Question: I have a performance-related question. Let's say I have a user with first name Michael. Take the following query:

```
UPDATE users
SET first_name = 'Michael'
WHERE users.id = 123

```

Will the query actually execute the update, even though it is being updated to the same value? If so, how do I prevent it from happening?

Answer: 
ORM's like Ruby on Rail's offer deferred execution which mark a record as changed (or not) and then when needed or called, then submit the change to the database.

PostgreSQL is a database and not an ORM. It would have decreased performance if it took the time to check if a new value was the same as the updated value in your query.

It will therefore update the value regardless of whether it is the same as the new value or not.

If you wish to prevent this, you could use code like Max Vernon suggested in his answer.
**From a database point of view**

The answer to your question is YES. The update will take place. The database does not check the previous value, it only sets the new value.

As this happen in memory (and will only be written to the datafiles after a commit is issued) the performance would not be an issue.

**From an ORM perspective**

Normally you will have an Object representing a single row of the database (it can be a lot more complex than that, but let's keep it simple). This object is managed in memory (at the app server level) and only the latest commited version of that object will actually make it to the database at a certain point.

That may explain the different behaviour.

Now, let's not compare a cargo ship with a 3D printer. The fact that you can send 3D printers using cargo ships doesn't mean that there may be any kind of comparison between them.

Enjoy!

I hope this clarified some concepts.