Since I have a table with milions of records, I've been looking for a solution to update data in one column more efficiently, without using UNDO tablespace and UPDATE statement.
My idea was to create a second table (copy) X from the target table Y, as follows:
create table X as
select col1,col2,col3, (case when col4 is not null and createdate < sysdate - 180 then null else col4) as col4 from Y;
Then drop table Y and rename X to Y. It creates the table but my test query
select count(col4) from Y where col4 is not null and createdate < sysdate - 180
Shows that there are still some records with original value (looks like case clause does not work as suppose to). When I use the same select in subquery and the exact same condition, like
select count(col4) from (select col1,col2,col3, (case when col4 is not null and createdate < sysdate - 180 then null else col4) as col4 from Y) where col4 is not null and createdate < sysdate - 180
The result is 0. Am I doing something incorrectly?
Well I think I have figured that out:
The problem here is sysdate as I tried to at first clone the table (sysdate1) and then validate the data using sysdate in where conditions (sysdate2 different from the first one)
Subquery print 0 as it takes the same sysdate for both conditions.
I was trying to filter out some predefined values from a table sample which has two column col1 and col2.
My query:
select *
from sample
where (col1 is not null or col2 is not null)
and col1 not in (1,2)
and col2 not in (3,4);
However, the above query filter out all the null values (in col1 or col2 ).
Example: the below row is filtered out,
col1 col2
---------
7 null
null 8
I get the expected result when i modify the query to below.
select *
from sample
where (col1 is not null or col2 is not null)
and (col1 not in (1,2) or col1 is null)
and (col2 not in (3,4) or col2 is null);
Why NOT IN filters out rows with NULL value even though I am not specified NULL in NOT IN ?
Nothing is equal to NULL, and is anything not equal to NULL. For an expression like NULL NOT IN (1,2), this evaluates to unknown which (importantly) is not true; meaning that the WHERE is not met. This is why your second query, where you handle your NULLs works.
Alternatively, you could use an EXISTS. It's perhaps not an intuitive, but handles NULL values:
WITH VTE AS(
SELECT *
FROM (VALUES(1,3),(2,4),(3,5),(7,NULL),(NULL,8))V(col1,col2))
SELECT *
FROM VTE
WHERE NOT EXISTS(SELECT 1
WHERE Col1 IN (1,2)
AND Col2 IN (3,4));
Try this
SET ANSI_NULLS OFF
select *
from sample
where (col1 is not null or col2 is not null)
and col1 not in (1,2)
and col2 not in (3,4);
ANSI NULL ON/OFF:
This option specifies the setting for ANSI NULL comparisons. When this is on, any query that compares a value with a null returns a 0. When off, any query that compares a value with a null returns a null value (https://blog.sqlauthority.com/2007/03/05/sql-server-quoted_identifier-onoff-and-ansi_null-onoff-explanation/#:~:text=ANSI%20NULL%20ON%2FOFF%3A,null%20returns%20a%20null%20value.).
this discussed in https://stackoverflow.com/questions/129077/null-values-inside-not-in-clause#:~:text=NOT%20IN%20returns%200%20records,not%20the%20value%20being%20tested.
This issue came up when I got different records counts for what I thought were identical queries one using a not in where constraint and the other a left join. The table in the not in constraint had one null value (bad data) which caused that query to return a count of 0 records. I sort of understand why but I could use some help fully grasping the concept.
To state it simply, why does query A return a result but B doesn't?
A: select 'true' where 3 in (1, 2, 3, null)
B: select 'true' where 3 not in (1, 2, null)
This was on SQL Server 2005. I also found that calling set ansi_nulls off causes B to return a result.
Query A is the same as:
select 'true' where 3 = 1 or 3 = 2 or 3 = 3 or 3 = null
Since 3 = 3 is true, you get a result.
Query B is the same as:
select 'true' where 3 <> 1 and 3 <> 2 and 3 <> null
When ansi_nulls is on, 3 <> null is UNKNOWN, so the predicate evaluates to UNKNOWN, and you don't get any rows.
When ansi_nulls is off, 3 <> null is true, so the predicate evaluates to true, and you get a row.
