DROP DEFAULT cannot be parsed

[jackiezh]

Describe the bug
ALTER COLUMN xxx DROP DEFAULT cannot be parsed.

To Reproduce
Steps to reproduce the behavior:

1. Example SQL
   ALTER TABLE table_a ALTER COLUMN col_a DROP DEFAULT;
   ALTER TABLE table_a ALTER col_a DROP DEFAULT;

2. Parsing this SQL using JSqlParser with this statements
   analizeSQL("ALTER TABLE table_a ALTER COLUMN col_a DROP DEFAULT");
   analizeSQL("ALTER TABLE table_a ALTER col_a DROP DEFAULT");

3. Exception
   // analizeSQL("ALTER TABLE table_a ALTER COLUMN col_a DROP DEFAULT");
   net.sf.jsqlparser.parser.ParseException: Encountered unexpected token: "DEFAULT" "DEFAULT"
   at line 1, column 45.

Was expecting one of:

"NOT"
"NULL"

at net.sf.jsqlparser.parser.CCJSqlParser.generateParseException(CCJSqlParser.java:31468)
at net.sf.jsqlparser.parser.CCJSqlParser.jj_consume_token(CCJSqlParser.java:31301)
at net.sf.jsqlparser.parser.CCJSqlParser.AlterExpressionColumnDropNotNull(CCJSqlParser.java:16732)
at net.sf.jsqlparser.parser.CCJSqlParser.AlterExpression(CCJSqlParser.java:17027)
at net.sf.jsqlparser.parser.CCJSqlParser.AlterTable(CCJSqlParser.java:17947)
at net.sf.jsqlparser.parser.CCJSqlParser.SingleStatement(CCJSqlParser.java:267)
at net.sf.jsqlparser.parser.CCJSqlParser.Statement(CCJSqlParser.java:153)
at net.sf.jsqlparser.parser.CCJSqlParserUtil.parseStatement(CCJSqlParserUtil.java:188)

// analizeSQL("ALTER TABLE table_a ALTER col_a DROP DEFAULT");
net.sf.jsqlparser.parser.ParseException: Encountered unexpected token: "DROP" "DROP"
at line 1, column 33.

Was expecting:

"COMMENT"

at net.sf.jsqlparser.parser.CCJSqlParser.generateParseException(CCJSqlParser.java:31468)
at net.sf.jsqlparser.parser.CCJSqlParser.jj_consume_token(CCJSqlParser.java:31301)
at net.sf.jsqlparser.parser.CCJSqlParser.AlterExpression(CCJSqlParser.java:17489)
at net.sf.jsqlparser.parser.CCJSqlParser.AlterTable(CCJSqlParser.java:17947)
at net.sf.jsqlparser.parser.CCJSqlParser.SingleStatement(CCJSqlParser.java:267)
at net.sf.jsqlparser.parser.CCJSqlParser.Statement(CCJSqlParser.java:153)
at net.sf.jsqlparser.parser.CCJSqlParserUtil.parseStatement(CCJSqlParserUtil.java:188)

System

• Database you are using: PostgreSQL
• Java Version: java-1.8
• JSqlParser version: 4.4

[manticore-projects]

True, not implemented yet -- although a similar DROP NOT NULL exists.