Marcus wrote:[color=blue]
> Hello,
>
> I have 2 questions regarding InnoDB tables:
>
> 1. In the MySQL manual, it states that
> "MySQL begins each client connection with autocommit mode enabled by
> default. When autocommit is enabled, MySQL does a commit after each SQL
> statement if that statement did not return an error."
>
> Does using BEGIN override this behavior? In other words, with
> autocommit on, does BEGIN open up a new transaction and stop committing
> until an explicit COMMIT command? Or do I need to turn autocommit off
> before multi-query transactions?[/color]
Perhaps you are looking in another manual. The official online manual is
rather clear on that.
http://dev.mysql.com/doc/mysql/en/in...utocommit.html
[quote]
If the connection has autocommit enabled, the user can still perform a
multiple-statement transaction by starting it with an explicit START
TRANSACTION or BEGIN statement and ending it with COMMIT or ROLLBACK.
[end quote]
So, yes, yes and no.
[color=blue]
> 2. I have been reading the examples for LOCK IN SHARE MODE and FOR
> UPDATE in the manual, but I am still confused as to when I should use
> one as opposed to the other. I have gone through tutorials but many
> just use the same examples as the manual. I'm sure I'm just missing
> something small, but if someone could give a simple example of the
> difference between the two, that would be very helpful as the difference
> to me seems very suttle.[/color]
Not sure what examples would be better than the ones in the manual, they
are probably as good as they get. I assume you read this page:
http://dev.mysql.com/doc/mysql/en/in...ing-reads.html
It is not the real/whole story, but perhaps it is easier if you see it
like:..
"FOR UPDATE" is used when you have the intention of updating the rows in
the table you select from, and "LOCK IN SHARE MODE" is used when they
(the selected rows) just are needed for an update elsewhere, and reading
can be shared by many.
/Bent
