title: SQL Update set from another table where fields are not equal
body: <p>Let's say I have 2 tables <code>USER1(id, first, last)</code> and <code>USER2(id, first, last)</code>. I want to write a query to update <code>USER1</code> by selecting from <code>USER2</code> on 1.id = 2.id and only update the fields, which are different. For example, only update first when first(s) are different. Please help.</p>