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planner: the UNION's merge type should exclude the pure NULL #26561

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merged 2 commits into from
Jul 26, 2021
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planner: the UNION's merge type should exclude the pure NULL #26561

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4d899d8
planner: the UNION's merge type should exclude the pure NULL
winoros Jul 26, 2021
26416ee
Merge branch 'master' into issue26559
ti-chi-bot Jul 26, 2021
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8 changes: 8 additions & 0 deletions planner/core/integration_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -3996,3 +3996,11 @@ func (s *testIntegrationSerialSuite) TestIssue26214(c *C) {
_, err := tk.Exec("select * from t where case when a < 0 then 1 else 2 end <= 1 order by 4;")
c.Assert(core.ErrUnknownColumn.Equal(err), IsTrue)
}

func (s *testIntegrationSuite) TestIssue26559(c *C) {
tk := testkit.NewTestKit(c, s.store)
tk.MustExec("use test")
tk.MustExec("create table t(a timestamp, b datetime);")
tk.MustExec("insert into t values('2020-07-29 09:07:01', '2020-07-27 16:57:36');")
tk.MustQuery("select greatest(a, b) from t union select null;").Sort().Check(testkit.Rows("2020-07-29 09:07:01", "<nil>"))
}
6 changes: 6 additions & 0 deletions planner/core/logical_plan_builder.go
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Expand Up @@ -1324,6 +1324,12 @@ func (b *PlanBuilder) buildDistinct(child LogicalPlan, length int) (*LogicalAggr
// unionJoinFieldType finds the type which can carry the given types in Union.
// Note that unionJoinFieldType doesn't handle charset and collation, caller need to handle it by itself.
func unionJoinFieldType(a, b *types.FieldType) *types.FieldType {
// We ignore the pure NULL type.
if a.Tp == mysql.TypeNull {
return b
} else if b.Tp == mysql.TypeNull {
return a
}
resultTp := types.NewFieldType(types.MergeFieldType(a.Tp, b.Tp))
// This logic will be intelligible when it is associated with the buildProjection4Union logic.
if resultTp.Tp == mysql.TypeNewDecimal {
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