如何防止SQL同时运行事务

Question

I've noticed that MS SQL may begin another transaction just before a previous transaction is complete (or committed). Is there a way how we can ensure a transaction must complete first before the next transaction begins?

My problem is that I want to perform an SQL SELECT almost immediately after an SQL INSERT. What I'm seeing right now is; when the SELECT statement is run; it does not return the (very) recently inserted data.

As I traced this scenario using SQL profiler, I've noticed that the SQL INSERT and SELECT performs simultaneously, as in the SELECT occurs before the INSERT is completed.

Is there a way to fix this problem of mine? thanks!

Answer 1

From the sounds of it, you're looking for the OUTPUT clause

From the examples in the documentation http://msdn.microsoft.com/en-us/library/ms177564.aspx

DECLARE @MyTableVar table( NewScrapReasonID smallint,
                           Name varchar(50),
                           ModifiedDate datetime);
INSERT Production.ScrapReason
    OUTPUT INSERTED.ScrapReasonID, INSERTED.Name, INSERTED.ModifiedDate
        INTO @MyTableVar
VALUES (N'Operator error', GETDATE());

Answer 2

You can run your transactions in SERIALIZABLE isolation level. In this way you will ensure that the select will be performed after the insert. In lower isolation levels, the select is performed in paralell and returns the snapshot of the data - the way it is seen with all transactions completed before the one that issues select has been started.

Answer 3

I'm guessing you want to get an auto-generated identifier back after the insert? I'm not sure the MSSQL way to do this, but in PostgreSQL, there is INSERT ... RETURNING extension to solve exactly this problem.

http://www.postgresql.org/docs/9.1/static/sql-insert.html

Are you locked into MSSQL?