN '12345678'
END As originalLinearAirDate
from
FROM DBA.Telecast td
where id = 2
order by
td.reportEndDate,
originalLinearAirDate;
You can use isnull
select
td.reportEndDate,
CASE WHEN td.originalLinearAirDate IS NULL THEN '19000101'
ELSE td.originalLinearAirDate
END As originalLinearAirDate
from
FROM DBA.Telecast td
where id = 2
order by
td.reportEndDate,
originalLinearAirDate;
You can use COALESCE() :
SELECT td.reportEndDate,
COALESCE(td.originalLinearAirDate, '12345678') AS originalLinearAirDate -- Use default date instead of '12345678'
FROM DBA.Telecast td
WHERE id = 2
ORDER BY td.reportEndDate, originalLinearAirDate;
In your case expression you didn't specified ELSE part hence you got NULL.
However, case expression will only return one type. So, you should check code or do necessary conversation.
The problem is the NULL comparison. The comparison is never true, even when used from comparison in a CASE expression.
If you wanted to do this using CASE, then you need to use IS NULL:
(CASE WHEN td.originalLinearAirDate IS NULL
THEN '12345678'
END) As originalLinearAirDate
If you want to return the original value in this case, you need an ELSE:
(CASE WHEN td.originalLinearAirDate IS NULL
THEN '12345678'
ELSE td.originalLinearAirDate
END) As originalLinearAirDate
Note that this will return an error if the column is really a DATE, because '12345678' cannot be converted to a date.
This version is better expressed using COALESCE():
COALESCE(td.originalLinearAirDate, '12345678')
When querying a boolean field that is null why does
Select * From MyTableName where [boolfieldX] <> 1
not return any rows with null in [boolfieldX]? 1 <> null I would have expected rows with null to be returned.
It is not possible to test for NULL values with comparison operators, such as =, <, or <>.
You have to use the IS NULL and IS NOT NULL operators instead, or you have to use functions like ISNULL() and COALESCE()
Select * From MyTableName where [boolfieldX] <> 1 OR [boolfieldX] IS NULL
OR
Select * From MyTableName where ISNULL([boolfieldX],0) <> 1
Read more about null comparison in Stackoverflow Documentation
Read more about ISNULL() and COALESCE() Functions in Stackoverflow Documentation
I believe that it's because null is an unknown value. You can't query against an unknown 'value'. In my opinion, referring to null as a 'value' is an oxymoron because it represents an unknown. Using the operators "Is Null" and "Not Is Null" in conjunction with whatever selection criteria will return the desired results, or translating it by converting a null an alternate value will work like this: IsNull([boolfield], 'some compatible value')
Hi try to use this query:
select * from mytablename where [boolFieldX] is null And [boolFieldX] <> 1
This is my first post, and I attempted to do a thorough search for this issue, so please accept my apologies if it has been posted elsewhere many times, but I'm wondering if anyone has encountered the following issue when attempting to remove NULLs from their result set:
case Occurrence
when NULL then '0'
else occurrence
end as Occurrence,
case Aggregate
when NULL then '0'
else Aggregate
end as Aggregate,
This didn't do anything to my NULLs; however, this did the trick:
case
when occurrence is NULL then '0'
else occurrence
end as Occurrence,
case
when aggregate is NULL then '0'
else Aggregate
end as Aggregate
Does anyone have any idea why this behaves this way? I'm using SQLServer2012.
I'm also not very versed in programming and only have less than a year SQL experience.
Thanks!
You should be using the ISNULL() or COALESCE() system function for handling nulls
something like
SELECT ISNULL(Occurrence , 0) AS Occurrence
,ISNULL(Aggregate , 0) AS Aggregate
FROM Table
OR
SELECT COALESCE(Occurrence , 0) AS Occurrence
,COALESCE(Aggregate , 0) AS Aggregate
FROM Table
The reason it didn't work in the case statement with
case Occurrence
when NULL then '0'
else occurrence
end as Occurrence,
is because it is interpreting it as
CASE
WHEN Occurrence = NULL THEN 0
ELSE Occurrence
END
Null is checked in sql server using IS NULL or IS NOT NULL if you use any other operator with null like = , <> or <, < it yields NULL hence the unexpected results.
