fix:add server_id system variable for odbc (#23578)

Adds the missing server_id system variable to MatrixOne so ODBC clients can read @@server_id during connection initialization without error. Also adds regression coverage in the distributed system variable tests. This prevents Tableau/ODBC connections from failing with “system variable does not exist.”

Approved by: @fengttt, @heni02, @XuPeng-SH

Author: robll-v1

pkg/frontend/variables.go

@@ -970,6 +970,18 @@ func useTomlConfigOverOtherConfigs(CNServiceConfig *config.FrontendParameters, s
 	sysVarsMp["version"] = verPrefix + verVal
 }
 
+func resolveServerID(ses *Session) string {
+	if ses == nil {
+		return ""
+	}
+	rm := ses.getRoutineManager()
+	if rm == nil || rm.baseService == nil {
+		return ""
+	}
+	serviceID := rm.baseService.ID()
+	return serviceID
+}
+
 // Get return sys vars of accountId
 func (m *GlobalSysVarsMgr) Get(accountId uint32, ses *Session, ctx context.Context, bh BackgroundExec) (*SystemVariables, error) {
 	sysVarsMp, err := ses.getGlobalSysVars(ctx, bh)
@@ -979,6 +991,7 @@ func (m *GlobalSysVarsMgr) Get(accountId uint32, ses *Session, ctx context.Conte
 
 	CNServiceConfig := getPu(ses.service).SV
 	useTomlConfigOverOtherConfigs(CNServiceConfig, sysVarsMp)
+	sysVarsMp["server_id"] = resolveServerID(ses)
 
 	m.Lock()
 	defer m.Unlock()
@@ -1069,6 +1082,14 @@ var gSysVarsDefs = map[string]SystemVariable{
 		Type:              InitSystemVariableStringType("version_comment"),
 		Default:           "MatrixOne",
 	},
+	"server_id": {
+		Name:              "server_id",
+		Scope:             ScopeGlobal,
+		Dynamic:           false,
+		SetVarHintApplies: false,
+		Type:              InitSystemVariableStringType("server_id"),
+		Default:           "",
+	},
 	"tx_isolation": {
 		Name:              "tx_isolation",
 		Scope:             ScopeBoth,

test/distributed/cases/system_variable/system_variables.result

@@ -6,6 +6,12 @@ set max_allowed_packet = default;
 set wait_timeout = default;
 set tx_isolation = default;
 set tx_isolation = default;
+show variables like 'server_id';
+Variable_name    Value
+server_id    uuid
+select @@server_id;
+@@server_id
+uuid
 show variables like 'auto%';
 Variable_name    Value
 auto_generate_certs    on

test/distributed/cases/system_variable/system_variables.sql

@@ -11,6 +11,10 @@ set max_allowed_packet = default;
 set wait_timeout = default;
 set tx_isolation = default;
 set tx_isolation = default;
+-- @ignore:1
+show variables like 'server_id';
+-- @ignore:0
+select @@server_id;
 
 
 -- auto_increment_increment