types: fix unexpected NOT_NULL flags

cmd/explaintest/r/explain.result

@@ -43,4 +43,4 @@ drop view if exists v;
 create view v as select cast(replace(substring_index(substring_index("",',',1),':',-1),'"','') as CHAR(32)) as event_id;
 desc v;
 Field	Type	Null	Key	Default	Extra
-event_id	varchar(32)	YES		NULL	
+event_id	varchar(32)	NO		NULL	

cmd/explaintest/r/explain_easy.result

@@ -613,20 +613,21 @@ HashJoin_7	8002.00	root		right outer join, equal:[eq(test.t.nb, test.t.nb)]
     └─TableFullScan_12	10000.00	cop[tikv]	table:tb	keep order:false, stats:pseudo
 explain select ifnull(t.a, 1) in (select count(*) from t s , t t1 where s.a = t.a and s.a = t1.a) from t;
 id	estRows	task	access object	operator info
-Projection_12	10000.00	root		Column#14
-└─Apply_14	10000.00	root		CARTESIAN left outer semi join, other cond:eq(ifnull(test.t.a, 1), Column#13)
-  ├─TableReader_16(Build)	10000.00	root		data:TableFullScan_15
-  │ └─TableFullScan_15	10000.00	cop[tikv]	table:t	keep order:false, stats:pseudo
-  └─HashAgg_19(Probe)	1.00	root		funcs:count(Column#15)->Column#13
-    └─HashJoin_20	9.99	root		inner join, equal:[eq(test.t.a, test.t.a)]
-      ├─HashAgg_30(Build)	7.99	root		group by:test.t.a, funcs:count(Column#16)->Column#15, funcs:firstrow(test.t.a)->test.t.a
-      │ └─TableReader_31	7.99	root		data:HashAgg_25
-      │   └─HashAgg_25	7.99	cop[tikv]		group by:test.t.a, funcs:count(1)->Column#16
-      │     └─Selection_29	9.99	cop[tikv]		eq(test.t.a, test.t.a), not(isnull(test.t.a))
-      │       └─TableFullScan_28	10000.00	cop[tikv]	table:t1	keep order:false, stats:pseudo
-      └─TableReader_24(Probe)	9.99	root		data:Selection_23
-        └─Selection_23	9.99	cop[tikv]		eq(test.t.a, test.t.a), not(isnull(test.t.a))
-          └─TableFullScan_22	10000.00	cop[tikv]	table:s	keep order:false, stats:pseudo
+Projection_13	10000.00	root		Column#14
+└─Apply_15	10000.00	root		left outer semi join, equal:[eq(Column#15, Column#13)]
+  ├─Projection_16(Build)	10000.00	root		test.t.a, ifnull(test.t.a, 1)->Column#15
+  │ └─TableReader_18	10000.00	root		data:TableFullScan_17
+  │   └─TableFullScan_17	10000.00	cop[tikv]	table:t	keep order:false, stats:pseudo
+  └─HashAgg_21(Probe)	1.00	root		funcs:count(Column#17)->Column#13
+    └─HashJoin_22	9.99	root		inner join, equal:[eq(test.t.a, test.t.a)]
+      ├─HashAgg_32(Build)	7.99	root		group by:test.t.a, funcs:count(Column#18)->Column#17, funcs:firstrow(test.t.a)->test.t.a
+      │ └─TableReader_33	7.99	root		data:HashAgg_27
+      │   └─HashAgg_27	7.99	cop[tikv]		group by:test.t.a, funcs:count(1)->Column#18
+      │     └─Selection_31	9.99	cop[tikv]		eq(test.t.a, test.t.a), not(isnull(test.t.a))
+      │       └─TableFullScan_30	10000.00	cop[tikv]	table:t1	keep order:false, stats:pseudo
+      └─TableReader_26(Probe)	9.99	root		data:Selection_25
+        └─Selection_25	9.99	cop[tikv]		eq(test.t.a, test.t.a), not(isnull(test.t.a))
+          └─TableFullScan_24	10000.00	cop[tikv]	table:s	keep order:false, stats:pseudo
 drop table if exists t;
 create table t(a int);
 explain select * from t where _tidb_rowid = 0;

expression/builtin_control.go

@@ -193,6 +193,12 @@ func (c *caseWhenFunctionClass) getFunction(ctx sessionctx.Context, args []Expre
 		fieldTp.Flen, fieldTp.Decimal = 0, types.UnspecifiedLength
 		types.SetBinChsClnFlag(fieldTp)
 	}
+	// it's hard to distinguish not null flag, because
+	// 1. the args[0] may be null
+	// 2. no ELSE part
+	// and MySQL 8.0 also does not provide any not null flag in CASE WHEN
+	fieldTp.Flag &^= mysql.NotNullFlag
+
 	argTps := make([]types.EvalType, 0, l)
 	for i := 0; i < l-1; i += 2 {
 		if args[i], err = wrapWithIsTrue(ctx, true, args[i], false); err != nil {

