Support Projection Aliases

[niryarden]

Problem:

Adding an alias to a projection in the SELECT clause is a pretty standard syntax:

SELECT count(*) AS table_size FROM Table

However, the evaluator breaks when trying to parse this kind of query.

Reproduce:

I went to the gold.txt file and changed the 3rd row from

SELECT Country FROM AIRLINES WHERE Airline  =  "JetBlue Airways"	flight_2

to

SELECT Country AS my_c FROM AIRLINES WHERE Airline  =  "JetBlue Airways"	flight_2`

When running

python evaluation.py --gold evaluation_examples/gold.txt --pred evaluation_examples/predict.txt --db database --etype match --plug_value --table tables.json

parse_sql crashed with:

AssertionError: Error col: as

thrown from parse_col when searching for the the not existing 'as' column in the schema.

[sorgfresser]

The same happens upon using strftime in the select. I was able to produce AssertionError: Error col: strftime using the test set of EHRSQL.
With the query

select strftime('%j',admissions.dischtime) - strftime('%j',admissions.admittime) from admissions where admissions.subject_id = 85169 and admissions.dischtime is not null order by admissions.admittime asc limit 1

This is somewhat more niche as strftime is SQLite syntax, but since Spider uses SQLite I was a bit surprised that this error occurred.

[sorgfresser]

I adapted the whole test suite to use sqlglot in my fork now, so I can use strftime and projection aliases as well. Maybe it's also interesting for you.