Only What Needs Updating

Update Only What Needs Updating

Let’s take the example of normalizing an e-mail column:

db= UPDATE users SET email = lower(email);
UPDATE 1010000
Time: 1583.935 ms (00:01.584)

But what happens if the email address is already all lowercase? We’ve done some extra work for nothing.

To counter this, let’s add a WHERE clause, so the database knows it doesn’t have to do an update on some columns:

~5 times faster!

db= UPDATE users SET email = lower(email)
db- WHERE email != lower(email);
UPDATE 10000
Time: 299.470 ms