From 00a810940a81b335c24068a9e5831b87bfb1ddbb Mon Sep 17 00:00:00 2001
From: Andres Taylor <andres@planetscale.com>
Date: Mon, 4 May 2020 20:25:46 +0200
Subject: [PATCH] Use 'SelectNone' for all equality against null

Signed-off-by: Andres Taylor <andres@planetscale.com>
---
 go/vt/vtgate/planbuilder/route_option.go       |  8 +++++---
 .../planbuilder/testdata/filter_cases.txt      | 18 ++++++++++++++++++
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/go/vt/vtgate/planbuilder/route_option.go b/go/vt/vtgate/planbuilder/route_option.go
index e374e03ad6b..c38c163231e 100644
--- a/go/vt/vtgate/planbuilder/route_option.go
+++ b/go/vt/vtgate/planbuilder/route_option.go
@@ -269,6 +269,11 @@ func (ro *routeOption) computePlan(pb *primitiveBuilder, filter sqlparser.Expr)
 func (ro *routeOption) computeEqualPlan(pb *primitiveBuilder, comparison *sqlparser.ComparisonExpr) (opcode engine.RouteOpcode, vindex vindexes.SingleColumn, condition sqlparser.Expr) {
 	left := comparison.Left
 	right := comparison.Right
+
+	if sqlparser.IsNull(right) {
+		return engine.SelectNone, nil, nil
+	}
+
 	vindex = ro.FindVindex(pb, left)
 	if vindex == nil {
 		left, right = right, left
@@ -277,9 +282,6 @@ func (ro *routeOption) computeEqualPlan(pb *primitiveBuilder, comparison *sqlpar
 			return engine.SelectScatter, nil, nil
 		}
 	}
-	if sqlparser.IsNull(right) {
-		return engine.SelectNone, nil, nil
-	}
 	if !ro.exprIsValue(right) {
 		return engine.SelectScatter, nil, nil
 	}
diff --git a/go/vt/vtgate/planbuilder/testdata/filter_cases.txt b/go/vt/vtgate/planbuilder/testdata/filter_cases.txt
index 8bb634c68e1..74a3c7fa9a2 100644
--- a/go/vt/vtgate/planbuilder/testdata/filter_cases.txt
+++ b/go/vt/vtgate/planbuilder/testdata/filter_cases.txt
@@ -16,6 +16,24 @@
   }
 }
 
+# Query that always return empty
+"select id from user where someColumn = null"
+{
+  "QueryType": "SELECT",
+  "Original": "select id from user where someColumn = null",
+  "Instructions": {
+    "OperatorType": "Route",
+    "Variant": "SelectNone",
+    "Keyspace": {
+      "Name": "user",
+      "Sharded": true
+    },
+    "FieldQuery": "select id from user where 1 != 1",
+    "Query": "select id from user where someColumn = null",
+    "Table": "user"
+  }
+}
+
 # Single table unique vindex route
 "select id from user where user.id = 5"
 {