routing: improve dual and left joins

go.mod

@@ -25,7 +25,6 @@ require (
 	github.com/golang/mock v1.3.1
 	github.com/golang/protobuf v1.3.2
 	github.com/golang/snappy v0.0.0-20170215233205-553a64147049
-	github.com/google/btree v1.0.0 // indirect
 	github.com/google/shlex v0.0.0-20181106134648-c34317bd91bf // indirect
 	github.com/gorilla/websocket v0.0.0-20160912153041-2d1e4548da23
 	github.com/grpc-ecosystem/go-grpc-middleware v1.1.0
@@ -50,8 +49,6 @@ require (
 	github.com/minio/minio-go v0.0.0-20190131015406-c8a261de75c1
 	github.com/mitchellh/go-testing-interface v1.0.0 // indirect
 	github.com/mitchellh/mapstructure v1.1.2 // indirect
-	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
-	github.com/modern-go/reflect2 v1.0.1 // indirect
 	github.com/olekukonko/tablewriter v0.0.0-20160115111002-cca8bbc07984
 	github.com/opentracing-contrib/go-grpc v0.0.0-20180928155321-4b5a12d3ff02
 	github.com/opentracing/opentracing-go v1.1.0

go/vt/vtgate/planbuilder/route_option.go

@@ -87,12 +87,8 @@ func (ro *routeOption) JoinCanMerge(pb *primitiveBuilder, rro *routeOption, ajoi
 }
 
 func (ro *routeOption) MergeJoin(rro *routeOption, isLeftJoin bool) {
+	ro.merge(rro)
 	ro.vschemaTable = nil
-	ro.substitutions = append(ro.substitutions, rro.substitutions...)
-	if isLeftJoin {
-		return
-	}
-	// Add RHS vindexes only if it's not a left join.
 	for c, v := range rro.vindexMap {
 		if ro.vindexMap == nil {
 			ro.vindexMap = make(map[*column]vindexes.SingleColumn)
@@ -101,6 +97,16 @@ func (ro *routeOption) MergeJoin(rro *routeOption, isLeftJoin bool) {
 	}
 }
 
+// merge merges two routeOptions. If the LHS (ro) is a SelectReference,
+// then the RHS option values supersede LHS.
+func (ro *routeOption) merge(rro *routeOption) {
+	if ro.eroute.Opcode == engine.SelectReference {
+		// Swap the values and then merge.
+		*ro, *rro = *rro, *ro
+	}
+	ro.substitutions = append(ro.substitutions, rro.substitutions...)
+}
+
 func (ro *routeOption) SubqueryCanMerge(pb *primitiveBuilder, inner *routeOption) bool {
 	return ro.canMerge(inner, func() bool {
 		switch vals := inner.condition.(type) {
@@ -114,16 +120,16 @@ func (ro *routeOption) SubqueryCanMerge(pb *primitiveBuilder, inner *routeOption
 }
 
 func (ro *routeOption) MergeSubquery(subqueryOption *routeOption) {
-	ro.substitutions = append(ro.substitutions, subqueryOption.substitutions...)
+	ro.merge(subqueryOption)
 }
 
 func (ro *routeOption) UnionCanMerge(rro *routeOption) bool {
 	return ro.canMerge(rro, func() bool { return false })
 }
 
 func (ro *routeOption) MergeUnion(rro *routeOption) {
+	ro.merge(rro)
 	ro.vschemaTable = nil
-	ro.substitutions = append(ro.substitutions, rro.substitutions...)
 }
 
 func (ro *routeOption) SubqueryToTable(rb *route, vindexMap map[*column]vindexes.SingleColumn) {
@@ -149,9 +155,7 @@ func (ro *routeOption) canMerge(rro *routeOption, customCheck func() bool) bool
 			return true
 		}
 	case engine.SelectReference:
-		// TODO(sougou): this can be changed to true, but we'll have
-		// to merge against rro insteal of ro.
-		return false
+		return true
 	case engine.SelectNext:
 		return false
 	}

go/vt/vtgate/planbuilder/testdata/filter_cases.txt

@@ -233,13 +233,17 @@
 {
   "Original": "select user_extra.id from user left join user_extra on user.id = user_extra.user_id where user_extra.user_id = 5",
   "Instructions": {
-    "Opcode": "SelectScatter",
+    "Opcode": "SelectEqualUnique",
     "Keyspace": {
       "Name": "user",
       "Sharded": true
     },
     "Query": "select user_extra.id from user left join user_extra on user.id = user_extra.user_id where user_extra.user_id = 5",
     "FieldQuery": "select user_extra.id from user left join user_extra on user.id = user_extra.user_id where 1 != 1",
+    "Vindex": "user_index",
+    "Values": [
+      5
+    ],
     "Table": "user"
   }
 }

go/vt/vtgate/planbuilder/testdata/from_cases.txt

@@ -927,35 +927,19 @@
   }
 }
 
-# reference table doesn't merge with other opcodes yet.
+# reference table can merge with other opcodes left to right.
 "select ref.col from ref join user"
 {
   "Original": "select ref.col from ref join user",
   "Instructions": {
-    "Opcode": "Join",
-    "Left": {
-      "Opcode": "SelectReference",
-      "Keyspace": {
-        "Name": "user",
-        "Sharded": true
-      },
-      "Query": "select ref.col from ref",
-      "FieldQuery": "select ref.col from ref where 1 != 1",
-      "Table": "ref"
-    },
-    "Right": {
-      "Opcode": "SelectScatter",
-      "Keyspace": {
-        "Name": "user",
-        "Sharded": true
-      },
-      "Query": "select 1 from user",
-      "FieldQuery": "select 1 from user where 1 != 1",
-      "Table": "user"
+    "Opcode": "SelectScatter",
+    "Keyspace": {
+      "Name": "user",
+      "Sharded": true
     },
-    "Cols": [
-      -1
-    ]
+    "Query": "select ref.col from ref join user",
+    "FieldQuery": "select ref.col from ref join user where 1 != 1",
+    "Table": "user"
   }
 }
 

go/vt/vtgate/planbuilder/testdata/unsupported_cases.txt

@@ -432,8 +432,3 @@
 
 "select func(keyspace_id) from user_index where id = :id"
 "unsupported: expression on results of a vindex function"
-
-# Multi-table unique vindex constraint on left table of left join, two levels of join, simple aggregation
-# This should work, but doesn't. See https://github.com/vitessio/vitess/issues/4772
-"select user.id, count(*) from user left join user_extra ue1 on user.id = ue1.user_id left join user_extra ue2 on ue1.user_id = ue2.user_id group by user.id"
-"unsupported: cross-shard query with aggregates"