planner: fix wrong behavior for = all() (#52801)

cmd/explaintest/r/select.result

@@ -413,7 +413,7 @@ explain format = 'brief' select a = all (select a from t t2) from t t1;
 id	estRows	task	access object	operator info
 Projection	10000.00	root		or(and(and(le(Column#11, 1), eq(test.t.a, Column#10)), if(ne(Column#12, 0), <nil>, 1)), or(eq(Column#13, 0), if(isnull(test.t.a), <nil>, 0)))->Column#14
 └─HashJoin	10000.00	root		CARTESIAN inner join
-  ├─StreamAgg(Build)	1.00	root		funcs:firstrow(Column#16)->Column#10, funcs:count(distinct Column#17)->Column#11, funcs:sum(Column#18)->Column#12, funcs:count(1)->Column#13
+  ├─StreamAgg(Build)	1.00	root		funcs:max(Column#16)->Column#10, funcs:count(distinct Column#17)->Column#11, funcs:sum(Column#18)->Column#12, funcs:count(1)->Column#13
   │ └─Projection	10000.00	root		test.t.a, test.t.a, cast(isnull(test.t.a), decimal(20,0) BINARY)->Column#18
   │   └─TableReader	10000.00	root		data:TableFullScan
   │     └─TableFullScan	10000.00	cop[tikv]	table:t2	keep order:false, stats:pseudo

planner/core/casetest/plan_test.go

@@ -270,3 +270,25 @@ func TestJSONPlanInExplain(t *testing.T) {
 		}
 	}
 }
+
+func TestHandleEQAll(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec("CREATE TABLE t1 (c1 int, c2 int, UNIQUE i1 (c1, c2));")
+	tk.MustExec("INSERT INTO t1 VALUES (7, null),(5,1);")
+	tk.MustQuery("SELECT c1 FROM t1 WHERE ('m' = ALL (SELECT /*+ IGNORE_INDEX(t1, i1) */ c2 FROM t1)) IS NOT UNKNOWN; ").Check(testkit.Rows("5", "7"))
+	tk.MustQuery("SELECT c1 FROM t1 WHERE ('m' = ALL (SELECT /*+ use_INDEX(t1, i1) */ c2 FROM t1)) IS NOT UNKNOWN; ").Check(testkit.Rows("5", "7"))
+	tk.MustQuery("select (null = ALL (SELECT /*+ NO_INDEX() */ c2 FROM t1)) IS NOT UNKNOWN").Check(testkit.Rows("0"))
+	tk.MustExec("CREATE TABLE t2 (c1 int, c2 int, UNIQUE i1 (c1, c2));")
+	tk.MustExec("INSERT INTO t2 VALUES (7, null),(5,null);")
+	tk.MustQuery("select (null = ALL (SELECT /*+ NO_INDEX() */ c2 FROM t2)) IS NOT UNKNOWN").Check(testkit.Rows("0"))
+	tk.MustQuery("SELECT c1 FROM t2 WHERE ('m' = ALL (SELECT /*+ IGNORE_INDEX(t2, i1) */ c2 FROM t2)) IS NOT UNKNOWN; ").Check(testkit.Rows())
+	tk.MustQuery("SELECT c1 FROM t2 WHERE ('m' = ALL (SELECT /*+ use_INDEX(t2, i1) */ c2 FROM t2)) IS NOT UNKNOWN; ").Check(testkit.Rows())
+	tk.MustExec("truncate table t2")
+	tk.MustExec("INSERT INTO t2 VALUES (7, null),(7,null);")
+	tk.MustQuery("select c1 from t2 where (c1 = all (select /*+ IGNORE_INDEX(t2, i1) */ c1 from t2))").Check(testkit.Rows("7", "7"))
+	tk.MustQuery("select c1 from t2 where (c1 = all (select /*+ use_INDEX(t2, i1) */ c1 from t2))").Check(testkit.Rows("7", "7"))
+	tk.MustQuery("select c2 from t2 where (c2 = all (select /*+ IGNORE_INDEX(t2, i1) */ c2 from t2))").Check(testkit.Rows())
+	tk.MustQuery("select c2 from t2 where (c2 = all (select /*+ use_INDEX(t2, i1) */ c2 from t2))").Check(testkit.Rows())
+}

