cherry pick pingcap#37117 to release-6.2

Signed-off-by: ti-srebot <ti-srebot@pingcap.com>

cmd/explaintest/r/subquery.result

@@ -46,3 +46,31 @@ create table t1(a int(11));
 create table t2(a decimal(40,20) unsigned, b decimal(40,20));
 select count(*) as x from t1 group by a having x not in (select a from t2 where x = t2.b);
 x
+drop table if exists stu;
+drop table if exists exam;
+create table stu(id int, name varchar(100));
+insert into stu values(1, null);
+create table exam(stu_id int, course varchar(100), grade int);
+insert into exam values(1, 'math', 100);
+set names utf8 collate utf8_general_ci;
+explain format = 'brief' select * from stu where stu.name not in (select 'guo' from exam where exam.stu_id = stu.id);
+id	estRows	task	access object	operator info
+Apply	10000.00	root		CARTESIAN anti semi join, other cond:eq(test.stu.name, Column#8)
+├─TableReader(Build)	10000.00	root		data:TableFullScan
+│ └─TableFullScan	10000.00	cop[tikv]	table:stu	keep order:false, stats:pseudo
+└─Projection(Probe)	10.00	root		guo->Column#8
+  └─TableReader	10.00	root		data:Selection
+    └─Selection	10.00	cop[tikv]		eq(test.exam.stu_id, test.stu.id)
+      └─TableFullScan	10000.00	cop[tikv]	table:exam	keep order:false, stats:pseudo
+select * from stu where stu.name not in (select 'guo' from exam where exam.stu_id = stu.id);
+id	name
+set names utf8mb4;
+explain format = 'brief' select * from stu where stu.name not in (select 'guo' from exam where exam.stu_id = stu.id);
+id	estRows	task	access object	operator info
+HashJoin	8000.00	root		anti semi join, equal:[eq(test.stu.id, test.exam.stu_id)], other cond:eq(test.stu.name, "guo")
+├─TableReader(Build)	10000.00	root		data:TableFullScan
+│ └─TableFullScan	10000.00	cop[tikv]	table:exam	keep order:false, stats:pseudo
+└─TableReader(Probe)	10000.00	root		data:TableFullScan
+  └─TableFullScan	10000.00	cop[tikv]	table:stu	keep order:false, stats:pseudo
+select * from stu where stu.name not in (select 'guo' from exam where exam.stu_id = stu.id);
+id	name

cmd/explaintest/t/subquery.test

@@ -20,3 +20,16 @@ drop table if exists t1, t2;
 create table t1(a int(11));
 create table t2(a decimal(40,20) unsigned, b decimal(40,20));
 select count(*) as x from t1 group by a having x not in (select a from t2 where x = t2.b);
+
+drop table if exists stu;
+drop table if exists exam;
+create table stu(id int, name varchar(100));
+insert into stu values(1, null);
+create table exam(stu_id int, course varchar(100), grade int);
+insert into exam values(1, 'math', 100);
+set names utf8 collate utf8_general_ci;
+explain format = 'brief' select * from stu where stu.name not in (select 'guo' from exam where exam.stu_id = stu.id);
+select * from stu where stu.name not in (select 'guo' from exam where exam.stu_id = stu.id);
+set names utf8mb4;
+explain format = 'brief' select * from stu where stu.name not in (select 'guo' from exam where exam.stu_id = stu.id);
+select * from stu where stu.name not in (select 'guo' from exam where exam.stu_id = stu.id);

expression/util.go

@@ -365,7 +365,8 @@ func extractColumnSet(expr Expression, set *intsets.Sparse) {
 	}
 }
 
-func setExprColumnInOperand(expr Expression) Expression {
+// SetExprColumnInOperand is used to set columns in expr as InOperand.
+func SetExprColumnInOperand(expr Expression) Expression {
 	switch v := expr.(type) {
 	case *Column:
 		col := v.Clone().(*Column)
@@ -374,7 +375,7 @@ func setExprColumnInOperand(expr Expression) Expression {
 	case *ScalarFunction:
 		args := v.GetArgs()
 		for i, arg := range args {
-			args[i] = setExprColumnInOperand(arg)
+			args[i] = SetExprColumnInOperand(arg)
 		}
 	}
 	return expr
@@ -383,44 +384,65 @@ func setExprColumnInOperand(expr Expression) Expression {
 // ColumnSubstitute substitutes the columns in filter to expressions in select fields.
 // e.g. select * from (select b as a from t) k where a < 10 => select * from (select b as a from t where b < 10) k.
 func ColumnSubstitute(expr Expression, schema *Schema, newExprs []Expression) Expression {
-	_, resExpr := ColumnSubstituteImpl(expr, schema, newExprs)
+	_, _, resExpr := ColumnSubstituteImpl(expr, schema, newExprs, false)
 	return resExpr
 }
 
