[FEATURE] Support for FULL OUTER UNION ALL BY NAME (Big Query)

[SusanaCastela]

Grammar or Syntax Description

BigQuery supports a non-standard extension to UNION ALL that includes FULL OUTER UNION ALL BY NAME. This construct allows combining multiple SELECT queries by matching column names instead of relying on column order, and filling in NULLs for missing columns.

Currently, JSQLParser does not support parsing this syntax. It results in the following error:
net.sf.jsqlparser.parser.ParseException: Encountered unexpected token: "FULL"

SQL Example

• Simplified Query Example, focusing on the failing feature:

  SELECT 1 as b FULL OUTER UNION ALL BY NAME SELECT 2 as a

Additional context

Database/Platform: Google BigQuery

Official Docs:
https://cloud.google.com/bigquery/docs/reference/standard-sql/query-syntax#union