fix builder grow

Author: lqs

common.go

@@ -95,7 +95,9 @@ func commaTables(scope scope, tables []Table) string {
 }
 
 func commaValuesBuilder(scope scope, builder *strings.Builder, values []interface{}) error {
-	builder.Grow(16 * (len(values) + 2)) // hopefully reduce copying
+	if len(values) == 0 {
+		return nil
+	}
 	for i, item := range values {
 		if i > 0 {
 			builder.WriteString(", ")

insert.go

@@ -158,11 +158,11 @@ func (s insertStatus) GetSQL() (string, error) {
 				if i > 0 {
 					valuesBuilder.WriteString(", ")
 				}
-				valuesBuilder.WriteString("(")
+				valuesBuilder.WriteByte('(')
 				if err := commaValuesBuilder(s.scope, &valuesBuilder, model.GetValues()); err != nil {
 					return "", err
 				}
-				valuesBuilder.WriteString(")")
+				valuesBuilder.WriteByte(')')
 			}
 		}
 	} else {