Does SQL Server check for constraint violation when COMMIT is called?

If there are two different transactions, both of which update the username column to 'xyz' for userid = 234 in 'Users' table. This is a unique value for username. Ater this update each transaction adds a row to 'AppLog' table. The transaction is only committed after second operation.

The 'username' column has a unique constraint on it.

If transaction isolation level is 'read committed', and both transaction execute the first operation when neither of the transactions have been committed, then the transaction that calls COMMIT later will error out or not? If COMMIT does not check constraints then it will NOT error out. As a result we will have a violation of unique constraint happening without any error being thrown by SQL Server.

sun21170:

If COMMIT does not check constraints then it will NOT error out.

The statements that COMMIT causes to execute will be checked for contraint violations. If SQL Server allowed constraint violations, it wouldn't be around very long.

sql

does ms sql support two phase commit protocol

Hello ,
My question is:
does ms sql support two phase commit protocol?
and Why if no.
How if yes.
Thank youamoon.ljlj@.gmail.com wrote:

Quote:

Originally Posted by

Hello ,
My question is:
does ms sql support two phase commit protocol?
and Why if no.
How if yes.
Thank you

Yes. See Distributed Transaction Coordinator (aka MS DTC).

--
David Portas, SQL Server MVP

Whenever possible please post enough code to reproduce your problem.
Including CREATE TABLE and INSERT statements usually helps.
State what version of SQL Server you are using and specify the content
of any error messages.

SQL Server Books Online:
http://msdn2.microsoft.com/library/...US,SQL.90).aspx
--|||Microsoft SQL Server supports distributed transactions.

See this topic and the ones below it in the table of contents in the SQL
Server 2005 Books Online:
http://msdn2.microsoft.com/en-us/library/ms191440.aspx
BEGIN DISTRIBUTED TRANSACTION statement reference:
http://msdn2.microsoft.com/en-us/library/ms188386.aspx
--
Alan Brewer [MSFT]
SQL Server Documentation Team

Download the latest Books Online update:
http://www.microsoft.com/technet/pr...oads/books.mspx
This posting is provided "AS IS" with no warranties, and confers no rights.

Does Commit Transaction delete Temporary table?

Hi SQL Guru's,
I create a global temp table in one of my procedures:
select * into ##temp_update
from ( select distinct * from .....
after this I issue a commit transaction, and when I try to select from
the table I created (from my .Net code or Query Analyzer) it is not
there!
select * from ##temp_update
Invalid object name '##temp_update'.
Any idea why?From Books Online:
"Global temporary tables are automatically dropped when the session that
created the table ends and all other tasks have stopped referencing them. Th
e
association between a task and a table is maintained only for the life of a
single Transact-SQL statement. This means that a global temporary table is
dropped at the completion of the last Transact-SQL statement that was
actively referencing the table when the creating session ended."
If the session that creates the global temporary table ends before a new
session that accesses the global temporary table is started, the table is
dropped.
ML|||Yikes!
Good to know that, but bad for my program :)
thanks much
ML wrote:
> From Books Online:
> "Global temporary tables are automatically dropped when the session that
> created the table ends and all other tasks have stopped referencing them.
The
> association between a task and a table is maintained only for the life of
a
> single Transact-SQL statement. This means that a global temporary table is
> dropped at the completion of the last Transact-SQL statement that was
> actively referencing the table when the creating session ended."
> If the session that creates the global temporary table ends before a new
> session that accesses the global temporary table is started, the table is
> dropped.
>
> ML

Does Commit Transaction delete Temporary table?

Hi SQL Guru's,
I create a global temp table in one of my procedures:
select * into ##temp_update
from ( select distinct * from .....
after this I issue a commit transaction, and when I try to select from
the table I created (from my .Net code or Query Analyzer) it is not
there!
select * from ##temp_update
Invalid object name '##temp_update'.
Any idea why?From Books Online:
"Global temporary tables are automatically dropped when the session that
created the table ends and all other tasks have stopped referencing them. Th
e
association between a task and a table is maintained only for the life of a
single Transact-SQL statement. This means that a global temporary table is
dropped at the completion of the last Transact-SQL statement that was
actively referencing the table when the creating session ended."
If the session that creates the global temporary table ends before a new
session that accesses the global temporary table is started, the table is
dropped.
ML|||Yikes!
Good to know that, but bad for my program :)
thanks much
ML wrote:
> From Books Online:
> "Global temporary tables are automatically dropped when the session that
> created the table ends and all other tasks have stopped referencing them.
The
> association between a task and a table is maintained only for the life of
a
> single Transact-SQL statement. This means that a global temporary table is
> dropped at the completion of the last Transact-SQL statement that was
> actively referencing the table when the creating session ended."
> If the session that creates the global temporary table ends before a new
> session that accesses the global temporary table is started, the table is
> dropped.
>
> ML