NOT IN returns 0 records when compared against an unknown value
Since NULL is an unknown, a NOT IN query containing a NULL or NULLs in the list of possible values will always return 0 records since there is no way to be sure that the NULL value is not the value being tested.
Whenever you use NULL you are really dealing with a Three-Valued logic.
Your first query returns results as the WHERE clause evaluates to:
3 = 1 or 3 = 2 or 3 = 3 or 3 = null
which is:
FALSE or FALSE or TRUE or UNKNOWN
which evaluates to
TRUE
The second one:
3 <> 1 and 3 <> 2 and 3 <> null
which evaluates to:
TRUE and TRUE and UNKNOWN
which evaluates to:
UNKNOWN
The UNKNOWN is not the same as FALSE
you can easily test it by calling:
select 'true' where 3 <> null
select 'true' where not (3 <> null)
Both queries will give you no results
If the UNKNOWN was the same as FALSE then assuming that the first query would give you FALSE the second would have to evaluate to TRUE as it would have been the same as NOT(FALSE).
That is not the case.
There is a very good article on this subject on SqlServerCentral.
The whole issue of NULLs and Three-Valued Logic can be a bit confusing at first but it is essential to understand in order to write correct queries in TSQL
Another article I would recommend is SQL Aggregate Functions and NULL.
Compare to null is undefined, unless you use IS NULL.
So, when comparing 3 to NULL (query A), it returns undefined.
I.e. SELECT 'true' where 3 in (1,2,null)
and
SELECT 'true' where 3 not in (1,2,null)
will produce the same result, as NOT (UNDEFINED) is still undefined, but not TRUE
IF you want to filter with NOT IN for a subquery containg NULLs justcheck for not null
SELECT blah FROM t WHERE blah NOT IN
(SELECT someotherBlah FROM t2 WHERE someotherBlah IS NOT NULL )
The title of this question at the time of writing is
SQL NOT IN constraint and NULL values
From the text of the question it appears that the problem was occurring in a SQL DML SELECT query, rather than a SQL DDL CONSTRAINT.
However, especially given the wording of the title, I want to point out that some statements made here are potentially misleading statements, those along the lines of (paraphrasing)
When the predicate evaluates to UNKNOWN you don't get any rows.
Although this is the case for SQL DML, when considering constraints the effect is different.
Consider this very simple table with two constraints taken directly from the predicates in the question (and addressed in an excellent answer by #Brannon):
DECLARE #T TABLE
(
true CHAR(4) DEFAULT 'true' NOT NULL,
CHECK ( 3 IN (1, 2, 3, NULL )),
CHECK ( 3 NOT IN (1, 2, NULL ))
);
INSERT INTO #T VALUES ('true');
SELECT COUNT(*) AS tally FROM #T;
As per #Brannon's answer, the first constraint (using IN) evaluates to TRUE and the second constraint (using NOT IN) evaluates to UNKNOWN. However, the insert succeeds! Therefore, in this case it is not strictly correct to say, "you don't get any rows" because we have indeed got a row inserted as a result.
The above effect is indeed the correct one as regards the SQL-92 Standard. Compare and contrast the following section from the SQL-92 spec
7.6 where clause
The result of the is a table of those rows of T for
which the result of the search condition is true.
4.10 Integrity constraints
A table check constraint is satisfied if and only if the specified
search condition is not false for any row of a table.
In other words:
In SQL DML, rows are removed from the result when the WHERE evaluates to UNKNOWN because it does not satisfy the condition "is true".
In SQL DDL (i.e. constraints), rows are not removed from the result when they evaluate to UNKNOWN because it does satisfy the condition "is not false".
Although the effects in SQL DML and SQL DDL respectively may seem contradictory, there is practical reason for giving UNKNOWN results the 'benefit of the doubt' by allowing them to satisfy a constraint (more correctly, allowing them to not fail to satisfy a constraint): without this behaviour, every constraints would have to explicitly handle nulls and that would be very unsatisfactory from a language design perspective (not to mention, a right pain for coders!)
p.s. if you are finding it as challenging to follow such logic as "unknown does not fail to satisfy a constraint" as I am to write it, then consider you can dispense with all this simply by avoiding nullable columns in SQL DDL and anything in SQL DML that produces nulls (e.g. outer joins)!
