[eftpotrm]

Because there's existing implementations that would interpret that as aliasing column names.

``` SELECT Field AS Renamed, OtherField AS AlsoRenamed ```

and

``` SELECT Field Renamed, OtherField AlsoRenamed ```

are semantically equivalent.

[yellowapple]

Making AS mandatory for naming columns would be an improvement in and of itself.

[eftpotrm]

Yes, but it's also a breaking change to a very large legacy codebase. I can't see it ever happening, sadly.