There's hardly anything to add to this awesome post, except maybe:
"I don't maintain the database; I just query it!" folks, don't be scared off!
Even if you don't have tools that show you the indexes, it's always good to ask your DBA (or some other expert) where the indexes are in tables you plan to join with SQL (or a drag-and-drop tool that generates SQL behind the scenes), so that you can potentially write faster queries.
I say "potentially" because the index won't always make your query run faster (it depends on the data and on your query). But that's the subject of a 3-hour university lecture and exercises doing "explain plan" with pencil and paper ... :-)
A good guess, if you're in a rush, is that the "primary key" for a table is often indexed to make "joining" it to other tables against "foreign keys" faster. In other words, join tables the way they seem intuitively related to each other, those joins may run reasonably quickly.
But ask your DBA or other database expert to be sure.
Thanks Katie :)
Great advice to check in with your DBA before making those kinds of decisions. There's often a lot more going on behind the scenes and other indexes may have been applied for different reasons. An index may make things go faster, but there could be another way to solve the problem.
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