In A, 3 is tested for equality against each member of the set, yielding (FALSE, FALSE, TRUE, UNKNOWN). Since one of the elements is TRUE, the condition is TRUE. (It's also possible that some short-circuiting takes place here, so it actually stops as soon as it hits the first TRUE and never evaluates 3=NULL.)
In B, I think it is evaluating the condition as NOT (3 in (1,2,null)). Testing 3 for equality against the set yields (FALSE, FALSE, UNKNOWN), which is aggregated to UNKNOWN. NOT ( UNKNOWN ) yields UNKNOWN. So overall the truth of the condition is unknown, which at the end is essentially treated as FALSE.
SQL uses three-valued logic for truth values. The IN query produces the expected result:
SELECT * FROM (VALUES (1), (2)) AS tbl(col) WHERE col IN (NULL, 1)
-- returns first row
But adding a NOT does not invert the results:
SELECT * FROM (VALUES (1), (2)) AS tbl(col) WHERE NOT col IN (NULL, 1)
-- returns zero rows
This is because the above query is equivalent of the following:
SELECT * FROM (VALUES (1), (2)) AS tbl(col) WHERE NOT (col = NULL OR col = 1)
Here is how the where clause is evaluated:
| col | col = NULL⁽¹⁾ | col = 1 | col = NULL OR col = 1 | NOT (col = NULL OR col = 1) |
|-----|----------------|---------|-----------------------|-----------------------------|
| 1 | UNKNOWN | TRUE | TRUE | FALSE |
| 2 | UNKNOWN | FALSE | UNKNOWN⁽²⁾ | UNKNOWN⁽³⁾ |
Notice that:
The comparison involving NULL yields UNKNOWN
The OR expression where none of the operands are TRUE and at least one operand is UNKNOWN yields UNKNOWN (ref)
The NOT of UNKNOWN yields UNKNOWN (ref)
You can extend the above example to more than two values (e.g. NULL, 1 and 2) but the result will be same: if one of the values is NULL then no row will match.
Null signifies and absence of data, that is it is unknown, not a data value of nothing. It's very easy for people from a programming background to confuse this because in C type languages when using pointers null is indeed nothing.
Hence in the first case 3 is indeed in the set of (1,2,3,null) so true is returned
In the second however you can reduce it to
select 'true' where 3 not in (null)
So nothing is returned because the parser knows nothing about the set to which you are comparing it - it's not an empty set but an unknown set. Using (1, 2, null) doesn't help because the (1,2) set is obviously false, but then you're and'ing that against unknown, which is unknown.
It may be concluded from answers here that NOT IN (subquery) doesn't handle nulls correctly and should be avoided in favour of NOT EXISTS. However, such a conclusion may be premature. In the following scenario, credited to Chris Date (Database Programming and Design, Vol 2 No 9, September 1989), it is NOT IN that handles nulls correctly and returns the correct result, rather than NOT EXISTS.
Consider a table sp to represent suppliers (sno) who are known to supply parts (pno) in quantity (qty). The table currently holds the following values:
VALUES ('S1', 'P1', NULL),
('S2', 'P1', 200),
('S3', 'P1', 1000)
Note that quantity is nullable i.e. to be able to record the fact a supplier is known to supply parts even if it is not known in what quantity.
The task is to find the suppliers who are known supply part number 'P1' but not in quantities of 1000.
The following uses NOT IN to correctly identify supplier 'S2' only:
WITH sp AS
( SELECT *
FROM ( VALUES ( 'S1', 'P1', NULL ),
( 'S2', 'P1', 200 ),
( 'S3', 'P1', 1000 ) )
AS T ( sno, pno, qty )
)
SELECT DISTINCT spx.sno
FROM sp spx
WHERE spx.pno = 'P1'
AND 1000 NOT IN (
SELECT spy.qty
FROM sp spy
WHERE spy.sno = spx.sno
AND spy.pno = 'P1'
);
However, the below query uses the same general structure but with NOT EXISTS but incorrectly includes supplier 'S1' in the result (i.e. for which the quantity is null):
WITH sp AS
( SELECT *
FROM ( VALUES ( 'S1', 'P1', NULL ),
( 'S2', 'P1', 200 ),
( 'S3', 'P1', 1000 ) )
AS T ( sno, pno, qty )
)
SELECT DISTINCT spx.sno
FROM sp spx
WHERE spx.pno = 'P1'
AND NOT EXISTS (
SELECT *
FROM sp spy
WHERE spy.sno = spx.sno
AND spy.pno = 'P1'
AND spy.qty = 1000
);
So NOT EXISTS is not the silver bullet it may have appeared!
