add a flag to indicate if a vindex handles null value

go/test/endtoend/vtgate/main_test.go

@@ -100,6 +100,20 @@ create table t5_null_vindex(
 	id bigint not null,
 	idx varchar(50),
 	primary key(id)
+) Engine=InnoDB;
+
+create table t6(
+	id1 bigint,
+	id2 varchar(10),
+	primary key(id1)
+) Engine=InnoDB;
+
+create table t6_id2_idx(
+	id2 varchar(10),
+	id1 bigint,
+	keyspace_id varbinary(50),
+	primary key(id1),
+	key(id2)
 ) Engine=InnoDB;`
 
 	VSchema = `
@@ -151,6 +165,16 @@ create table t5_null_vindex(
         "to": "keyspace_id"
       },
       "owner": "t4"
+    },
+    "t6_id2_vdx": {
+      "type": "consistent_lookup",
+      "params": {
+        "table": "t6_id2_idx",
+        "from": "id2,id1",
+        "to": "keyspace_id",
+        "ignore_nulls": "true"
+      },
+      "owner": "t6"
     }
   },
   "tables": {
@@ -233,6 +257,26 @@ create table t5_null_vindex(
           "name": "unicode_loose_md5"
         }
       ]
+    },
+	"t6": {
+      "column_vindexes": [
+        {
+          "column": "id1",
+          "name": "hash"
+        },
+        {
+          "columns": ["id2", "id1"],
+          "name": "t6_id2_vdx"
+        }
+      ]
+    },
+    "t6_id2_idx": {
+      "column_vindexes": [
+        {
+          "column": "id2",
+          "name": "xxhash"
+        }
+      ]
     },
 	"t5_null_vindex": {
       "column_vindexes": [

go/test/endtoend/vtgate/misc_test.go

@@ -509,6 +509,28 @@ func TestConsistentLookupUpdate(t *testing.T) {
 	require.Empty(t, qr.Rows)
 }
 
+func TestSelectNullLookup(t *testing.T) {
+	ctx := context.Background()
+	conn, err := mysql.Connect(ctx, &vtParams)
+	require.NoError(t, err)
+	defer conn.Close()
+
+	exec(t, conn, "begin")
+	exec(t, conn, "insert into t6(id1, id2) values(1, 'a'), (2, 'b'), (3, null)")
+	exec(t, conn, "commit")
+
+	assertMatches(t, conn, "select id1, id2 from t6 order by id1", "[[INT64(1) VARCHAR(\"a\")] [INT64(2) VARCHAR(\"b\")] [INT64(3) NULL]]")
+	assertIsEmpty(t, conn, "select id1, id2 from t6 where id2 = null")
+	assertMatches(t, conn, "select id1, id2 from t6 where id2 is null", "[[INT64(3) NULL]]")
+	assertMatches(t, conn, "select id1, id2 from t6 where id2 is not null order by id1", "[[INT64(1) VARCHAR(\"a\")] [INT64(2) VARCHAR(\"b\")]]")
+	assertIsEmpty(t, conn, "select id1, id2 from t6 where id1 IN (null)")
+	assertMatches(t, conn, "select id1, id2 from t6 where id1 IN (1,2,null) order by id1", "[[INT64(1) VARCHAR(\"a\")] [INT64(2) VARCHAR(\"b\")]]")
+	assertIsEmpty(t, conn, "select id1, id2 from t6 where id1 NOT IN (1,null) order by id1")
+	assertMatches(t, conn, "select id1, id2 from t6 where id1 NOT IN (1,3)", "[[INT64(2) VARCHAR(\"b\")]]")
+
+	exec(t, conn, "delete from t6")
+}
+
 func TestSelectNull(t *testing.T) {
 	ctx := context.Background()
 	conn, err := mysql.Connect(ctx, &vtParams)

go/vt/vtgate/planbuilder/route_option.go

@@ -301,6 +301,7 @@ func (ro *routeOption) computeISPlan(pb *primitiveBuilder, comparison *sqlparser
 	}
 
 	vindex = ro.FindVindex(pb, comparison.Expr)
+	// fallback to scatter gather if there is no vindex
 	if vindex == nil {
 		return engine.SelectScatter, nil, nil
 	}

go/vt/vtgate/vindexes/consistent_lookup.go

@@ -91,6 +91,14 @@ func (lu *ConsistentLookup) Map(vcursor VCursor, ids []sqltypes.Value) ([]key.De
 		return out, nil
 	}
 
+	// if ignore_nulls is set and the query is about single null value, then fallback to all shards
+	if len(ids) == 1 && ids[0].IsNull() && lu.lkp.IgnoreNulls {
+		for range ids {
+			out = append(out, key.DestinationKeyRange{KeyRange: &topodatapb.KeyRange{}})
+		}
+		return out, nil
+	}
+
 	results, err := lu.lkp.Lookup(vcursor, ids)
 	if err != nil {
 		return nil, err

go/vt/vtgate/vindexes/lookup.go

@@ -76,6 +76,14 @@ func (ln *LookupNonUnique) Map(vcursor VCursor, ids []sqltypes.Value) ([]key.Des
 		return out, nil
 	}
 
+	// if ignore_nulls is set and the query is about single null value, then fallback to all shards
+	if len(ids) == 1 && ids[0].IsNull() && ln.lkp.IgnoreNulls {
+		for range ids {
+			out = append(out, key.DestinationKeyRange{KeyRange: &topodatapb.KeyRange{}})
+		}
+		return out, nil
+	}
+
 	results, err := ln.lkp.Lookup(vcursor, ids)
 	if err != nil {
 		return nil, err

go/vt/vtgate/vindexes/lookup_hash.go

@@ -110,6 +110,14 @@ func (lh *LookupHash) Map(vcursor VCursor, ids []sqltypes.Value) ([]key.Destinat
 		return out, nil
 	}
 
+	// if ignore_nulls is set and the query is about single null value, then fallback to all shards
+	if len(ids) == 1 && ids[0].IsNull() && lh.lkp.IgnoreNulls {
+		for range ids {
+			out = append(out, key.DestinationKeyRange{KeyRange: &topodatapb.KeyRange{}})
+		}
+		return out, nil
+	}
+
 	results, err := lh.lkp.Lookup(vcursor, ids)
 	if err != nil {
 		return nil, err

go/vt/vtgate/vindexes/lookup_unicodeloosemd5_hash.go

@@ -111,6 +111,14 @@ func (lh *LookupUnicodeLooseMD5Hash) Map(vcursor VCursor, ids []sqltypes.Value)
 		return out, nil
 	}
 
+	// if ignore_nulls is set and the query is about single null value, then fallback to all shards
+	if len(ids) == 1 && ids[0].IsNull() && lh.lkp.IgnoreNulls {
+		for range ids {
+			out = append(out, key.DestinationKeyRange{KeyRange: &topodatapb.KeyRange{}})
+		}
+		return out, nil
+	}
+
 	ids, err := convertIds(ids)
 	if err != nil {
 		return nil, err