Can you explain this string to me?

It depends on what you're trying to do. So, if you leave the WHERE off of the initial, it will do what you were thinking initially, find all the instances of California and replace it with CA and display it that way. The WHERE Replace doesn't do anything at that point as it has already changed that in the query results.

If you do want to get the state displaying how it does and only select specific columns, you can just SELECT street, city, state, zip FROM addresses WHERE REPLACE(state, "California", "CA") = "CA"; and it will work the same as how the example does.

Basically, what it all comes down to is how you want to display the results of the Query. When displaying to a user, you may just want it to show all of them as CA, but there may be a reason you want to see the actual original data if you're just doing the Query for yourself.

To be honest, there's a few ways to get the results based on the data in the example, as it's a pretty simple example. But, it becomes more useful when the Query is more complicated. For instance, if I wanted to see all the ones that are listed as California and CA, I would likely just do a SELECT * FROM addresses WHERE state IN('California', 'CA'); This returns the same thing and is obviously less typing, but again, it really depends on what your situation is.

It's a good thing to keep in the tool box in case you ever run into something that might be better served by a Query like that. One of the nice things about SQL, once you get the hang of it, is that it can be pretty flexible on how to get results, and some ways will be better than others depending on the situation. I hope this helps some!