plan: push down constant filters over join properly (pingcap#9848)

cmd/explaintest/r/explain_easy.result

@@ -307,6 +307,50 @@ Projection_11	10000.00	root	9_aux_0
       │ └─TableScan_27	10000.00	cop	table:t, keep order:false, stats:pseudo
       └─TableReader_32	1.00	root	data:TableScan_31
         └─TableScan_31	1.00	cop	table:t1, range: decided by [s.c], keep order:false, stats:pseudo
+insert into t values(1, 1, 1), (2, 2 ,2), (3, 3, 3), (4, 3, 4),(5,3,5);
+analyze table t;
+explain select t.c in (select count(*) from t s, t t1 where s.b = t.a and s.b = 3 and s.a = t1.a) from t;
+id	count	task	operator info
+Projection_11	5.00	root	9_aux_0
+└─Apply_13	5.00	root	left outer semi join, inner:StreamAgg_20, other cond:eq(test.t.c, 7_col_0)
+  ├─TableReader_15	5.00	root	data:TableScan_14
+  │ └─TableScan_14	5.00	cop	table:t, range:[-inf,+inf], keep order:false
+  └─StreamAgg_20	1.00	root	funcs:count(1)
+    └─IndexJoin_49	2.40	root	inner join, inner:TableReader_48, outer key:s.a, inner key:t1.a
+      ├─IndexReader_41	2.40	root	index:Selection_40
+      │ └─Selection_40	2.40	cop	eq(3, test.t.a)
+      │   └─IndexScan_39	3.00	cop	table:s, index:b, range:[3,3], keep order:false
+      └─TableReader_48	0.80	root	data:Selection_47
+        └─Selection_47	0.80	cop	eq(3, test.t.a)
+          └─TableScan_46	1.00	cop	table:t1, range: decided by [s.a], keep order:false
+explain select t.c in (select count(*) from t s left join t t1 on s.a = t1.a where 3 = t.a and s.b = 3) from t;
+id	count	task	operator info
+Projection_10	5.00	root	9_aux_0
+└─Apply_12	5.00	root	left outer semi join, inner:StreamAgg_19, other cond:eq(test.t.c, 7_col_0)
+  ├─TableReader_14	5.00	root	data:TableScan_13
+  │ └─TableScan_13	5.00	cop	table:t, range:[-inf,+inf], keep order:false
+  └─StreamAgg_19	1.00	root	funcs:count(1)
+    └─IndexJoin_43	2.40	root	left outer join, inner:TableReader_42, outer key:s.a, inner key:t1.a
+      ├─IndexReader_35	2.40	root	index:Selection_34
+      │ └─Selection_34	2.40	cop	eq(3, test.t.a)
+      │   └─IndexScan_33	3.00	cop	table:s, index:b, range:[3,3], keep order:false
+      └─TableReader_42	0.80	root	data:Selection_41
+        └─Selection_41	0.80	cop	eq(3, test.t.a)
+          └─TableScan_40	1.00	cop	table:t1, range: decided by [s.a], keep order:false
+explain select t.c in (select count(*) from t s right join t t1 on s.a = t1.a where 3 = t.a and t1.b = 3) from t;
+id	count	task	operator info
+Projection_10	5.00	root	9_aux_0
+└─Apply_12	5.00	root	left outer semi join, inner:StreamAgg_19, other cond:eq(test.t.c, 7_col_0)
+  ├─TableReader_14	5.00	root	data:TableScan_13
+  │ └─TableScan_13	5.00	cop	table:t, range:[-inf,+inf], keep order:false
+  └─StreamAgg_19	1.00	root	funcs:count(1)
+    └─IndexJoin_43	2.40	root	right outer join, inner:TableReader_42, outer key:t1.a, inner key:s.a
+      ├─TableReader_42	0.80	root	data:Selection_41
+      │ └─Selection_41	0.80	cop	eq(3, test.t.a)
+      │   └─TableScan_40	1.00	cop	table:s, range: decided by [t1.a], keep order:false
+      └─IndexReader_35	2.40	root	index:Selection_34
+        └─Selection_34	2.40	cop	eq(3, test.t.a)
+          └─IndexScan_33	3.00	cop	table:t1, index:b, range:[3,3], keep order:false
 drop table if exists t;
 create table t(a int unsigned);
 explain select t.a = '123455' from t;

cmd/explaintest/t/explain_easy.test

@@ -52,6 +52,12 @@ explain select t.c in (select count(*) from t s ignore index(idx), t t1 where s.
 explain select t.c in (select count(*) from t s use index(idx), t t1 where s.b = t.a and s.a = t1.a) from t;
 explain select t.c in (select count(*) from t s use index(idx), t t1 where s.b = t.a and s.c = t1.a) from t;
 
