feat(parser): add Oracle CONNECT BY / START WITH hierarchical query support (#450)

Extend the MariaDB CONNECT BY / START WITH hierarchical query parser to also
activate for Oracle dialect. Update isMariaDBClauseStart() to guard table-alias
parsing for both dialects, preventing START WITH / CONNECT BY from being
misidentified as aliases.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: 2 people

pkg/sql/parser/mariadb.go

@@ -29,10 +29,10 @@ func (p *Parser) isMariaDB() bool {
 }
 
 // isMariaDBClauseStart returns true when the current token is the start of a
-// MariaDB hierarchical-query clause (CONNECT BY or START WITH) rather than a
-// table alias. Used to guard alias parsing in FROM and JOIN table references.
+// MariaDB or Oracle hierarchical-query clause (CONNECT BY or START WITH) rather
+// than a table alias. Used to guard alias parsing in FROM and JOIN table references.
 func (p *Parser) isMariaDBClauseStart() bool {
-	if !p.isMariaDB() {
+	if !p.isMariaDB() && p.dialect != string(keywords.DialectOracle) {
 		return false
 	}
 	val := strings.ToUpper(p.currentToken.Token.Value)

pkg/sql/parser/parser_connectby_test.go

@@ -0,0 +1,107 @@
+// Copyright 2026 GoSQLX Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package parser_test
+
+import (
+	"testing"
+
+	"github.com/ajitpratap0/GoSQLX/pkg/gosqlx"
+	"github.com/ajitpratap0/GoSQLX/pkg/sql/ast"
+	"github.com/ajitpratap0/GoSQLX/pkg/sql/keywords"
+)
+
+// TestConnectBy_Oracle_Basic tests basic Oracle CONNECT BY syntax.
+func TestConnectBy_Oracle_Basic(t *testing.T) {
+	sql := `SELECT employee_id, manager_id, name
+	        FROM employees
+	        START WITH manager_id IS NULL
+	        CONNECT BY PRIOR employee_id = manager_id`
+	tree, err := gosqlx.ParseWithDialect(sql, keywords.DialectOracle)
+	if err != nil {
+		t.Fatalf("Parse() error: %v", err)
+	}
+	sel, ok := tree.Statements[0].(*ast.SelectStatement)
+	if !ok {
+		t.Fatalf("expected SelectStatement, got %T", tree.Statements[0])
+	}
+	if sel.ConnectBy == nil {
+		t.Error("expected ConnectBy clause to be populated")
+	}
+	if sel.StartWith == nil {
+		t.Error("expected StartWith expression to be populated")
+	}
+}
+
+// TestConnectBy_Oracle_NoCycle tests Oracle CONNECT BY with NOCYCLE modifier.
+func TestConnectBy_Oracle_NoCycle(t *testing.T) {
+	sql := `SELECT id, parent_id FROM categories
+	        START WITH parent_id IS NULL
+	        CONNECT BY NOCYCLE PRIOR id = parent_id`
+	tree, err := gosqlx.ParseWithDialect(sql, keywords.DialectOracle)
+	if err != nil {
+		t.Fatalf("Parse() error: %v", err)
+	}
+	sel, ok := tree.Statements[0].(*ast.SelectStatement)
+	if !ok {
+		t.Fatalf("expected SelectStatement, got %T", tree.Statements[0])
+	}
+	if sel.ConnectBy == nil {
+		t.Fatal("expected ConnectBy")
+	}
+	if !sel.ConnectBy.NoCycle {
+		t.Error("expected NoCycle = true")
+	}
+}
+
+// TestConnectBy_Oracle_ConnectByOnly tests CONNECT BY without START WITH.
+func TestConnectBy_Oracle_ConnectByOnly(t *testing.T) {
+	sql := `SELECT id, parent_id FROM categories
+	        CONNECT BY PRIOR id = parent_id`
+	tree, err := gosqlx.ParseWithDialect(sql, keywords.DialectOracle)
+	if err != nil {
+		t.Fatalf("Parse() error: %v", err)
+	}
+	sel, ok := tree.Statements[0].(*ast.SelectStatement)
+	if !ok {
+		t.Fatalf("expected SelectStatement, got %T", tree.Statements[0])
+	}
+	if sel.ConnectBy == nil {
+		t.Error("expected ConnectBy clause")
+	}
+	if sel.StartWith != nil {
+		t.Error("expected StartWith to be nil when not specified")
+	}
+}
+
+// TestConnectBy_MariaDB_StillWorks ensures existing MariaDB CONNECT BY parsing remains intact.
+func TestConnectBy_MariaDB_StillWorks(t *testing.T) {
+	sql := `SELECT id, parent_id FROM categories
+	        START WITH parent_id IS NULL
+	        CONNECT BY PRIOR id = parent_id`
+	tree, err := gosqlx.ParseWithDialect(sql, keywords.DialectMariaDB)
+	if err != nil {
+		t.Fatalf("Parse() error: %v", err)
+	}
+	sel, ok := tree.Statements[0].(*ast.SelectStatement)
+	if !ok {
+		t.Fatalf("expected SelectStatement, got %T", tree.Statements[0])
+	}
+	if sel.ConnectBy == nil {
+		t.Error("expected ConnectBy clause")
+	}
+	if sel.StartWith == nil {
+		t.Error("expected StartWith expression")
+	}
+}

pkg/sql/parser/select.go

@@ -109,8 +109,8 @@ func (p *Parser) parseSelectStatement() (ast.Statement, error) {
 		return nil, err
 	}
 
-	// MariaDB: START WITH ... CONNECT BY hierarchical queries (10.2+)
-	if p.isMariaDB() {
+	// Oracle/MariaDB: START WITH ... CONNECT BY hierarchical queries
+	if p.isMariaDB() || p.dialect == string(keywords.DialectOracle) {
 		if strings.EqualFold(p.currentToken.Token.Value, "START") {
 			p.advance() // Consume START
 			if !strings.EqualFold(p.currentToken.Token.Value, "WITH") {