Default sql mode for common path (#2520)

* Default sql mode for common path

* jason comments

* upper case

sql/sql_mode.go

@@ -30,8 +30,24 @@ const (
 	NoAutoValueOnZero    = "NO_AUTO_VALUE_ON_ZERO"
 	NoEngineSubstitution = "NO_ENGINE_SUBSTITUTION"
 	StrictTransTables    = "STRICT_TRANS_TABLES"
+	DefaultSqlMode       = "NO_ENGINE_SUBSTITUTION,ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES"
 )
 
+var defaultMode *SqlMode
+
+func init() {
+	elements := strings.Split(strings.ToLower(DefaultSqlMode), ",")
+	sort.Strings(elements)
+	modes := map[string]struct{}{}
+	for _, element := range elements {
+		modes[element] = struct{}{}
+	}
+	defaultMode = &SqlMode{
+		modes:      modes,
+		modeString: DefaultSqlMode,
+	}
+}
+
 // SqlMode encodes the SQL mode string and provides methods for querying the enabled modes.
 type SqlMode struct {
 	modes      map[string]struct{}
@@ -59,6 +75,9 @@ func LoadSqlMode(ctx *Context) *SqlMode {
 // NewSqlModeFromString returns a new SqlMode instance, constructed from the specified |sqlModeString| that
 // has a comma delimited list of SQL modes (e.g. "ONLY_FULLY_GROUP_BY,ANSI_QUOTES").
 func NewSqlModeFromString(sqlModeString string) *SqlMode {
+	if strings.EqualFold(sqlModeString, DefaultSqlMode) {
+		return defaultMode
+	}
 	sqlModeString = strings.ToLower(sqlModeString)
 	elements := strings.Split(sqlModeString, ",")
 	sort.Strings(elements)

sql/variables/system_variables.go

@@ -2407,7 +2407,7 @@ var systemVars = map[string]sql.SystemVariable{
 		Dynamic:           true,
 		SetVarHintApplies: true,
 		Type:              types.NewSystemSetType("sql_mode", "ALLOW_INVALID_DATES", "ANSI_QUOTES", "ERROR_FOR_DIVISION_BY_ZERO", "HIGH_NOT_PRECEDENCE", "IGNORE_SPACE", "NO_AUTO_VALUE_ON_ZERO", "NO_BACKSLASH_ESCAPES", "NO_DIR_IN_CREATE", "NO_ENGINE_SUBSTITUTION", "NO_UNSIGNED_SUBTRACTION", "NO_ZERO_DATE", "NO_ZERO_IN_DATE", "ONLY_FULL_GROUP_BY", "PAD_CHAR_TO_FULL_LENGTH", "PIPES_AS_CONCAT", "REAL_AS_FLOAT", "STRICT_ALL_TABLES", "STRICT_TRANS_TABLES", "TIME_TRUNCATE_FRACTIONAL", "TRADITIONAL", "ANSI"),
-		Default:           "NO_ENGINE_SUBSTITUTION,ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES",
+		Default:           sql.DefaultSqlMode,
 	},
 	"sql_notes": &sql.MysqlSystemVariable{
 		Name:              "sql_notes",