How useful can "LIMIT 1" be?

[Nhoj]

I've got a database with well over 500,000 users all stored in a table named `users`. The table itself has around 20 - 25 columns with some information stored in each column such as e-mail etc. The primary column is called 'id' and it's stored as an unsigned int(11) with auto incrementing.

I was wondering, if I am updating my database and only update 1 users information at a time based on their ID would the "LIMIT 1" argument help increase load time or reduce any overhead?

For example, would running [code=php:0]mysql_query('UPDATE `users` SET `uAddress` = "'.$_POST['uAddress'].'" WHERE `uID` = '.$uID.' LIMIT 1');[/code]

be any faster than running

[code=php:0]mysql_query('UPDATE `users` SET `uAddress` = "'.$_POST['uAddress'].'" WHERE `uID` = '.$uID);[/code]

Thanks,
John

[fenway]

With a UID, limit 1 is redundant.

[hvle]

even though it might be redundant, you should place limit to every update and delete statements.  It added another shield to protect your data.

[fenway]

I disagree... there's no reason to protect a primary key.

[hvle]

You are absolutely right, but it is a good coding pratice to have limit 1 on update and delete queries.

[fenway]

IMHO, I don't like LIMIT 1 where it's not really needed, because it allows for poor queries to be go unnoticed.