[release-19.0] bugfix: don't treat join predicates as filter predicat…

…es (#16472) (#16474)

Signed-off-by: Andres Taylor <andres@planetscale.com>
Co-authored-by: Andrés Taylor <andres@planetscale.com>

go/test/endtoend/vtgate/queries/misc/misc_test.go

@@ -319,6 +319,17 @@ func TestTransactionModeVar(t *testing.T) {
 	}
 }
 
+// TestAliasesInOuterJoinQueries tests that aliases work in queries that have outer join clauses.
+func TestAliasesInOuterJoinQueries(t *testing.T) {
+	mcmp, closer := start(t)
+	defer closer()
+
+	// Insert data into the 2 tables
+	mcmp.Exec("insert into t1(id1, id2) values (1,2), (42,5), (5, 42)")
+	mcmp.Exec("insert into tbl(id, unq_col, nonunq_col) values (1,2,3), (2,5,3), (3, 42, 2)")
+	mcmp.ExecWithColumnCompare("select * from t1 t left join tbl on t.id1 = 666 and t.id2 = tbl.id")
+}
+
 func TestAlterTableWithView(t *testing.T) {
 	mcmp, closer := start(t)
 	defer closer()

go/vt/vtgate/planbuilder/operators/apply_join.go

@@ -277,6 +277,10 @@ func (aj *ApplyJoin) ShortDescription() string {
 	}
 
 	firstPart := fmt.Sprintf("on %s columns: %s", fn(aj.JoinPredicates), fn(aj.JoinColumns))
+	if aj.LeftJoin {
+		firstPart = "LEFT JOIN " + firstPart
+	}
+
 	if len(aj.ExtraLHSVars) == 0 {
 		return firstPart
 	}

go/vt/vtgate/planbuilder/operators/route_planning.go

@@ -358,13 +358,18 @@ func mergeOrJoin(ctx *plancontext.PlanningContext, lhs, rhs Operator, joinPredic
 		}
 
 		join := NewApplyJoin(ctx, Clone(rhs), Clone(lhs), nil, !inner)
-		newOp := pushJoinPredicates(ctx, joinPredicates, join)
-		return newOp, Rewrote("logical join to applyJoin, switching side because LIMIT")
+		for _, pred := range joinPredicates {
+			join.AddJoinPredicate(ctx, pred)
+		}
+		return join, Rewrote("logical join to applyJoin, switching side because LIMIT")
 	}
 
 	join := NewApplyJoin(ctx, Clone(lhs), Clone(rhs), nil, !inner)
-	newOp := pushJoinPredicates(ctx, joinPredicates, join)
-	return newOp, Rewrote("logical join to applyJoin ")
+	for _, pred := range joinPredicates {
+		join.AddJoinPredicate(ctx, pred)
+	}
+
+	return join, Rewrote("logical join to applyJoin ")
 }
 
 func operatorsToRoutes(a, b Operator) (*Route, *Route) {
@@ -583,15 +588,3 @@ func hexEqual(a, b *sqlparser.Literal) bool {
 	}
 	return false
 }
-
-func pushJoinPredicates(ctx *plancontext.PlanningContext, exprs []sqlparser.Expr, op *ApplyJoin) Operator {
-	if len(exprs) == 0 {
-		return op
-	}
-
-	for _, expr := range exprs {
-		AddPredicate(ctx, op, expr, true, newFilterSinglePredicate)
-	}
-
-	return op
-}

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

@@ -808,6 +808,59 @@
       ]
     }
   },
+  {
+    "comment": "Outer join with join predicates that only depend on the inner side",
+    "query": "select 1 from user left join user_extra on user.foo = 42 and user.bar = user_extra.bar",
+    "plan": {
+      "QueryType": "SELECT",
+      "Original": "select 1 from user left join user_extra on user.foo = 42 and user.bar = user_extra.bar",
+      "Instructions": {
+        "OperatorType": "Projection",
+        "Expressions": [
+          "1 as 1"
+        ],
+        "Inputs": [
+          {
+            "OperatorType": "Join",
+            "Variant": "LeftJoin",
+            "JoinVars": {
+              "user_bar": 1,
+              "user_foo": 0
+            },
+            "TableName": "`user`_user_extra",
+            "Inputs": [
+              {
+                "OperatorType": "Route",
+                "Variant": "Scatter",
+                "Keyspace": {
+                  "Name": "user",
+                  "Sharded": true
+                },
+                "FieldQuery": "select `user`.foo, `user`.bar from `user` where 1 != 1",
+                "Query": "select `user`.foo, `user`.bar from `user`",
+                "Table": "`user`"
+              },
+              {
+                "OperatorType": "Route",
+                "Variant": "Scatter",
+                "Keyspace": {
+                  "Name": "user",
+                  "Sharded": true
+                },
+                "FieldQuery": "select 1 from user_extra where 1 != 1",
+                "Query": "select 1 from user_extra where user_extra.bar = :user_bar and :user_foo = 42",
+                "Table": "user_extra"
+              }
+            ]
+          }
+        ]
+      },
+      "TablesUsed": [
+        "user.user",
+        "user.user_extra"
+      ]
+    }
+  },
   {
     "comment": "Parenthesized, single chunk",
     "query": "select user.col from user join (unsharded as m1 join unsharded as m2)",