Note: This contest is over, so enjoy the brain teaser about ANSI_NULL. We all love puzzles and here is interesting puzzle which you can play with me and win Amazon Gift Cards and Bubble Copter R/C. The contest for Amazon Gift Card is open worldwide, however, Bubble Copter winner will be chosen from USA only.
First run following script:
SET ANSI_NULLS ON;
-- Query1
SELECT 'SQLAuthority' AS Statement11
WHERE 'Authority' IN ('S','Q', 'L', 'Authority', NULL);
-- Query 2
SELECT 'SQLAuthority' AS Statement12
WHERE 'Authority' NOT IN ('S','Q', 'L', NULL);
You will get the following result:
You can clearly see that in the first case we are getting different results. Here are the questions you need to answer to win the Amazon Gift Cards and Bubble Copter R/C.
There are two steps to take participate in the contest:
Step 1: Answer the Question
Question: Why do Query 1 return results but Query 2 does not return any result?
Answer this question in comments area along with the question in Step2.
Giveaway:
- 2 lucky winners will get USD 25 worth Amazon Gift Card (Open worldwide, Total giveaway value USD 50)
- One lucky winner from USA will get Bubble Copter R/C (Shipping from USA to other countries is not possible)
Rules and Conditions:
- Contest open till May 25, 2013 12:00 GMT.
- Please leave your answer in the comment area in following format:
- Answer to Q1:
- Please note that winner will be selected after May 25th by random selection and will be posted as a comment to this blog.
- The answers will be kept hidden till the winner will be announced to have fair competition.
Reference: Pinal Dave (https://blog.sqlauthority.com)
115 Comments. Leave new
since not in is a logical operator
Logical Operators
Logical operators test for the truth of some condition. Logical operators, like comparison operators, return a Boolean data type with a value of TRUE or FALSE.
When
SET ANSI_NULLS ONit means ISO Standard is being followed.
means
= and should not be used for null comparison.
If you want to use = or for null comparison use
SET ANSI_NULLS OFFit means do not follow ISO Standard.
SET ANSI_NULLSshould be set to ON for executing distributed queries
for maintaining compatibility of queries accross Servers.
Question 2) i am not authorized to download from office , i shall do it from home
Answer to Q1:
As SET ANSI_NULLS ON;
is TOP statement.
So, when Authority is compared to NULL as follows..
i.e Authority NULL evaluates to false always…This created problem. So no result come to you.
‘Authority’ ‘S’ – False
‘Authority’ ‘Q’ – False
‘Authority’ ‘L’ – False
‘Authority’ NULL – False
As SET ANSI_NULLS OFF will fetch result for second statement.
SELECT ‘SQLAuthority’ AS Statement11
WHERE ‘Authority’ IN (‘S’,’Q’, ‘L’, ‘Authority’, NULL);
This give result because ‘Authority= ‘Authority’ which evaluates to true among
‘Authority’ = ‘S’ – False
‘Authority’ = ‘Q’ – False
‘Authority’ = ‘L’ – False
‘Authority’ = ‘Authority – True
‘Authority’ = NULL – False
Answer to Q2:
11683.84 KB
Answer to Q1 : SET ANSI_NULLS OFF is missing
Answer to Q2 : 11683.8 KB
Answer to Q1:
‘Authority’ is there the list given list (‘S’,’Q’, ‘L’, ‘Authority’, NULL);
Answer to Q2
SQL server considers null as unknown.
Answer to Q1:
The NULL value affects the outcome of the NOT IN operator. This is because the operator compares each Value in the list; like ‘Authority’ ‘S’ and ‘Authority’ ‘Q’ and ‘Authority’ ‘L’ and ‘Authority’ NULL
We know Null is an unknown value so ‘Authority’ NULL condition fails then there no record return. Mean time IN works fine because NULL NULL so the first statement returns value.
Answer to Q2: 11,686.1083984375 KB
Hi Pinaldave
I think the answer is in your another article in this blog with heading “SQL SERVER – QUOTED_IDENTIFIER ON/OFF and ANSI_NULL ON/OFF Explanation”. in this you clearly mentioned the explation like “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.”
Query 1 is same as:
select ‘SQLAuthority’ as statement1
where ‘Authority’ = ‘S’ or ‘Authority’=’Q’ or ‘Authority’ =’L’ or ‘Authority’=’Authority’ or ‘Authority’=NULL
WHICH IS FALSE or FALSE or FALSE or TRUE or UNKNOWN respectively
WHICH evaluates to true and we get the result
Query 2 is same as:
select ‘SQLAuthority’ as statement1
where ‘Authority’ ‘S’ and ‘Authority’ ‘Q’ and ‘Authority’ ‘L’ and ‘Authority’ Null
WHICH IS TRUE and TRUE and TRUE and UNKNOWN respectively
which evaluates to UNKNOWN.
So
1.)when ansi_nulls is ON, ‘Authority’ NULL is UNKNOWN, so the predicate evaluates to UNKNOWN and we dont get any result.
2.)when ansi_nulls is OFF,’Authority’ NULL is TRUE, so the predicate evaluates to TRUE and we get the results.