+insert into t values(1, 1, 1), (2, 2 ,2), (3, 3, 3), (4, 3, 4),(5,3,5);
+analyze table t;
+explain select t.c in (select count(*) from t s, t t1 where s.b = t.a and s.b = 3 and s.a = t1.a) from t;
+explain select t.c in (select count(*) from t s left join t t1 on s.a = t1.a where 3 = t.a and s.b = 3) from t;
+explain select t.c in (select count(*) from t s right join t t1 on s.a = t1.a where 3 = t.a and t1.b = 3) from t;
+
 drop table if exists t;
 create table t(a int unsigned);
 explain select t.a = '123455' from t;

planner/core/logical_plan_builder.go

@@ -176,6 +176,35 @@ func (b *planBuilder) buildResultSetNode(node ast.ResultSetNode) (p LogicalPlan,
 	}
 }
 
+// pushDownConstExpr checks if the condition is from filter condition, if true, push it down to both
+// children of join, whatever the join type is; if false, push it down to inner child of outer join,
+// and both children of non-outer-join.
+func (p *LogicalJoin) pushDownConstExpr(expr expression.Expression, leftCond []expression.Expression,
+	rightCond []expression.Expression, filterCond bool) ([]expression.Expression, []expression.Expression) {
+	switch p.JoinType {
+	case LeftOuterJoin, LeftOuterSemiJoin, AntiLeftOuterSemiJoin:
+		if filterCond {
+			leftCond = append(leftCond, expr)
+			// Append the expr to right join condition instead of `rightCond`, to make it able to be
+			// pushed down to children of join.
+			p.RightConditions = append(p.RightConditions, expr)
+		} else {
+			rightCond = append(rightCond, expr)
+		}
+	case RightOuterJoin:
+		if filterCond {
+			rightCond = append(rightCond, expr)
+			p.LeftConditions = append(p.LeftConditions, expr)
+		} else {
+			leftCond = append(leftCond, expr)
+		}
+	case SemiJoin, AntiSemiJoin, InnerJoin:
+		leftCond = append(leftCond, expr)
+		rightCond = append(rightCond, expr)
+	}
+	return leftCond, rightCond
+}
+
 // extractOnCondition divide conditions in CNF of join node into 4 groups.
 // These conditions can be where conditions, join conditions, or collection of both.
 // If deriveLeft/deriveRight is set, we would try to derive more conditions for left/right plan.
@@ -205,6 +234,12 @@ func extractOnCondition(conditions []expression.Expression, left LogicalPlan, ri
 			}
 		}
 		columns := expression.ExtractColumns(expr)
+		// `columns` may be empty, if the condition is like `correlated_column op constant`, or `constant`,
+		// push this kind of constant condition down according to join type.
+		if len(columns) == 0 {
+			leftCond, rightCond = p.pushDownConstExpr(expr, leftCond, rightCond, deriveLeft || deriveRight)
+			continue
+		}
 		allFromLeft, allFromRight := true, true
 		for _, col := range columns {
 			if !left.Schema().Contains(col) {

planner/core/logical_plan_test.go

@@ -994,7 +994,7 @@ func (s *testPlanSuite) TestJoinReOrder(c *C) {
 		},
 		{
 			sql:  "select * from t o where o.b in (select t3.c from t t1, t t2, t t3 where t1.a = t3.a and t2.a = t3.a and t2.a = o.a and t1.a = 1)",
-			best: "Apply{DataScan(o)->Join{Join{DataScan(t1)->DataScan(t3)}->DataScan(t2)}->Projection}->Projection",
+			best: "Apply{DataScan(o)->Join{Join{DataScan(t1)->DataScan(t2)}->DataScan(t3)}->Projection}->Projection",
 		},
 	}
 	for _, tt := range tests {