Suspicious result when aggregating on volatile functions

[fixdb]

Bug Report

create table foo(a int, b int, c int, d int);
insert into foo values(1,1,1,10),(2,2,2,2);
insert into foo values(3,1,1,10),(3,2,2,2);

explain select b*floor(2*rand()) as e,  count(d) from foo group by e;
+-----------------------------+---------+--------------+---------------+------------------------------------------------------------------------------------------------+
| id                          | estRows | task         | access object | operator info                                                                                  |
+-----------------------------+---------+--------------+---------------+------------------------------------------------------------------------------------------------+
| Projection_4                | 3.20    | root         |               | mul(cast(test.foo.b, double BINARY), floor(mul(2, rand())))->Column#7, Column#6                |
| └─HashAgg_5                 | 3.20    | root         |               | group by:Column#11, funcs:count(Column#9)->Column#6, funcs:firstrow(Column#10)->test.foo.b     |
|   └─Projection_15           | 4.00    | root         |               | test.foo.d, test.foo.b, mul(cast(test.foo.b, double BINARY), floor(mul(2, rand())))->Column#11 |
|     └─TableReader_10        | 4.00    | root         |               | data:TableFullScan_9                                                                           |
|       └─TableFullScan_9     | 4.00    | cop[tiflash] | table:foo     | keep order:false, stats:pseudo                                                                 |
+-----------------------------+---------+--------------+---------------+------------------------------------------------------------------------------------------------+
5 rows in set, 4 warnings (0.00 sec)

-- sometimes I see this kind of suspicious result
select b*floor(2*rand()) as e,  count(d) from foo group by e;
+------+----------+
| e    | count(d) |
+------+----------+
|    2 |        1 |
|    2 |        1 |
|    0 |        2 |
+------+----------+
3 rows in set (0.02 sec)

Shouldn't each aggregate key only appear once?

I think the culprit may be we do the project again after the HashAgg. Each time rand() will generate different values.

[chrysan]

May be duplicated with #37986

[fixdb]

Not duplicate with https://github.com/pingcap/tidb/issues/37986, this issue still exists.