fix and test

enginetest/queries/variable_queries.go

@@ -338,6 +338,16 @@ var VariableQueries = []ScriptTest{
 			{"ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION,NO_ZERO_DATE,NO_ZERO_IN_DATE,STRICT_ALL_TABLES,STRICT_TRANS_TABLES,TRADITIONAL"},
 		},
 	},
+	{
+		Name: "set sql_mode variable ignores empty strings",
+		SetUpScript: []string{
+			`SET sql_mode = ',,,,STRICT_TRANS_TABLES,,,,,NO_AUTO_VALUE_ON_ZERO,,,,NO_ENGINE_SUBSTITUTION,,,,,,'`,
+		},
+		Query: "SELECT @@sql_mode",
+		Expected: []sql.Row{
+			{"NO_AUTO_VALUE_ON_ZERO,NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES"},
+		},
+	},
 	{
 		Name: "show variables renders enums after set",
 		SetUpScript: []string{

sql/types/set.go

@@ -368,6 +368,10 @@ func (t SetType) convertStringToBitField(str string) (uint64, error) {
 	var bitField uint64
 	vals := strings.Split(str, ",")
 	for _, val := range vals {
+		// empty string should hash to 0, so just skip
+		if val == "" {
+			continue
+		}
 		compareVal := val
 		if t.collation != sql.Collation_binary {
 			compareVal = strings.TrimRight(compareVal, " ")