MySQL '@': what does it do?

Question

I'm following a tutorial here. It keeps using '@' characters in front of stuff. Can I just confirm... does '@' identify variables within a query?

Thanks,

James

Mario · Accepted Answer · 2010-11-12 19:18:11Z

2

SET is used to give the variable an initial value.

For example:

SET @row := 0;

SELECT (@row := @row + 1) AS row, name FROM table;

If we don't give the variable an initial value, it would be NULL.

answered Nov 12, 2010 at 19:18

Mario

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Bojangles Over a year ago

Thanks - perfect explanation. Welcome to Stackoverflow :)

AndreKR · Accepted Answer · 2010-11-12 16:58:44Z

2

It names a so-called "user variable".

http://dev.mysql.com/doc/refman/5.1/en/user-variables.html

answered Nov 12, 2010 at 16:58

AndreKR

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pavanred · Accepted Answer · 2010-11-12 16:58:47Z

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Yes, '@' is used as a prefix for user defined variables. Find more information here

answered Nov 12, 2010 at 16:58

pavanred

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BoltClock · Accepted Answer · 2010-11-12 16:59:23Z

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Yup. MySQL's documentation has a section about user-defined variables. You typically declare them with SET in MySQL, however I've seen other kinds of SQL use DECLARE.

answered Nov 12, 2010 at 16:59

BoltClock

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Amir Raminfar · Accepted Answer · 2010-11-12 17:00:46Z

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Ahh, this is actually how you declare variables in mysql. Look at here:

http://dev.mysql.com/tech-resources/articles/mysql-storedproc.html

The first thing we need to understand is how user variables are used and assigned values. A user variable is distinguished by having a '@' symbol in front of it, and values are assigned using the SET statement:

answered Nov 12, 2010 at 17:00

Amir Raminfar

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4 Comments

Amir Raminfar Over a year ago

@BoltClock - I do not appreciate rude comments. He never did mention in what context.

Bojangles Over a year ago

Intriguing - the tutorial I'm following uses stuff like SELECT @myRight := rgt FROM nested_category. Is that OK to use too?

BoltClock Over a year ago

Figured as much. I admit I was rather impatient, so I'll apologize. @JamWaffles, you may want to add an example snippet so it's clearer what you're referring to.

Bojangles Over a year ago

My bad - sorry to both of you :-) The original question, however, has been answered many times in this thread.

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