In the following statement (PostgreSQL 11):
=> SELECT c cost FROM tt; ERROR: syntax error at or near "cost" LINE 1: SELECT c cost FROM tt;
I get an error. Adding parenthesis around the field expression doesn't help (
SELECT (c) cost FROM tt;). But adding the
AS keyword fixes it.
=> SELECT c AS cost FROM tt; cost ------ 1 ...
I realize that
cost is a keyword, but my impression is that the
AS keyword is optional.
From a language perspective, why is the
AS keyword required (or helpful) here? Is the PostgreSQL behavior here standard or documented somewhere?
Are there any other cases when the
AS keyword is required?