Don't rewrite enum columns when not necessary.

go/libraries/doltcore/schema/typeinfo/typeinfo.go

@@ -134,6 +134,17 @@ type TypeInfo interface {
 	fmt.Stringer
 }
 
+// RequiresRewrite returns whether or now changing a column type from |old| to |new| requires rewriting table rows.
+func RequiresRewrite(old TypeInfo, new TypeInfo) bool {
+	oldEnum, isOldEnum := old.ToSqlType().(sql.EnumType)
+	newEnum, isNewEnum := new.ToSqlType().(sql.EnumType)
+	if isOldEnum && isNewEnum && oldEnum.IsSubsetOf(newEnum) {
+		return false
+	}
+
+	return true
+}
+
 // FromSqlType takes in a sql.Type and returns the most relevant TypeInfo.
 func FromSqlType(sqlType sql.Type) (TypeInfo, error) {
 	if gmsExtendedType, ok := sqlType.(gmstypes.ExtendedType); ok {

go/libraries/doltcore/sqle/tables.go

@@ -1682,7 +1682,7 @@ func (t *AlterableDoltTable) isIncompatibleTypeChange(oldColumn *sql.Column, new
 	if !existingCol.TypeInfo.Equals(newCol.TypeInfo) {
 		if types.IsFormat_DOLT(t.Format()) {
 			// This is overly broad, we could narrow this down a bit
-			return true
+			return typeinfo.RequiresRewrite(existingCol.TypeInfo, newCol.TypeInfo)
 		}
 		if existingCol.Kind != newCol.Kind {
 			return true