Excuse the noob question, I couldn’t find any reading material on this topic.
Let’s say my_table has two fields, pkey_id and another_id. The primary key is pkey_id and of course indexed.
Then someone adds a composite index on btree(pkey_id, another_id).
Question 1) Is there any benefit to having pkey_id in the second index (assuming the index was created to satisfy some arbitrary WHERE clause)?
Question 2) Regardless of the answer to Question 1 - if another_id is not guaranteed to be unique, whereas pkey_id is – there any value to changing the order of declaration (more generally, is there a performance impact for column ordering in btree composite keys?)
Thanks,
Carlo
