support drop column and rename column

Author: sjjian

ast/ddl.go

@@ -33,4 +33,12 @@ type ColumnDefine struct {
 
 type ModifyColumnClause struct {
 	columnClause
+}
+
+type DropColumnClause struct {
+	columnClause
+}
+
+type RenameColumnClause struct {
+	columnClause
 }

lexer.go

@@ -182,6 +182,14 @@ var keywordMap = map[string]int{
 	"levels":        _levels,
 	"substitutable": _substitutable,
 	"force":         _force,
+	"columns":       _columns,
+	"continue":      _continue,
+	"unused":        _unused,
+	"constraints":   _constraints,
+	"invalidate":    _invalidate,
+	"online":        _online,
+	"checkpoint":    _checkpoint,
+	"rename":        _rename,
 }
 
 func init() {

parser_test.go

@@ -58,6 +58,15 @@ alter table db1.table1 add (id number default 123)
 `,
 		`
 alter table db1.table1 modify (id number default 123) 
+`,
+		`
+alter table db1.table1 drop column id
+`,
+		`
+alter table db1.table1 drop (id,name)
+`,
+		`
+alter table db1.table1 set unused column id
 `,
 	}
 	for _, query := range querys {