In SQL Server what does SET ANSI NULLS ON mean

Question

The definition says      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  lt   NULL returns zero rows even if there are non-null values in column name    Does this mean that no nulls will be included in this query   SELECT Region FROM employees WHERE Region    region   Or do ANSI NULLs concern only queries like this one  where the WHERE includes the specific word NULL    SELECT Region FROM employees WHERE Region   NULL

User · Answer

I guess the main thing here is   Never user     anything   NULL   anything  lt  gt  NULL  anything    null   Always use     anything IS NULL   anything IS NOT NULL

User · Answer

It means that no rows will be returned if  region is NULL  when used in your first example  even if there are rows in the table where Region is NULL  When ANSI NULLS is on  which you should always set on anyway  since the option to not have it on is going to be removed in the future   any comparison operation where  at least  one of the operands is NULL produces the third logic value - UNKNOWN  as opposed to TRUE and FALSE   UNKNOWN values propagate through any combining boolean operators if they re not already decided  e g  AND with a FALSE operand or OR with a TRUE operand  or negations  NOT   The WHERE clause is used to filter the result set produced by the FROM clause  such that the overall value of the WHERE clause must be TRUE for the row to not be filtered out  So  if an UNKNOWN is produced by any comparison  it will cause the row to be filtered out    user1227804 s answer includes this quote   If both sides of the comparison are columns or compound expressions  the setting does not affect the comparison   from SET ANSI NULLS  However  I m not sure what point it s trying to make  since if two NULL columns are compared  e g  in a JOIN   the comparison still fails  create table  T1       ID int not null      Val1 varchar 10  null   insert into  T1 ID Val1  select 1 null  create table  T2       ID int not null      Val1 varchar 10  null   insert into  T2 ID Val1  select 1 null  select   from  T1 t1 inner join  T2 t2 on t1 ID   t2 ID and t1 Val1   t2 Val1  The above query returns 0 rows  whereas  select   from  T1 t1 inner join  T2 t2 on t1 ID   t2 ID and  t1 Val1   t2 Val1 or t1 Val1 is null and t2 Val1 is null   Returns one row  So even when both operands are columns  NULL does not equal NULL  And the documentation for   doesn t have anything to say about the operands   When you compare two NULL expressions  the result depends on the ANSI NULLS setting  If ANSI NULLS is set to ON  the result is NULL1  following the ANSI convention that a NULL  or unknown  value is not equal to another NULL or unknown value  If ANSI NULLS is set to OFF  the result of NULL compared to NULL is TRUE  Comparing NULL to a non-NULL value always results in FALSE2   However  both 1 and 2 are incorrect - the result of both comparisons is UNKNOWN    The cryptic meaning of this text was finally discovered years later  What it actually means is that  for those comparisons  the setting has no effect and it always acts as if the setting were ON  Would have been clearer if it had stated that SET ANSI NULLS OFF was the setting that had no affect

User · Answer

https   docs microsoft com en-us sql t-sql statements set-ansi-nulls-transact-sql  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  lt   NULL returns zero rows even if there are nonnull values in column name   For e g  DECLARE  TempVariable VARCHAR 10  SET  TempVariable   NULL  SET ANSI NULLS ON SELECT  NO ROWS IF SET ANSI NULLS ON  where     TempVariable   NULL -- IF ANSI NULLS ON   RETURNS ZERO ROWS   SET ANSI NULLS OFF SELECT  THERE WILL BE A ROW IF ANSI NULLS OFF  where     TempVariable  NULL -- IF ANSI NULLS OFF   THERE WILL BE ROW

User · Answer

SET ANSI NULLS ON  IT Returns all values including null values in the table  SET ANSI NULLS off   it Ends when  columns contains null values

User · Answer

If  Region is not a null value  lets say  Region    South   it will not return rows where the Region field is null  regardless of the value of ANSI NULLS   ANSI NULLS will only make a difference when the value of  Region is null  i e  when your first query essentially becomes the second one   In that case  ANSI NULLS ON will not return any rows  because null   null will yield an unknown boolean value  a k a  null   and ANSI NULLS OFF will return any rows where the Region field is null  because null   null will yield true

User · Answer

Set ANSI NULLS OFF will make NULL   NULL comparision return true  EG            SET ANSI NULLS OFF         select   from sys tables         where principal id   Null   will return some result as displayed below  zcwInvoiceDeliveryType  744547  NULL zcExpenseRptStatusTrack 2099048 NULL ZCVendorPermissions 2840564 NULL ZCWOrgLevelClientFee    4322525 NULL  While this query will not return any results           SET ANSI NULLS ON          select   from sys tables         where principal id   Null

User · Answer

If ANSI NULLS is set to  ON   and if we apply      lt   on NULL column value while writing select statement then it will not return any result   Example  create table  tempTable  sn int  ename varchar 50    insert into  tempTable values  1   Manoj     2   Pankaj     3  NULL    4   Lokesh     5   Gopal     SET ANSI NULLS ON  select   from  tempTable where ename is NULL --  1 row s  affected  select   from  tempTable where ename   NULL --  0 row s  affected  select   from  tempTable where ename is not NULL --  4 row s  affected  select   from  tempTable where ename  lt  gt  NULL --  0 row s  affected    SET ANSI NULLS OFF  select   from  tempTable where ename is NULL --  1 row s  affected  select   from  tempTable where ename   NULL --  1 row s  affected  select   from  tempTable where ename is not NULL --  4 row s  affected  select   from  tempTable where ename  lt  gt  NULL --  4 row s  affected

[sql] In SQL Server, what does "SET ANSI_NULLS ON" mean?

Examples related to sql

Examples related to tsql

Examples related to stored-procedures