Question

I wrote a sql join query in oracle with two table.
While writing query I did not use any table alias to refer column in select clause.
Now this was possible because the selected columns were having different names in both the tables.

So the question follows; is it necessary (from performance point of view) to use a table alias to select column regardless there is any similar column name in both the tables?

Please note: Right now I am under impression that “In case of join query when we do not specify table alias to select column oracle will always lookup the table metadata to find out which table has this column.” So is my assumption true?

Thanks,
hanumant

Answer 1

No, your assumption is not true.

There are at least four reasons to use table aliases:

• If the alias is shorter than the name it allows you to type less.
• If you self-join a table you are required to give an alias to one or both of the tables to allow you to distinguish between them.
• Derived tables must have an alias in some database systems (not Oracle though, I think).
• The alias can make it clearer what the role of the table is in that particularly query.

There is no significant performance penalty from using them.