expression/builtin_time.go

@@ -2027,6 +2027,8 @@ func (c *sysDateFunctionClass) getFunction(ctx sessionctx.Context, args []Expres
 		return nil, err
 	}
 	bf.tp.Flen, bf.tp.Decimal = 19, 0
+	// Illegal parameters have been filtered out in the parser, so the result is always not null.
+	bf.tp.Flag |= mysql.NotNullFlag
 
 	var sig builtinFunc
 	if len(args) == 1 {

expression/constant.go

@@ -15,6 +15,7 @@ package expression
 
 import (
 	"fmt"
+	"sync"
 
 	"github.com/pingcap/parser/mysql"
 	"github.com/pingcap/parser/terror"
@@ -56,7 +57,9 @@ func NewNull() *Constant {
 
 // Constant stands for a constant value.
 type Constant struct {
-	Value   types.Datum
+	Value types.Datum
+	// once protects the changes of RetType
+	lock    sync.Mutex
 	RetType *types.FieldType
 	// DeferredExpr holds deferred function in PlanCache cached plan.
 	// it's only used to represent non-deterministic functions(see expression.DeferredFunctions)
@@ -70,6 +73,19 @@ type Constant struct {
 	collationInfo
 }
 
+// Clone implements Expression interface.
+func (c *Constant) Clone() Expression {
+	con := &Constant{
+		Value:         c.Value,
+		RetType:       c.RetType,
+		DeferredExpr:  c.DeferredExpr,
+		ParamMarker:   c.ParamMarker,
+		hashcode:      c.hashcode,
+		collationInfo: c.collationInfo,
+	}
+	return con
+}
+
 // ParamMarker indicates param provided by COM_STMT_EXECUTE.
 type ParamMarker struct {
 	ctx   sessionctx.Context
@@ -98,12 +114,6 @@ func (c *Constant) MarshalJSON() ([]byte, error) {
 	return []byte(fmt.Sprintf("%q", c)), nil
 }
 
-// Clone implements Expression interface.
-func (c *Constant) Clone() Expression {
-	con := *c
-	return &con
-}
-
 // GetType implements Expression interface.
 func (c *Constant) GetType() *types.FieldType {
 	if c.ParamMarker != nil {
@@ -114,6 +124,23 @@ func (c *Constant) GetType() *types.FieldType {
 		types.DefaultParamTypeForValue(dt.GetValue(), tp)
 		return tp
 	}
+	if !c.Value.IsNull() {
+		// c.once.Do(func() {
+		// 	c.RetType = c.RetType.Clone()
+		// 	c.RetType.Flag |= mysql.NotNullFlag
+		// })
+		// tp := c.RetType.Clone()
+		// tp.Flag |= mysql.NotNullFlag
+		// return tp
+
+		c.lock.Lock()
+		c.RetType.Flag |= mysql.NotNullFlag
+		c.lock.Unlock()
+	} else {
+		c.lock.Lock()
+		c.RetType.Flag &^= mysql.NotNullFlag
+		c.lock.Unlock()
+	}
 	return c.RetType
 }
 

expression/integration_test.go

@@ -2875,6 +2875,19 @@ func (s *testIntegrationSuite2) TestBuiltin(c *C) {
 	result.Check(testkit.Rows("<nil> 4"))
 	result = tk.MustQuery("select * from t where b = case when a is null then 4 when  a = 'str5' then 7 else 9 end")
 	result.Check(testkit.Rows("<nil> 4"))
+	result = tk.MustQuery(`SELECT -Max(+23) * -+Cast(--10 AS SIGNED) * -CASE
+                                               WHEN 0 > 85 THEN NULL
+                                               WHEN NOT
+              CASE +55
+                WHEN +( +82 ) + -89 * -69 THEN +Count(-88)
+                WHEN +CASE 57
+                        WHEN +89 THEN -89 * Count(*)
+                        WHEN 17 THEN NULL
+                      END THEN ( -10 )
+              END IS NULL THEN NULL
+                                               ELSE 83 + 48
+                                             END AS col0; `)
+	result.Check(testkit.Rows("-30130"))
 	// test warnings
 	tk.MustQuery("select case when b=0 then 1 else 1/b end from t")
 	tk.MustQuery("show warnings").Check(testkit.Rows())

expression/simple_rewriter.go

@@ -57,7 +57,7 @@ func ParseSimpleExprCastWithTableInfo(ctx sessionctx.Context, exprStr string, ta
 	if err != nil {
 		return nil, err
 	}
-	e = BuildCastFunction(ctx, e, targetFt)
+	e = BuildCastFunction(ctx, e, targetFt.Clone())
 	return e, nil
 }