Merge branch 'release-4.0' into release-4.0-f3c64ceecefd

pingcap · Mar 16, 2021 · f7f00ed · f7f00ed
2 parents ead41d9 + a6d8bcb
commit f7f00ed
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Showing 3 changed files with 17 additions and 3 deletions.
diff --git a/expression/builtin_control.go b/expression/builtin_control.go
@@ -176,6 +176,9 @@ func (c *caseWhenFunctionClass) getFunction(ctx sessionctx.Context, args []Expre
 	}
 
 	fieldTp := types.AggFieldType(fieldTps)
+	// Here we turn off NotNullFlag. Because if all when-clauses are false,
+	// the result of case-when expr is NULL.
+	types.SetTypeFlag(&fieldTp.Flag, mysql.NotNullFlag, false)
 	tp := fieldTp.EvalType()
 
 	if tp == types.ETInt {

diff --git a/expression/integration_test.go b/expression/integration_test.go
@@ -2920,6 +2920,16 @@ 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"))
+
+	// return type of case when expr should not include NotNullFlag. issue-23036
+	tk.MustExec("drop table if exists t1")
+	tk.MustExec("create table t1(c1 int not null)")
+	tk.MustExec("insert into t1 values(1)")
+	result = tk.MustQuery("select (case when null then c1 end) is null from t1")
+	result.Check(testkit.Rows("1"))
+	result = tk.MustQuery("select (case when null then c1 end) is not null from t1")
+	result.Check(testkit.Rows("0"))
+
 	// test warnings
 	tk.MustQuery("select case when b=0 then 1 else 1/b end from t")
 	tk.MustQuery("show warnings").Check(testkit.Rows())

diff --git a/types/field_type.go b/types/field_type.go
@@ -133,8 +133,8 @@ func AggregateEvalType(fts []*FieldType, flag *uint) EvalType {
 		}
 		lft = rft
 	}
-	setTypeFlag(flag, mysql.UnsignedFlag, unsigned)
-	setTypeFlag(flag, mysql.BinaryFlag, !aggregatedEvalType.IsStringKind() || gotBinString)
+	SetTypeFlag(flag, mysql.UnsignedFlag, unsigned)
+	SetTypeFlag(flag, mysql.BinaryFlag, !aggregatedEvalType.IsStringKind() || gotBinString)
 	return aggregatedEvalType
 }
 
@@ -159,7 +159,8 @@ func mergeEvalType(lhs, rhs EvalType, lft, rft *FieldType, isLHSUnsigned, isRHSU
 	return ETInt
 }
 
-func setTypeFlag(flag *uint, flagItem uint, on bool) {
+// SetTypeFlag turns the flagItem on or off.
+func SetTypeFlag(flag *uint, flagItem uint, on bool) {
 	if on {
 		*flag |= flagItem
 	} else {