Does UPDATE overwrite values if they are identical?

Question

I only want to update a vale in my database if it is different. Reading through the Oracle docs on UPDATE, it says...

...the UPDATE statement updates columns of existing rows in the named table with new values.

Since it doesn't say it won't overwrite identical values, should I take this statement literally? Does this mean MySQL does some sort of Boolean matching check for me?

Answer 1

No, MySQL won't overwrite identical values.

Lets say we insert some data:

insert into foo(id,val1,val2,val3) values (0,1,2,3);
Query OK, 1 row affected (0.00 sec)

If you update it with the same values:

update foo set id=0, val1=1, val2=2, val3=3 where id=0;
Query OK, 0 rows affected (0.00 sec)
Rows matched: 1  Changed: 0  Warnings: 0

Take a look on servers response 0 rows affected