CastTimeAsReal was pushed down to tiflash by mistake

[wshwsh12]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

CastTimeAsReal shouldn't push down to tiflash, because CastTimeAsReal is not supported in tiflash.

use test;
drop table t;
create table t(a timestamp);
insert into t values("2020-10-10 10:10:10");
alter table t set tiflash replica 1;

[tidb]> desc select avg(a) from t;
+--------------------------------+----------+-------------------+---------------+------------------------------------------------------------------+
| id                             | estRows  | task              | access object | operator info                                                    |
+--------------------------------+----------+-------------------+---------------+------------------------------------------------------------------+
| HashAgg_20                     | 1.00     | root              |               | funcs:avg(Column#6, Column#7)->Column#3                          |
| └─TableReader_22               | 1.00     | root              |               | data:ExchangeSender_21                                           |
|   └─ExchangeSender_21          | 1.00     | batchCop[tiflash] |               | ExchangeType: PassThrough                                        |
|     └─HashAgg_8                | 1.00     | batchCop[tiflash] |               | funcs:count(Column#10)->Column#6, funcs:sum(Column#11)->Column#7 |
|       └─Projection_31          | 10000.00 | batchCop[tiflash] |               | test.t2.a, cast(test.t2.a, double(23,4) BINARY)->Column#11       |
|         └─TableFullScan_19     | 10000.00 | batchCop[tiflash] | table:t2      | keep order:false, stats:pseudo                                   |
+--------------------------------+----------+-------------------+---------------+------------------------------------------------------------------+
6 rows in set (0.001 sec)
[tidb]>  select avg(a) from t;
ERROR 1105 (HY000): other error for mpp stream: DB::TiFlashException: CastTimeAsReal is not supported.

But, we can see the push down list in tidb.

tidb/expression/expression.go

Lines 1057 to 1060 in 5cc6b81

	case tipb.ScalarFuncSig_CastIntAsReal, tipb.ScalarFuncSig_CastRealAsReal, tipb.ScalarFuncSig_CastStringAsReal: /*, tipb.ScalarFuncSig_CastDecimalAsReal,
	tipb.ScalarFuncSig_CastDurationAsReal, tipb.ScalarFuncSig_CastTimeAsReal, tipb.ScalarFuncSig_CastJsonAsReal*/
	// TiFlash cast only support cast to Float64 or the source type is the same as the target type
	return sourceType.Tp == retType.Tp || retType.Tp == mysql.TypeDouble

CastTimeAsReal is commented out.

2. What did you expect to see? (Required)

Run successfully.

3. What did you see instead (Required)

Failed.

4. What is your TiDB version? (Required)

master(e8f4e47)

[fuzhe1989]

/assign @wshwsh12

[wshwsh12]

Fixed by #29274

[fuzhe1989]

@wshwsh12 guess we still need to fix the issue since the plan is unexpected.