Major Description
As the discussion in http://apache-spark-developers-list.1001551.n3.nabble.com/DISCUSS-PostgreSQL-dialect-td28417.html, we need to remove PostgreSQL dialect form code base for several reasons:
1. The current approach makes the codebase complicated and hard to maintain.
2. Fully migrating PostgreSQL workloads to Spark SQL is not our focus for now.
Curently we have 3 features under PostgreSQL dialect:
1. SPARK-27931: when casting string to boolean, `t`, `tr`, `tru`, `yes`, .. are also allowed as true string.
2. SPARK-29364: `date - date` returns interval in Spark (SQL standard behavior), but return int in PostgreSQL
3. SPARK-28395: `int / int` returns double in Spark, but returns int in PostgreSQL. (there is no standard)