Apache ShardingSphere: Solve unsupported Postgres sql about alter statement for ShardingSphere Parser

Apache ShardingSphere
Apache ShardingSphere is positioned as a Database Plus, and aims at building a standard layer and ecosystem above heterogeneous databases. It focuses on how to reuse existing databases and their respective upper layer, rather than creating a new database. The goal is to minimize or eliminate the challenges caused by underlying databases fragmentation.
Page: https://shardingsphere.apache.org
Github: https://github.com/apache/shardingsphere

 Background

ShardingSphere parser engine helps users parse a SQL to get the AST (Abstract Syntax Tree) and visit this tree to get SQLStatement (Java Object). At present, this parser engine can handle SQLs for `MySQL`, `PostgreSQL`, `SQLServer`, `openGauss` and `Oracle`, which means we have to understand different database dialect SQLs.
More details:
https://shardingsphere.apache.org/document/current/en/reference/sharding/parse/

Task

This issue is to solve the unsupported postgres sql about alter in this file . * ALTER OPERATOR

• ALTER POLICY

• ALTER PUBLICATION

• ALTER ROUTINE

• ALTER RULE

• ALTER SCHEMA

• ALTER SEQUENCE

• ALTER SERVER

• ALTER STATISTICS

• ALTER SUBSCRIPTION

• ALTER TABLE

• ALTER TEXT SEARCH

• ALTER TRIGGER

• ALTER TYPE

• ALTER VIEW

You can learn more here. *
You may need to try to get why it's not supported.(antlr4 grammar? or not implement visit method) You can use antlr4 plugins to help you to analyze. You may need to visit an official doc to check the grammar.

• 
  After you fix it, remember to add a new corresponding SQL case in SQL Cases and the expected parsed result in Expected Statment XML.

• Run SQLParserParameterizedTest and UnsupportedSQLParserParameterizedTest to make sure no exceptions.

Notice, these issues can be a good example.
support alter foreign table for pg/og
support alter materialized view for pg/og.

Relevant Skills

1. Master JAVA language
2. Have a basic understanding of Antlr g4 file
3. Be familiar with Postgres SQLs

Targets files

1. Postgres SQLs g4 file: https://github.com/apache/shardingsphere/blob/master/shardingsphere-sql-parser/shardingsphere-sql-parser-dialect/shardingsphere-sql-parser-postgresql/src/main/antlr4/org/apache/shardingsphere/sql/parser/autogen/PostgreSQLStatement.g4

Mentor

Trista Pan, PMC of Apache ShardingSphere, https://tristazero.github.io

Zhengqiang Duan, Committer of ApacheShardingSphere, https://github.com/strongduanmu