[marzell]

You absolutely can in many engines, for instance in Snowflake... with the small exception that in all supporting engines you actually need to use HAVING instead of WHERE in your second example (because it compares an aggregation, otherwise WHERE is fine).

You can also use "correlated column aliases" (I can't recall the proper name) i.e.

    SELECT
        id AS foo,
        foo || '_1' as foo_n,
        right(foo_n, 1) as foo_ordinal
    FROM MyTable
    WHERE foo = 1;

Again, if this isn't all part of SQL standards, the reality is that a lot of engines have semi-standard (sometimes very proprietary too) ways of handling these now common patterns. For real-world use cases, the standards are unfortunately becoming increasingly irrelevant. I think it would be better in the long term to use standards, but if they can't keep up with actual usage then they will just get ignored.