sessionctx: Set foreign_key_checks = OFF

expression/integration_test.go

@@ -3693,6 +3693,14 @@ func (s *testIntegrationSuite) TestValuesInNonInsertStmt(c *C) {
 	res.Check(testkit.Rows(`<nil> <nil> <nil> <nil> <nil> <nil> <nil>`))
 }
 
+func (s *testIntegrationSuite) TestForeignKeyVar(c *C) {
+
+	tk := testkit.NewTestKit(c, s.store)
+
+	tk.MustExec("SET FOREIGN_KEY_CHECKS=1")
+	tk.MustQuery("SHOW WARNINGS").Check(testkit.Rows("Warning 1105 variable 'foreign_key_checks' does not yet support value: 1"))
+}
+
 func (s *testIntegrationSuite) TestUserVarMockWindFunc(c *C) {
 	tk := testkit.NewTestKit(c, s.store)
 	tk.MustExec(`use test;`)

sessionctx/variable/sysvar.go

@@ -71,14 +71,15 @@ const (
 
 // Variable errors
 var (
-	UnknownStatusVar       = terror.ClassVariable.New(CodeUnknownStatusVar, "unknown status variable")
-	UnknownSystemVar       = terror.ClassVariable.New(CodeUnknownSystemVar, mysql.MySQLErrName[mysql.ErrUnknownSystemVariable])
-	ErrIncorrectScope      = terror.ClassVariable.New(CodeIncorrectScope, mysql.MySQLErrName[mysql.ErrIncorrectGlobalLocalVar])
-	ErrUnknownTimeZone     = terror.ClassVariable.New(CodeUnknownTimeZone, mysql.MySQLErrName[mysql.ErrUnknownTimeZone])
-	ErrReadOnly            = terror.ClassVariable.New(CodeReadOnly, "variable is read only")
-	ErrWrongValueForVar    = terror.ClassVariable.New(CodeWrongValueForVar, mysql.MySQLErrName[mysql.ErrWrongValueForVar])
-	ErrWrongTypeForVar     = terror.ClassVariable.New(CodeWrongTypeForVar, mysql.MySQLErrName[mysql.ErrWrongTypeForVar])
-	ErrTruncatedWrongValue = terror.ClassVariable.New(CodeTruncatedWrongValue, mysql.MySQLErrName[mysql.ErrTruncatedWrongValue])
+	UnknownStatusVar          = terror.ClassVariable.New(CodeUnknownStatusVar, "unknown status variable")
+	UnknownSystemVar          = terror.ClassVariable.New(CodeUnknownSystemVar, mysql.MySQLErrName[mysql.ErrUnknownSystemVariable])
+	ErrIncorrectScope         = terror.ClassVariable.New(CodeIncorrectScope, mysql.MySQLErrName[mysql.ErrIncorrectGlobalLocalVar])
+	ErrUnknownTimeZone        = terror.ClassVariable.New(CodeUnknownTimeZone, mysql.MySQLErrName[mysql.ErrUnknownTimeZone])
+	ErrReadOnly               = terror.ClassVariable.New(CodeReadOnly, "variable is read only")
+	ErrWrongValueForVar       = terror.ClassVariable.New(CodeWrongValueForVar, mysql.MySQLErrName[mysql.ErrWrongValueForVar])
+	ErrWrongTypeForVar        = terror.ClassVariable.New(CodeWrongTypeForVar, mysql.MySQLErrName[mysql.ErrWrongTypeForVar])
+	ErrTruncatedWrongValue    = terror.ClassVariable.New(CodeTruncatedWrongValue, mysql.MySQLErrName[mysql.ErrTruncatedWrongValue])
+	ErrUnsupportedValueForVar = terror.ClassVariable.New(CodeUnknownStatusVar, "variable '%s' does not yet support value: %s")
 )
 
 func init() {
@@ -221,7 +222,7 @@ var defaultSysVars = []*SysVar{
 	{ScopeNone, "innodb_autoinc_lock_mode", "1"},
 	{ScopeGlobal, "slave_net_timeout", "3600"},
 	{ScopeGlobal, "key_buffer_size", "8388608"},
-	{ScopeGlobal | ScopeSession, ForeignKeyChecks, "1"},
+	{ScopeGlobal | ScopeSession, ForeignKeyChecks, "OFF"},
 	{ScopeGlobal, "host_cache_size", "279"},
 	{ScopeGlobal, DelayKeyWrite, "ON"},
 	{ScopeNone, "metadata_locks_cache_size", "1024"},

sessionctx/variable/varsutil.go

@@ -236,6 +236,16 @@ func ValidateSetSystemVar(vars *SessionVars, name string, value string) (string,
 		return value, ErrWrongValueForVar.GenWithStackByArgs(name, value)
 	case FlushTime:
 		return checkUInt64SystemVar(name, value, 0, secondsPerYear, vars)
+	case ForeignKeyChecks:
+		if strings.EqualFold(value, "ON") || value == "1" {
+			// TiDB does not yet support foreign keys.
+			// For now, resist the change and show a warning.
+			vars.StmtCtx.AppendWarning(ErrUnsupportedValueForVar.GenWithStackByArgs(name, value))
+			return "OFF", nil
+		} else if strings.EqualFold(value, "OFF") || value == "0" {
+			return "OFF", nil
+		}
+		return value, ErrWrongValueForVar.GenWithStackByArgs(name, value)
 	case GroupConcatMaxLen:
 		// The reasonable range of 'group_concat_max_len' is 4~18446744073709551615(64-bit platforms)
 		// See https://dev.mysql.com/doc/refman/8.0/en/server-system-variables.html#sysvar_group_concat_max_len for details
@@ -288,7 +298,7 @@ func ValidateSetSystemVar(vars *SessionVars, name string, value string) (string,
 	case WarningCount, ErrorCount:
 		return value, ErrReadOnly.GenWithStackByArgs(name)
 	case GeneralLog, TiDBGeneralLog, AvoidTemporalUpgrade, BigTables, CheckProxyUsers, CoreFile, EndMakersInJSON, SQLLogBin, OfflineMode,
-		PseudoSlaveMode, LowPriorityUpdates, SkipNameResolve, ForeignKeyChecks, SQLSafeUpdates, TiDBConstraintCheckInPlace:
+		PseudoSlaveMode, LowPriorityUpdates, SkipNameResolve, SQLSafeUpdates, TiDBConstraintCheckInPlace:
 		if strings.EqualFold(value, "ON") || value == "1" {
 			return "1", nil
 		} else if strings.EqualFold(value, "OFF") || value == "0" {

sessionctx/variable/varsutil_test.go

@@ -103,6 +103,16 @@ func (s *testVarsutilSuite) TestVarsutil(c *C) {
 	c.Assert(val, Equals, "1")
 	c.Assert(SetSessionSystemVar(v, "autocommit", types.Datum{}), NotNil)
 
+	// 0 converts to OFF
+	SetSessionSystemVar(v, "foreign_key_checks", types.NewStringDatum("0"))
+	val, err = GetSessionSystemVar(v, "foreign_key_checks")
+	c.Assert(val, Equals, "OFF")
+
+	// 1/ON is not supported (generates a warning and sets to OFF)
+	SetSessionSystemVar(v, "foreign_key_checks", types.NewStringDatum("1"))
+	val, err = GetSessionSystemVar(v, "foreign_key_checks")
+	c.Assert(val, Equals, "OFF")
+
 	SetSessionSystemVar(v, "sql_mode", types.NewStringDatum("strict_trans_tables"))
 	val, err = GetSessionSystemVar(v, "sql_mode")
 	c.Assert(err, IsNil)