add sys var enum test

Author: elianddb

enginetest/queries/script_queries.go

@@ -9136,6 +9136,33 @@ where
 			},
 		},
 	},
+	{
+		Name:    "enum conversion with system variables",
+		Dialect: "mysql",
+		SetUpScript: []string{
+			"create table t (e enum('ON', 'OFF', 'AUTO'));",
+			"set autocommit = 'ON';",
+			"insert into t values(@@autocommit), ('OFF'), ('AUTO');",
+		},
+		Assertions: []ScriptTestAssertion{
+			{
+				Query: "select e, @@autocommit, e = @@autocommit from t order by e;",
+				Expected: []sql.Row{
+					{"ON", 1, true},
+					{"OFF", 1, false},
+					{"AUTO", 1, false},
+				},
+			},
+			{
+				Query: "select e, concat(e, @@version_comment) from t order by e;",
+				Expected: []sql.Row{
+					{"ON", "ONDolt"},
+					{"OFF", "OFFDolt"},
+					{"AUTO", "AUTODolt"},
+				},
+			},
+		},
+	},
 	{
 		Skip:    true,
 		Name:    "enums with foreign keys",

sql/types/strings.go

@@ -554,14 +554,12 @@ func ConvertToCollatedString(ctx context.Context, val interface{}, typ sql.Type)
 	} else {
 		collation = sql.Collation_Default
 		// Handle enum types in string context even without collation
-		if IsEnum(typ) {
-			if enumType, ok := typ.(sql.EnumType); ok {
-				content, err = convertEnumToString(ctx, val, enumType)
-				if err != nil {
-					return "", sql.Collation_Unspecified, err
-				}
-				return content, collation, nil
+		if enumType, ok := typ.(sql.EnumType); ok {
+			content, err = convertEnumToString(ctx, val, enumType)
+			if err != nil {
+				return "", sql.Collation_Unspecified, err
 			}
+			return content, collation, nil
 		}
 		content, err = convertToLongTextString(ctx, val)
 		if err != nil {