Of course, source of the problem is the presence of nulls, therefore the 'real' solution is to eliminate those nulls.
This can be achieved (among other possible designs) using two tables:
sp suppliers known to supply parts
spq suppliers known to supply parts in known quantities
noting there should probably be a foreign key constraint where spq references sp.
The result can then be obtained using the 'minus' relational operator (being the EXCEPT keyword in Standard SQL) e.g.
WITH sp AS
( SELECT *
FROM ( VALUES ( 'S1', 'P1' ),
( 'S2', 'P1' ),
( 'S3', 'P1' ) )
AS T ( sno, pno )
),
spq AS
( SELECT *
FROM ( VALUES ( 'S2', 'P1', 200 ),
( 'S3', 'P1', 1000 ) )
AS T ( sno, pno, qty )
)
SELECT sno
FROM spq
WHERE pno = 'P1'
EXCEPT
SELECT sno
FROM spq
WHERE pno = 'P1'
AND qty = 1000;
this is for Boy:
select party_code
from abc as a
where party_code not in (select party_code
from xyz
where party_code = a.party_code);
this works regardless of ansi settings
also this might be of use to know the logical difference between join, exists and in
http://weblogs.sqlteam.com/mladenp/archive/2007/05/18/60210.aspx
I am having an issue with a query only in one particular environment/database even if the data is almost similar. Here is the simplified scenario:
Table A - One column - Id (long)
Id
1
2
3
Table B - Two columns - value(varchar) and field2(varchar)
Value Field2
1)abc NotKey
2)Test NotKey
3)1 Key
4)1.56 NotKey
When I run the query
select * from table a
where id in(select value from table b where Field2 = 'Key')
I get the error
Result: Conversion failed when converting the varchar value 'abc' (earlier I had this value erraneously as 'NotKey') to data type int.
on one database. In three other databases, the value returns correctly as "1".
I am using SQL Server 2008. What might be the issue here?
You gave the wrong filter for the filter that leads to the error.
The errror only happens when you select:
select * from tablea
where id in(select value from tableb where Field2 = 'NotKey')
You have to cast one of the columns
select * from tablea
where cast( id as nvarchar(20)) in(select value from tableb where Field2 = 'NotKey')
http://sqlfiddle.com/#!6/e9223/23
You must have a record in this instance that doesn't follow the same pattern as before. Try running the following query to find your bad data. You could either fix the record or add a numeric check to the query you're using.
select *
from table
where Field2 = 'Key'
and (ISNUMERIC(Value) = 0
OR CHARINDEX('.', Value) > 0);
Filtered query:
select *
from table a
where id in
(
select value
from table b
where Field2 = 'Key'
and ISNUMERIC(value) = 1
and CHARINDEX('.', Value) = 0
);
I am working in SQL Server 2008. I have 2 queries. The first one is:
SELECT
col1,
col2
FROM tableA
A typical result set of this query is:
col1 col2
facilityA 10
facilityB 20
The second one is:
SELECT
colx,
COUNT(*) AS 'Totals'
FROM tableB
GROUP BY colx
A typical result set of this query is:
colx Totals
facilityA 10
facilityB 50
I want to return all records in the first result set where the values are different between col2 and Totals from the second result set, for corresponding values between col1 and colx. For instance, the given example should return:
col1 col2
facilityB 20
How do I achieve this?
Sounds like you want to use the EXCEPT clause. This will compare each row column by column and if an identical row exists between the two datasets it will be excluded:
SELECT col1, col2
FROM tableA
EXCEPT
SELECT colx, COUNT(*) AS 'Totals'
FROM tableB
GROUP BY colx