+// ColumnSubstituteAll substitutes the columns just like ColumnSubstitute, but we don't accept partial substitution.
+// Only accept:
+//
+//	1: substitute them all once find col in schema.
+//	2: nothing in expr can be substituted.
+func ColumnSubstituteAll(expr Expression, schema *Schema, newExprs []Expression) (bool, Expression) {
+	_, hasFail, resExpr := ColumnSubstituteImpl(expr, schema, newExprs, true)
+	return hasFail, resExpr
+}
+
 // ColumnSubstituteImpl tries to substitute column expr using newExprs,
 // the newFunctionInternal is only called if its child is substituted
-func ColumnSubstituteImpl(expr Expression, schema *Schema, newExprs []Expression) (bool, Expression) {
+// @return bool means whether the expr has changed.
+// @return bool means whether the expr should change (has the dependency in schema, while the corresponding expr has some compatibility), but finally fallback.
+// @return Expression, the original expr or the changed expr, it depends on the first @return bool.
+func ColumnSubstituteImpl(expr Expression, schema *Schema, newExprs []Expression, fail1Return bool) (bool, bool, Expression) {
 	switch v := expr.(type) {
 	case *Column:
 		id := schema.ColumnIndex(v)
 		if id == -1 {
-			return false, v
+			return false, false, v
 		}
 		newExpr := newExprs[id]
 		if v.InOperand {
-			newExpr = setExprColumnInOperand(newExpr)
+			newExpr = SetExprColumnInOperand(newExpr)
 		}
 		newExpr.SetCoercibility(v.Coercibility())
-		return true, newExpr
+		return true, false, newExpr
 	case *ScalarFunction:
 		substituted := false
+		hasFail := false
 		if v.FuncName.L == ast.Cast {
 			newFunc := v.Clone().(*ScalarFunction)
-			substituted, newFunc.GetArgs()[0] = ColumnSubstituteImpl(newFunc.GetArgs()[0], schema, newExprs)
+			substituted, hasFail, newFunc.GetArgs()[0] = ColumnSubstituteImpl(newFunc.GetArgs()[0], schema, newExprs, fail1Return)
+			if fail1Return && hasFail {
+				return substituted, hasFail, newFunc
+			}
 			if substituted {
 				// Workaround for issue https://github.com/pingcap/tidb/issues/28804
 				e := NewFunctionInternal(v.GetCtx(), v.FuncName.L, v.RetType, newFunc.GetArgs()...)
 				e.SetCoercibility(v.Coercibility())
-				return true, e
+				return true, false, e
 			}
-			return false, newFunc
+			return false, false, newFunc
 		}
 		// cowExprRef is a copy-on-write util, args array allocation happens only
 		// when expr in args is changed
 		refExprArr := cowExprRef{v.GetArgs(), nil}
 		_, coll := DeriveCollationFromExprs(v.GetCtx(), v.GetArgs()...)
 		for idx, arg := range v.GetArgs() {
-			changed, newFuncExpr := ColumnSubstituteImpl(arg, schema, newExprs)
+			changed, hasFail, newFuncExpr := ColumnSubstituteImpl(arg, schema, newExprs, fail1Return)
+			if fail1Return && hasFail {
+				return changed, hasFail, v
+			}
+			oldChanged := changed
 			if collate.NewCollationEnabled() {
 				// Make sure the collation used by the ScalarFunction isn't changed and its result collation is not weaker than the collation used by the ScalarFunction.
 				if changed {
@@ -433,16 +455,24 @@ func ColumnSubstituteImpl(expr Expression, schema *Schema, newExprs []Expression
 					}
 				}
 			}
+			if fail1Return && oldChanged != changed {
+				// Only when the oldChanged is true and changed is false, we will get here.
+				// And this means there some dependency in this arg can be substituted with
+				// given expressions, while it has some collation compatibility, finally we
+				// fall back to use the origin args. (commonly used in projection elimination
+				// in which fallback usage is unacceptable)
+				return changed, true, v
+			}
 			refExprArr.Set(idx, changed, newFuncExpr)
 			if changed {
 				substituted = true
 			}
 		}
 		if substituted {
-			return true, NewFunctionInternal(v.GetCtx(), v.FuncName.L, v.RetType, refExprArr.Result()...)
+			return true, false, NewFunctionInternal(v.GetCtx(), v.FuncName.L, v.RetType, refExprArr.Result()...)
 		}
 	}
-	return false, expr
+	return false, false, expr
 }
 
