hook up seaweed sql engine

weed/server/postgres/protocol.go

@@ -66,15 +66,37 @@ func (s *PostgreSQLServer) handleMessage(session *PostgreSQLSession) error {
 func (s *PostgreSQLServer) handleSimpleQuery(session *PostgreSQLSession, query string) error {
 	glog.V(2).Infof("PostgreSQL Query (ID: %d): %s", session.processID, query)
 
-	// Translate PostgreSQL SQL to SeaweedFS SQL
-	translatedQuery, err := s.translator.TranslateQuery(query)
-	if err != nil {
-		return s.sendError(session, "42601", err.Error())
+	// Handle USE database commands for session context
+	queryUpper := strings.ToUpper(strings.TrimSpace(query))
+	if strings.HasPrefix(queryUpper, "USE ") {
+		parts := strings.Fields(query)
+		if len(parts) >= 2 {
+			newDatabase := strings.TrimSpace(parts[1])
+			session.database = newDatabase
+			s.sqlEngine.GetCatalog().SetCurrentDatabase(newDatabase)
+
+			// Send command complete for USE
+			err := s.sendCommandComplete(session, "USE")
+			if err != nil {
+				return err
+			}
+			return s.sendReadyForQuery(session)
+		}
 	}
 
-	// Execute using SQL engine
+	// Set database context in SQL engine if session database is different from current
+	if session.database != "" && session.database != s.sqlEngine.GetCatalog().GetCurrentDatabase() {
+		s.sqlEngine.GetCatalog().SetCurrentDatabase(session.database)
+	}
+
+	// Handle PostgreSQL-specific system queries
+	if postgresQuery := s.translatePostgreSQLSystemQuery(query); postgresQuery != "" {
+		query = postgresQuery
+	}
+
+	// Execute using SQL engine directly
 	ctx := context.Background()
-	result, err := s.sqlEngine.ExecuteSQL(ctx, translatedQuery)
+	result, err := s.sqlEngine.ExecuteSQL(ctx, query)
 	if err != nil {
 		return s.sendError(session, "42000", err.Error())
 	}
@@ -111,6 +133,57 @@ func (s *PostgreSQLServer) handleSimpleQuery(session *PostgreSQLSession, query s
 	return s.sendReadyForQuery(session)
 }
 
+// translatePostgreSQLSystemQuery translates essential PostgreSQL system queries
+// Only handles queries that PostgreSQL clients expect but SeaweedFS SQL engine doesn't natively support
+func (s *PostgreSQLServer) translatePostgreSQLSystemQuery(query string) string {
+	// Trim and normalize query
+	query = strings.TrimSpace(query)
+	query = strings.TrimSuffix(query, ";")
+	queryLower := strings.ToLower(query)
+
+	// Handle essential PostgreSQL system queries
+	switch queryLower {
+	case "select version()":
+		return "SELECT 'SeaweedFS 1.0 (PostgreSQL 14.0 compatible)' as version"
+	case "select current_database()":
+		return "SELECT '" + s.config.Database + "' as current_database"
+	case "select current_user":
+		return "SELECT 'seaweedfs' as current_user"
+	case "select current_setting('server_version')":
+		return "SELECT '14.0' as server_version"
+	case "select current_setting('server_encoding')":
+		return "SELECT 'UTF8' as server_encoding"
+	case "select current_setting('client_encoding')":
+		return "SELECT 'UTF8' as client_encoding"
+	}
+
+	// Handle pg_* catalog queries by mapping to equivalent SHOW commands
+	if strings.Contains(queryLower, "pg_tables") || strings.Contains(queryLower, "information_schema.tables") {
+		return "SHOW TABLES"
+	}
+	if strings.Contains(queryLower, "pg_database") || strings.Contains(queryLower, "information_schema.schemata") {
+		return "SHOW DATABASES"
+	}
+
+	// Handle transaction commands (no-op for read-only)
+	switch queryLower {
+	case "begin", "start transaction":
+		return "SELECT 'BEGIN' as status"
+	case "commit":
+		return "SELECT 'COMMIT' as status"
+	case "rollback":
+		return "SELECT 'ROLLBACK' as status"
+	}
+
+	// If starts with SET, return a no-op
+	if strings.HasPrefix(queryLower, "set ") {
+		return "SELECT 'SET' as status"
+	}
+
+	// Return empty string to use original query (let SQL engine handle it)
+	return ""
+}
+
 // handleParse processes a Parse message (prepared statement)
 func (s *PostgreSQLServer) handleParse(session *PostgreSQLSession, msgBody []byte) error {
 	// Parse message format: statement_name\0query\0param_count(int16)[param_type(int32)...]