Transactions and locking 2007-11-12 - By Yves Goergen
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Hi,
there's very much information about how transactions and locking works
in InnoDB, but maybe there's also a simple and understandable answer to
my simple question:
When I start a transaction, then find the maximum value of a column and
use that + 1 to write a new row into the table, how do transactions
protect me from somebody else doing the same thing so that we'd both end
up writing a new row with the same value?
Here's a description:
BEGIN TRANSACTION
new_id := (SELECT MAX(id) FROM table) + 1
-- some more work here
INSERT INTO table (id, ...) VALUES (new_id, ...)
COMMIT
What happens if another user does the same in that "more work" region?
(Of course, this example is pseudocode, I really have a PHP application
that does this.)
--
Yves Goergen "LonelyPixel" <nospam.list@(protected)>
Visit my web laboratory at http://beta.unclassified.de
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