Is it better to use column aliases with or without the keyword AS?

Question

Which is best?

Select TestColumn TC

or

Select TestColumn AS TC

I prefer the first one but I am not sure if this is a modern way of declaring the alias.

Answer 1

The two are equivalent for most purposes. I prefer the explicit AS notation.

One reason why I use the AS form is because, in the DBMS I use mainly, it provides a measure of protection against new keywords appearing on system upgrades. That is:

SELECT TestColumn KeyWord

where 'KeyWord' becomes a keyword in a future release can cause problems, whereas in the particular system, using:

SELECT TestColumn AS KeyWord

remains valid.

I recently learned (was told) that Oracle does not support AS in table aliases.

FROM TableName T1     -- OK in Oracle
FROM TableName AS T1  -- Not OK in Oracle

If that is accurate (I've not validated it), then I regard that AS a bug.

It's your choice, though; the two notations are equivalent.

Answer 2

I prefer the second one (using "AS"). If it works either way, just use what you prefer and use it consistently.