Question

I must be overlooking something simple. I’m setting a variable from a query result in a MySQL stored procedure like this:

SELECT @myName := username FROM User WHERE ID=1; 

So, @myName is storing the username of userid 1, which is ‘Paul’. Great.

But later in the stored procedure I run an update on this record:

UPDATE User SET username = 'Fred' WHERE ID=1; 

Now, for some reason, @myName = ‘Fred’ when it should still equal ‘Paul’, right? It appears MySQL is just creating a pointer to the record rather than storing a static value in the @myName variable.

So in short, I want to be able to store a value in a variable from a query result and assure the value of my variable doesn’t change, even when the data in the table it was set from changes.

What am I missing? Thanks in advance!

Answer 1

That’s very surprising, I agree. I’m not sure how to explain it, but for what it’s worth, try this instead:

SELECT username INTO myName FROM User WHERE ID=1; 

See http://dev.mysql.com/doc/refman/5.0/en/select-into-statement.html

update: I’m trying to reproduce this problem, but I can’t. I’m using MySQL 5.0.51 on Mac OS X.

drop table if exists user; create table user (   id serial primary key,   username varchar(10) ); insert into user (username) values ('Paul');  drop procedure if exists doit; delimiter !! create procedure doit() begin   declare name varchar(10);   select @name:=username from user where id=1;   select @name; -- shows 'Paul' as expected   update user set username = 'Fred' where id=1;   select @name; -- still shows 'Paul' end!! delimiter ;  call doit(); 

Can you try the code above in your test database and let us know if it exhibits the problem you describe?