planner/core/expression_rewriter.go

@@ -778,7 +778,9 @@ func (er *expressionRewriter) handleNEAny(lexpr, rexpr expression.Expression, np
 // handleEQAll handles the case of = all. For example, if the query is t.id = all (select s.id from s), it will be rewrote to
 // t.id = (select s.id from s having count(distinct s.id) <= 1 and [all checker]).
 func (er *expressionRewriter) handleEQAll(lexpr, rexpr expression.Expression, np LogicalPlan, markNoDecorrelate bool) {
-	firstRowFunc, err := aggregation.NewAggFuncDesc(er.sctx, ast.AggFuncFirstRow, []expression.Expression{rexpr}, false)
+	// If there is NULL in s.id column, s.id should be the value that isn't null in condition t.id == s.id.
+	// So use function max to filter NULL.
+	maxFunc, err := aggregation.NewAggFuncDesc(er.sctx, ast.AggFuncMax, []expression.Expression{rexpr}, false)
 	if err != nil {
 		er.err = err
 		return
@@ -789,37 +791,27 @@ func (er *expressionRewriter) handleEQAll(lexpr, rexpr expression.Expression, np
 		return
 	}
 	plan4Agg := LogicalAggregation{
-		AggFuncs: []*aggregation.AggFuncDesc{firstRowFunc, countFunc},
+		AggFuncs: []*aggregation.AggFuncDesc{maxFunc, countFunc},
 	}.Init(er.sctx, er.b.getSelectOffset())
 	if hint := er.b.TableHints(); hint != nil {
 		plan4Agg.aggHints = hint.aggHints
 	}
 	plan4Agg.SetChildren(np)
 	plan4Agg.names = append(plan4Agg.names, types.EmptyName)
 
-	// Currently, firstrow agg function is treated like the exact representation of aggregate group key,
-	// so the data type is the same with group key, even if the group key is not null.
-	// However, the return type of firstrow should be nullable, we clear the null flag here instead of
-	// during invoking NewAggFuncDesc, in order to keep compatibility with the existing presumption
-	// that the return type firstrow does not change nullability, whatsoever.
-	// Cloning it because the return type is the same object with argument's data type.
-	newRetTp := firstRowFunc.RetTp.Clone()
-	newRetTp.DelFlag(mysql.NotNullFlag)
-	firstRowFunc.RetTp = newRetTp
-
-	firstRowResultCol := &expression.Column{
+	maxResultCol := &expression.Column{
 		UniqueID: er.sctx.GetSessionVars().AllocPlanColumnID(),
-		RetType:  firstRowFunc.RetTp,
+		RetType:  maxFunc.RetTp,
 	}
-	firstRowResultCol.SetCoercibility(rexpr.Coercibility())
+	maxResultCol.SetCoercibility(rexpr.Coercibility())
 	plan4Agg.names = append(plan4Agg.names, types.EmptyName)
 	count := &expression.Column{
 		UniqueID: er.sctx.GetSessionVars().AllocPlanColumnID(),
 		RetType:  countFunc.RetTp,
 	}
-	plan4Agg.SetSchema(expression.NewSchema(firstRowResultCol, count))
+	plan4Agg.SetSchema(expression.NewSchema(maxResultCol, count))
 	leFunc := expression.NewFunctionInternal(er.sctx, ast.LE, types.NewFieldType(mysql.TypeTiny), count, expression.NewOne())
-	eqCond := expression.NewFunctionInternal(er.sctx, ast.EQ, types.NewFieldType(mysql.TypeTiny), lexpr, firstRowResultCol)
+	eqCond := expression.NewFunctionInternal(er.sctx, ast.EQ, types.NewFieldType(mysql.TypeTiny), lexpr, maxResultCol)
 	cond := expression.ComposeCNFCondition(er.sctx, leFunc, eqCond)
 	er.buildQuantifierPlan(plan4Agg, cond, lexpr, rexpr, true, markNoDecorrelate)
 }