Only for SQL Server 2012 and Later
In sql server 2012 and later versions you also have the IIF function
SELECT IIF(Occurrence IS NULL, 0, Occurrence) AS Occurrence
,IFF(Aggregate IS NULL , 0, Aggregate) AS Aggregate
FROM Table
You use simple case:
The simple CASE expression operates by comparing the first expression to the expression in each WHEN clause for equivalency. If these expressions are equivalent, the expression in the THEN clause will be returned.
Allows only an equality check.
case Occurrence
when NULL then '0'
else occurrence
end as Occurrence,
Which is executed as :
case
when occurence = NULL then '0'
else occurrence
end as Occurrence
Then expression occurence = NULL return NULL and is treated like False
Second your case use searched CASE with full condition and works fine:
case
when occurrence IS NULL then '0'
else occurrence
end as Occurrence,
So your question is about difference column IS NULL vs column = NULL
try
select 1 where null =null
select 1 where null is null
your statement looks like null equals null
select case when null is null then 1 else 0 end
select case null when null then 1 else 0 end
In your case use ISNULL this will give you the results your after
SELECT ISNULL(null,1)
I have a table with a column of image type, the table has some rows but all the rows haven't had any image yet, they are all null. To test the CASE WHEN NULL, I've tried this and it gave a strange result:
SELECT CASE myImageColumn WHEN NULL THEN 0 ELSE 1 END FROM myTable
All the returned rows were in a column of 1's (I thought 0's). What is wrong here?
Your help would be highly appreciated!
Thank you!
You can't compare with NULL like that, you should try:
SELECT CASE WHEN myImageColumn IS NULL THEN 0 ELSE 1 END
FROM myTable
Use a different form of CASE instead:
SELECT CASE WHEN myImageColumn IS NULL THEN 0 ELSE 1 END FROM myTable
Two useful links:
http://www.sqlite.org/nulls.html
http://www.sqlite.org/lang_expr.html
There's a bypass:
CASE ifnull(myValue, 'someUniqueStringOrValue')
WHEN 'someUniqueStringOrValue' THEN 0 -- this means null
WHEN 'someNormalValue' THEN 1
END
select 'true' from dual where 1 not in (null,1);
when we execute this which will result nothing
what my question is:
is the above query is logically equivalent to
select 'true' from dual where 1 != null and 1 != 1;
which will result nothing just as above statement
Please clarify?
Correct (but note that IN is an operator, not a clause and it works like this in SQL in general, not only for Oracle).
where 1 not in (null,1)
is equivalent to:
where 1 != null and 1 != 1
which should really be written as:
WHERE 1 NOT IN (NULL, 1)
and
WHERE 1 <> NULL AND 1 <> 1
which is the same as:
WHERE (1 <> NULL) AND (1 <> 1)
which evaluates to:
WHERE UNKNOWN AND FALSE
and further as:
WHERE FALSE
So, it correctly returns no rows.
Notice that if you had WHERE 1 NOT IN (NULL, 2), it would evaluate to WHERE UNKNOWN (left as an exercise) and no rows would be returned either.
The issue of your script in comparing with NULL value. You should use
column is null and column = 1
Actually NULL is an undefined value. Any comparation with NULL gives neither True nor False but NULL. Even NULL = NULL
That's why your 1 not in (null,1) doesn't work.
Yes they are.
select something from table where column not in (1,2,3);
is equivalent to
select something from table where column != 1 and column != 2 and column != 3;
The IN statement is a collection of OR statements, while NOT IN is a collection of AND statements - but it is also not equal to.
So the NOT IN is equivalent to:
1 <> NULL
AND 1 <> 1
AND ...
While the IN would be equivalent to:
1 = NULL
OR 1 = 1
OR ...
Note that having NULL in the collection will not work, due to the quirky nature of NULL.
Yes. It is correct. Also NULL values should be compared with IS NULL