From 23d7c4f87e7941ad648266ce6fe7f50f0359d834 Mon Sep 17 00:00:00 2001
From: Harshit Gangal <harshit@planetscale.com>
Date: Tue, 19 Oct 2021 01:23:38 +0530
Subject: [PATCH] handle sql_mode differently for new value change validation

Signed-off-by: Harshit Gangal <harshit@planetscale.com>
---
 go/vt/vtgate/engine/set.go | 66 ++++++++++++++++++++++++++++++++++----
 1 file changed, 60 insertions(+), 6 deletions(-)

diff --git a/go/vt/vtgate/engine/set.go b/go/vt/vtgate/engine/set.go
index 53d8fe024de..2b5cdc5ad69 100644
--- a/go/vt/vtgate/engine/set.go
+++ b/go/vt/vtgate/engine/set.go
@@ -327,6 +327,9 @@ func (svs *SysVarReservedConn) execSetStatement(vcursor VCursor, rss []*srvtopo.
 
 func (svs *SysVarReservedConn) checkAndUpdateSysVar(vcursor VCursor, res evalengine.ExpressionEnv) (bool, error) {
 	sysVarExprValidationQuery := fmt.Sprintf("select %s from dual where @@%s != %s", svs.Expr, svs.Name, svs.Expr)
+	if svs.Name == "sql_mode" {
+		sysVarExprValidationQuery = fmt.Sprintf("select @@%s orig, %s new", svs.Name, svs.Expr)
+	}
 	rss, _, err := vcursor.ResolveDestinations(svs.Keyspace.Name, nil, []key.Destination{key.DestinationKeyspaceID{0}})
 	if err != nil {
 		return false, err
@@ -335,18 +338,69 @@ func (svs *SysVarReservedConn) checkAndUpdateSysVar(vcursor VCursor, res evaleng
 	if err != nil {
 		return false, err
 	}
-	if len(qr.Rows) == 0 {
+	changed := len(qr.Rows) > 0
+	if !changed {
 		return false, nil
 	}
-	// TODO : validate how value needs to be stored.
-	value := qr.Rows[0][0]
-	buf := new(bytes.Buffer)
-	value.EncodeSQL(buf)
-	vcursor.Session().SetSysVar(svs.Name, buf.String())
+
+	var newVal string
+	if svs.Name == "sql_mode" {
+		changed, newVal = sqlModeChangedValue(qr)
+		if !changed {
+			return false, nil
+		}
+	} else {
+		buf := new(bytes.Buffer)
+		value := qr.Rows[0][0]
+		value.EncodeSQL(buf)
+		newVal = buf.String()
+	}
+	vcursor.Session().SetSysVar(svs.Name, newVal)
 	vcursor.Session().NeedsReservedConn()
 	return true, nil
 }
 
+func sqlModeChangedValue(qr *sqltypes.Result) (bool, string) {
+	if len(qr.Fields) != 2 {
+		return false, ""
+	}
+	if len(qr.Rows[0]) != 2 {
+		return false, ""
+	}
+	orig := qr.Rows[0][0].ToString()
+	newVal := qr.Rows[0][1].ToString()
+
+	origArr := strings.Split(orig, ",")
+	// Keep track of if the value is seen or not.
+	origMap := map[string]bool{}
+	for _, oVal := range origArr {
+		// Default is not seen.
+		origMap[oVal] = true
+	}
+	uniqOrigVal := len(origMap)
+	origValSeen := 0
+
+	changed := false
+	newValArr := strings.Split(newVal, ",")
+	for _, nVal := range newValArr {
+		notSeen, exists := origMap[nVal]
+		if !exists {
+			changed = true
+			break
+		}
+		if exists && notSeen {
+			// Value seen. Turn it off
+			origMap[nVal] = false
+			origValSeen++
+		}
+	}
+	if !changed && uniqOrigVal != origValSeen {
+		changed = true
+	}
+
+	return changed, newVal
+}
+
 var _ SetOp = (*SysVarSetAware)(nil)
 
 // MarshalJSON marshals all the json