 // checkCollationStrictness check collation strictness-ship between `coll` and `newFuncColl`

expression/util_test.go

@@ -193,12 +193,12 @@ func TestGetUint64FromConstant(t *testing.T) {
 
 func TestSetExprColumnInOperand(t *testing.T) {
 	col := &Column{RetType: newIntFieldType()}
-	require.True(t, setExprColumnInOperand(col).(*Column).InOperand)
+	require.True(t, SetExprColumnInOperand(col).(*Column).InOperand)
 
 	f, err := funcs[ast.Abs].getFunction(mock.NewContext(), []Expression{col})
 	require.NoError(t, err)
 	fun := &ScalarFunction{Function: f}
-	setExprColumnInOperand(fun)
+	SetExprColumnInOperand(fun)
 	require.True(t, f.getArgs()[0].(*Column).InOperand)
 }
 

planner/core/expression_rewriter.go

@@ -479,6 +479,7 @@ func (er *expressionRewriter) buildSemiApplyFromEqualSubq(np LogicalPlan, l, r e
 				rColCopy := *rCol
 				rColCopy.InOperand = true
 				r = &rColCopy
+				l = expression.SetExprColumnInOperand(l)
 			}
 		} else {
 			rowFunc := r.(*expression.ScalarFunction)
@@ -501,6 +502,7 @@ func (er *expressionRewriter) buildSemiApplyFromEqualSubq(np LogicalPlan, l, r e
 				if er.err != nil {
 					return
 				}
+				l = expression.SetExprColumnInOperand(l)
 			}
 		}
 	}
@@ -912,22 +914,31 @@ func (er *expressionRewriter) handleInSubquery(ctx context.Context, v *ast.Patte
 		// normal column equal condition, so we specially mark the inner operand here.
 		if v.Not || asScalar {
 			// If both input columns of `in` expression are not null, we can treat the expression
-			// as normal column equal condition instead.
+			// as normal column equal condition instead. Otherwise, mark the left and right side.
+			// eg: for some optimization, the column substitute in right side in projection elimination
+			// will cause case  like <lcol EQ rcol(inOperand)> as <lcol EQ constant> which is not
+			// a valid null-aware EQ. (null in lcol still need to be null-aware)
 			if !expression.ExprNotNull(lexpr) || !expression.ExprNotNull(rCol) {
 				rColCopy := *rCol
 				rColCopy.InOperand = true
 				rexpr = &rColCopy
+				lexpr = expression.SetExprColumnInOperand(lexpr)
 			}
 		}
 	} else {
 		args := make([]expression.Expression, 0, np.Schema().Len())
 		for i, col := range np.Schema().Columns {
 			if v.Not || asScalar {
 				larg := expression.GetFuncArg(lexpr, i)
+				// If both input columns of `in` expression are not null, we can treat the expression
+				// as normal column equal condition instead. Otherwise, mark the left and right side.
 				if !expression.ExprNotNull(larg) || !expression.ExprNotNull(col) {
 					rarg := *col
 					rarg.InOperand = true
 					col = &rarg
+					if larg != nil {
+						lexpr.(*expression.ScalarFunction).GetArgs()[i] = expression.SetExprColumnInOperand(larg)
+					}
 				}
 			}
 			args = append(args, col)

planner/core/logical_plans.go

@@ -375,21 +375,70 @@ func (p *LogicalJoin) GetPotentialPartitionKeys() (leftKeys, rightKeys []*proper
 	return
 }
 