Answer to Q1: when you set ansi_nulls_on, management studio cannot compare null value to result true or false. it results to unknown. when we set ansi null off. it begins to compare null value to true or false.
Answer to Q1: In ANSI_NULL, any condition compared to NULL returns false.
Fundamental difference between IN and NOT IN is combination of conditions with OR and AND respectively. One of the condition has to be true in IN clause while all conditions have to be true in NOT IN clause to be able to return results. Since comparison condition with NULL in first query is false but comparison condition with “Authority” is true, it will return result set, while in the second query it won’t return resultset.
Answer to Q2: 11687 KB is the size of the file.
Step:1
query1 returned result because it satisfied the where condition ‘Authority’=’Authority’
while the query2 doesn’t, there is no match for ‘Authority’ in second query.
Step:2
Size of DevArt Schema Compare installation file in KB is as
12185.6KB
Answer to Q1:It is because the ANSI_NULLS is ON and NOT IN operator does not work with Null values. the null value affects the outcome of the NOT IN operator.
Query 1 is the same as:
select ‘true’ where ‘Authority’ = ‘S’ or ‘Authority’ = ‘Q’ or ‘Authority’ =’L’ or ‘Authority’ =’Authority’ or ‘Authority’=null
since ‘Authority’ =’Authority’ and you get a result.
Query 2 is the same as:
select ‘true’ where ‘Authority’ S and ‘Authority’ Q and ‘Authority’ L and ‘Authority’ null
When ansi_nulls is on, ‘Authority’ null is UNKNOWN, so the predicate evaluates to UNKNOWN, and you don’t get any rows.
When ansi_nulls is off, ‘Authority’ null is true, so the predicate evaluates to true, and you get a row.
Answer to Q2:11683.84 KB
Answer to Q1: Due to Setting ANSI_NULLS ON Both queries performing different. When ANSI_NULLS is on it consider NULL as unknown and ignore result containing NULL values and when ANSI_NULLS set to OFF it consider NULL values.
Answer to Q2:
File Size is :- 11, 686.11 KB
Answer to Q1:
The Query1 return results because the WHERE clause matches the literal value with one of the list value included with IN predicate.
If, the value to be compared was not exists in the list of IN predicate then it would be sure no results will appear, this is because comparision with NULL value evaluates to UNKNOWN due to SET ANSI_NULLS ON statement.
The Query2 does not return results because of ANSI_NULLS is set to ON. This is because the comparision against NULL value evaluates to UNKNOWN.
This is an ISO compliant behavior of comparision operators when they are used with null values.
Answer to Q2:
The size of the DevArt Schema Compare Installation file is 11,687 KB.
Ans 1:
query 1 : where condition is ture so result is expected whereas in
query 2 .. where conditon is false .
Ans 2 : 11683.84 kb
Answer to Q1:
query 1 : where condition is ture so result is expected whereas in
query 2 .. where conditon is false .
Answer to Q2:
11683.84 kb
Pinaldave sir .. What is the answer for the above one ?
Answer to Q1: The first query will handled internally like:
SELECT ‘SQLAuthority’ AS Statement11
WHERE ‘Authority’ = ‘Authority’ OR …. OR ‘Authority’ = NULL …..
So a null will not create a problem here as the first operands will either evaluate to true OR false. But the operand ‘Authority’ = null will neither evaluate to true nor false. It will evaluate to null only. So TRUE OR FALSE OR NULL is True.
The second query will be handled as below. Since we are using an “AND” operator and anything other than true in any of the operand will not give me any output.
SELECT ‘SQLAuthority’ AS Statement11
WHERE ‘Authority’ ‘S’ … AND ‘Authority’ NULL …..
‘Authority’ S is TRUE
‘Authority’ Q is TRUE
‘Authority’ L is TRUE
‘Authority’ NULL is NULL
So TRUE AND TRUE AND TRUE AND NULL –> NULL is not true so we have no output
Answer to Q2: 11686 KB
When SET ANSI_NULLS is ON, a SELECT statement that uses WHERE column_name = NULL returns zero rows even if there are null values in column_name. A SELECT statement that uses WHERE column_name NULL returns zero rows even if there are nonnull values in column_name
Looks like open/close brackets were taken out.
1. Query1 evaluates { where ‘Authority’ = ‘S’ OR ‘Authority’ = ‘Q’ OR ‘Authority’ = ‘L’ OR ‘Authority’ = ‘Authority’ } Since the last condition is true it returns true.
Query2 evaluates { where ‘Authority’ != ‘S’ OR ‘Authority’ != ‘Q’ OR ‘Authority’ != ‘L’ OR ‘Authority’ != null } Since ansi_nulls is turned on ‘Authority’ != null is unknown, so it evaluates to unknown and you get zero rows.
With Ansi_nulls on all comparisons against a null value evaluate to Unknown.
2. 11686.108398 Kilobyte
This was a fun exercise. Thanks for posting it :)
Hi Pinal,
Thank you so much. You know I’m very excited to get this prize….
Really glad to be of SQLAUTHORITY reader and participator……
Congrats chandrika and Cláudio Silva
Thanks Ram Kumar :)
Congrats to Chandrika!
You too Silva
Thank you Ram