report SQLState in MySQLError

to allow library users to distinguish user-defined from client / server errors

errors.go

@@ -56,11 +56,15 @@ func SetLogger(logger Logger) error {
 
 // MySQLError is an error type which represents a single MySQL error
 type MySQLError struct {
-	Number  uint16
-	Message string
+	Number   uint16
+	SQLState string
+	Message  string
 }
 
 func (me *MySQLError) Error() string {
+	if me.SQLState != "" {
+		return fmt.Sprintf("Error %d (%s): %s", me.Number, me.SQLState, me.Message)
+	}
 	return fmt.Sprintf("Error %d: %s", me.Number, me.Message)
 }
 
@@ -70,3 +74,10 @@ func (me *MySQLError) Is(err error) bool {
 	}
 	return false
 }
+
+func (me *MySQLError) IsWithSQLState(err error) bool {
+	if merr, ok := err.(*MySQLError); ok {
+		return merr.Number == me.Number && merr.SQLState == me.SQLState
+	}
+	return false
+}

errors_test.go

@@ -43,13 +43,13 @@ func TestErrorsStrictIgnoreNotes(t *testing.T) {
 }
 
 func TestMySQLErrIs(t *testing.T) {
-	infraErr := &MySQLError{1234, "the server is on fire"}
-	otherInfraErr := &MySQLError{1234, "the datacenter is flooded"}
+	infraErr := &MySQLError{1234, "", "the server is on fire"}
+	otherInfraErr := &MySQLError{1234, "", "the datacenter is flooded"}
 	if !errors.Is(infraErr, otherInfraErr) {
 		t.Errorf("expected errors to be the same: %+v %+v", infraErr, otherInfraErr)
 	}
 
-	differentCodeErr := &MySQLError{5678, "the server is on fire"}
+	differentCodeErr := &MySQLError{5678, "", "the server is on fire"}
 	if errors.Is(infraErr, differentCodeErr) {
 		t.Fatalf("expected errors to be different: %+v %+v", infraErr, differentCodeErr)
 	}
@@ -59,3 +59,16 @@ func TestMySQLErrIs(t *testing.T) {
 		t.Fatalf("expected errors to be different: %+v %+v", infraErr, nonMysqlErr)
 	}
 }
+
+func TestMySQLErrIsWithSQLState(t *testing.T) {
+	infraErr := &MySQLError{1234, "HY000", "the server is on fire"}
+	otherInfraErr := &MySQLError{1234, "HY000", "the datacenter is flooded"}
+	if !infraErr.IsWithSQLState(otherInfraErr) {
+		t.Errorf("expected errors to be the same: %+v %+v", infraErr, otherInfraErr)
+	}
+
+	differentCodeErr := &MySQLError{1234, "42000", "the server is on fire"}
+	if infraErr.IsWithSQLState(differentCodeErr) {
+		t.Fatalf("expected errors to be different: %+v %+v", infraErr, differentCodeErr)
+	}
+}