MySQL: How to swap entires of two columns with just one query

tobi — Wed, 24 Jun 2009 13:16:29 +0000

Check this out, I found out a really nice way how to swap values of two columns with just one query, using user defined variables. Given a table with two columns a and b. To swap their values in whole, use this query:

UPDATE my_table SET a=@tmp:=a, a=b, b=@tmp;

Done! Isn’t that easy?

MySQL User defined Variables – good thing to know!

tobi — Thu, 02 Apr 2009 12:59:54 +0000

Have you ever heard of user defined variables in MySQL? I hadn’t and nearly freaked out when I found out. That’s the thing I was always looking for, that’s so cool, and fasten up your SQL live a lot!

Now, renumbering a table is as easy as never before:

Set @a = 0;
UPDATE my_table SET id=@a:=@a+1

Check out the docu and examples:

http://dev.mysql.com/doc/refman/5.0/en/user-variables.html

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MySQL: How to swap entires of two columns with just one query

MySQL User defined Variables – good thing to know!