Same agg func in one sql will gets different result

[wshwsh12]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

use test;
drop table if exists t1;
create table t1 (c_int int not null);
insert into t1 values (1), (2), (3),(1),(2),(3);
drop table if exists t2;
create table t2 (c_int int not null);
insert into t2 values (1), (2), (3),(1),(2),(3);

select 
(select count(distinct c_int) from t2 where c_int >= t1.c_int) c1, 
(select count(distinct c_int) from t2 where c_int >= t1.c_int) c2
from t1 group by c_int;

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

+------+------+
| c1   | c2   |
+------+------+
|    3 |    3 |
|    2 |    2 |
|    1 |    1 |
+------+------+
3 rows in set (0.001 sec)

3. What did you see instead (Required)

+----+----+
| c1 | c2 |
+----+----+
|  4 |  2 |
|  6 |  3 |
|  2 |  1 |
+----+----+
3 rows in set (0.004 sec)

4. What is your TiDB version? (Required)

v4.0, v5.0, v5.1, master

[wshwsh12]

Only select one column will also gets wrong reuslt.

[tidb]> select 
    -> (select count(distinct c_int) from t2 where c_int >= t1.c_int) c1
    -> from t1 group by c_int;
+----+
| c1 |
+----+
|  6 |
|  2 |
|  4 |
+----+
3 rows in set (0.001 sec)

See the expaln and find the dinstct flag is missing:

[tidb]> desc select  (select count(distinct c_int) from t2 where c_int >= t1.c_int) c1 from t1 group by c_int;
+--------------------------------+-------------+-----------+---------------+------------------------------------------------------------------------+
| id                             | estRows     | task      | access object | operator info                                                          |
+--------------------------------+-------------+-----------+---------------+------------------------------------------------------------------------+
| HashAgg_12                     | 8000.00     | root      |               | group by:test.t1.c_int, funcs:count(test.t2.c_int)->Column#7           |
| └─HashJoin_14                  | 80000000.00 | root      |               | CARTESIAN left outer join, other cond:ge(test.t2.c_int, test.t1.c_int) |
|   ├─HashAgg_17(Build)          | 8000.00     | root      |               | group by:test.t1.c_int, funcs:firstrow(test.t1.c_int)->test.t1.c_int   |
|   │ └─TableReader_22           | 10000.00    | root      |               | data:TableFullScan_21                                                  |
|   │   └─TableFullScan_21       | 10000.00    | cop[tikv] | table:t1      | keep order:false, stats:pseudo                                         |
|   └─TableReader_24(Probe)      | 10000.00    | root      |               | data:TableFullScan_23                                                  |
|     └─TableFullScan_23         | 10000.00    | cop[tikv] | table:t2      | keep order:false, stats:pseudo                                         |
+--------------------------------+-------------+-----------+---------------+------------------------------------------------------------------------+
7 rows in set (0.001 sec)

[ti-srebot]

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