-func (p *LogicalJoin) columnSubstitute(schema *expression.Schema, exprs []expression.Expression) {
+// decorrelate eliminate the correlated column with if the col is in schema.
+func (p *LogicalJoin) decorrelate(schema *expression.Schema) {
 	for i, cond := range p.LeftConditions {
-		p.LeftConditions[i] = expression.ColumnSubstitute(cond, schema, exprs)
+		p.LeftConditions[i] = cond.Decorrelate(schema)
 	}
-
 	for i, cond := range p.RightConditions {
-		p.RightConditions[i] = expression.ColumnSubstitute(cond, schema, exprs)
+		p.RightConditions[i] = cond.Decorrelate(schema)
 	}
-
 	for i, cond := range p.OtherConditions {
-		p.OtherConditions[i] = expression.ColumnSubstitute(cond, schema, exprs)
+		p.OtherConditions[i] = cond.Decorrelate(schema)
+	}
+	for i, cond := range p.EqualConditions {
+		p.EqualConditions[i] = cond.Decorrelate(schema).(*expression.ScalarFunction)
+	}
+}
+
+// columnSubstituteAll is used in projection elimination in apply de-correlation.
+// Substitutions for all conditions should be successful, otherwise, we should keep all conditions unchanged.
+func (p *LogicalJoin) columnSubstituteAll(schema *expression.Schema, exprs []expression.Expression) (hasFail bool) {
+	// make a copy of exprs for convenience of substitution (may change/partially change the expr tree)
+	cpLeftConditions := make(expression.CNFExprs, len(p.LeftConditions))
+	cpRightConditions := make(expression.CNFExprs, len(p.RightConditions))
+	cpOtherConditions := make(expression.CNFExprs, len(p.OtherConditions))
+	cpEqualConditions := make([]*expression.ScalarFunction, len(p.EqualConditions))
+	copy(cpLeftConditions, p.LeftConditions)
+	copy(cpRightConditions, p.RightConditions)
+	copy(cpOtherConditions, p.OtherConditions)
+	copy(cpEqualConditions, p.EqualConditions)
+
+	// try to substitute columns in these condition.
+	for i, cond := range cpLeftConditions {
+		if hasFail, cpLeftConditions[i] = expression.ColumnSubstituteAll(cond, schema, exprs); hasFail {
+			return
+		}
+	}
+
+	for i, cond := range cpRightConditions {
+		if hasFail, cpRightConditions[i] = expression.ColumnSubstituteAll(cond, schema, exprs); hasFail {
+			return
+		}
+	}
+
+	for i, cond := range cpOtherConditions {
+		if hasFail, cpOtherConditions[i] = expression.ColumnSubstituteAll(cond, schema, exprs); hasFail {
+			return
+		}
 	}
 
+	for i, cond := range cpEqualConditions {
+		var tmp expression.Expression
+		if hasFail, tmp = expression.ColumnSubstituteAll(cond, schema, exprs); hasFail {
+			return
+		}
+		cpEqualConditions[i] = tmp.(*expression.ScalarFunction)
+	}
+
+	// if all substituted, change them atomically here.
+	p.LeftConditions = cpLeftConditions
+	p.RightConditions = cpRightConditions
+	p.OtherConditions = cpOtherConditions
+	p.EqualConditions = cpEqualConditions
+
 	for i := len(p.EqualConditions) - 1; i >= 0; i-- {
-		newCond := expression.ColumnSubstitute(p.EqualConditions[i], schema, exprs).(*expression.ScalarFunction)
+		newCond := p.EqualConditions[i]
 
 		// If the columns used in the new filter all come from the left child,
 		// we can push this filter to it.
@@ -420,6 +469,7 @@ func (p *LogicalJoin) columnSubstitute(schema *expression.Schema, exprs []expres
 
 		p.EqualConditions[i] = newCond
 	}
+	return false
 }
 
 // AttachOnConds extracts on conditions for join and set the `EqualConditions`, `LeftConditions`, `RightConditions` and

planner/core/rule_decorrelate.go

@@ -171,10 +171,28 @@ func (s *decorrelateSolver) optimize(ctx context.Context, p LogicalPlan, opt *lo
 				// TODO: Actually, it can be optimized. We need to first push the projection down to the selection. And then the APPLY can be decorrelated.
 				goto NoOptimize
 			}
+
+			// step1: substitute the all the schema with new expressions (including correlated column maybe, but it doesn't affect the collation infer inside)
+			// eg: projection: constant("guo") --> column8, once upper layer substitution failed here, the lower layer behind
+			// projection can't supply column8 anymore.
+			//
+			//	upper OP (depend on column8)   --> projection(constant "guo" --> column8)  --> lower layer OP
+			//	          |                                                       ^
+			//	          +-------------------------------------------------------+
+			//
+			//	upper OP (depend on column8)   --> lower layer OP
+			//	          |                             ^
+			//	          +-----------------------------+      // Fail: lower layer can't supply column8 anymore.
+			hasFail := apply.columnSubstituteAll(proj.Schema(), proj.Exprs)
+			if hasFail {
+				goto NoOptimize
+			}
+			// step2: when it can be substituted all, we then just do the de-correlation (apply conditions included).
 			for i, expr := range proj.Exprs {
 				proj.Exprs[i] = expr.Decorrelate(outerPlan.Schema())
 			}
-			apply.columnSubstitute(proj.Schema(), proj.Exprs)
+			apply.decorrelate(outerPlan.Schema())
+
 			innerPlan = proj.children[0]
 			apply.SetChildren(outerPlan, innerPlan)
 			if apply.JoinType != SemiJoin && apply.JoinType != LeftOuterSemiJoin && apply.JoinType != AntiSemiJoin && apply.JoinType != AntiLeftOuterSemiJoin {