allow SYSTEM as valid time zone

Author: angelamayxie

enginetest/queries/time_queries.go

@@ -80,4 +80,22 @@ var TimeQueryTests = []ScriptTest{
 			},
 		},
 	},
+	{
+		Name:        "set timezone to SYSTEM",
+		SetUpScript: []string{},
+		Assertions: []ScriptTestAssertion{
+			{
+				Query:    "select @@time_zone",
+				Expected: []sql.Row{{"SYSTEM"}},
+			},
+			{
+				Query:    "set @old_time_zone=@@time_zone",
+				Expected: []sql.Row{{types.NewOkResult(0)}},
+			},
+			{
+				Query:    "set @@time_zone=@old_time_zone",
+				Expected: []sql.Row{{types.NewOkResult(0)}},
+			},
+		},
+	},
 }

sql/rowexec/rel_iters.go

@@ -16,10 +16,6 @@ package rowexec
 
 import (
 	"errors"
-	"io"
-	"strings"
-	"time"
-
 	"github.com/dolthub/go-mysql-server/sql"
 	"github.com/dolthub/go-mysql-server/sql/expression"
 	"github.com/dolthub/go-mysql-server/sql/expression/function/aggregation"
@@ -28,6 +24,8 @@ import (
 	"github.com/dolthub/go-mysql-server/sql/plan"
 	"github.com/dolthub/go-mysql-server/sql/transform"
 	"github.com/dolthub/go-mysql-server/sql/types"
+	"io"
+	"strings"
 )
 
 // windowToIter transforms a plan.Window into a series
@@ -476,11 +474,7 @@ func validateSystemVariableValue(sysVarName string, val interface{}) error {
 		if !ok {
 			return sql.ErrInvalidTimeZone.New(val)
 		}
-		_, err := time.LoadLocation(valStr)
-		if err == nil {
-			return nil
-		}
-		if !sql.ValidTimeOffset(valStr) {
+		if !sql.ValidTimeZone(valStr) {
 			return sql.ErrInvalidTimeZone.New(valStr)
 		}
 	}

sql/time.go

@@ -19,6 +19,7 @@ import (
 	"fmt"
 	"math"
 	"regexp"
+	"strings"
 	"time"
 )
 
@@ -47,8 +48,12 @@ func ConvertTimeZone(datetime time.Time, fromLocation string, toLocation string)
 	return datetime.Add(delta), true
 }
 
-func ValidTimeOffset(str string) bool {
-	return offsetRegex.MatchString(str)
+func ValidTimeZone(str string) bool {
+	_, err := time.LoadLocation(str)
+	if err == nil {
+		return true
+	}
+	return offsetRegex.MatchString(str) || strings.ToUpper(str) == "SYSTEM"
 }
 
 // MySQLOffsetToDuration takes in a MySQL timezone offset (e.g. "+01:00") and returns it as a time.Duration.