what the heck is the result of evaluating the inner query, in the outer expression?
Maybe I am missing something, but the exact meaning to vary a lot across different databases. Some seem to have a standalone "table" data type, while others don't.
I might be missing something as I'm self-taught, but the inner select specifies a set, and you "just" do a simple set membership test?
How it's implemented is as usual up to the database server implementation. Ones I've used creates a temporary table (like it does in so many other cases), and as such EXISTS is usually faster.
But I wouldn't rely on this when moving to another implementation, and use the query planner to see, just as I'd view the assembly output when moving to a new compiler.
Again, I don't have tons of experience, so concrete (counter) examples are welcome.
If I write
what the heck is the result of evaluating the inner query, in the outer expression?
Maybe I am missing something, but the exact meaning to vary a lot across different databases. Some seem to have a standalone "table" data type, while others don't.
I might be missing something as I'm self-taught, but the inner select specifies a set, and you "just" do a simple set membership test?
How it's implemented is as usual up to the database server implementation. Ones I've used creates a temporary table (like it does in so many other cases), and as such EXISTS is usually faster.
But I wouldn't rely on this when moving to another implementation, and use the query planner to see, just as I'd view the assembly output when moving to a new compiler.
Again, I don't have tons of experience, so concrete (counter) examples are welcome.