[Bug]: count(distinct c1) returns wrong result

[qinling0210]

Is there an existing issue for the same bug?

• I have checked the existing issues.

Version or Commit ID

v0.6.15

Other environment information

Actual behavior and How to reproduce it

create table t1(c1 int);
insert into t1 values (1),(2),(3),(1),(2),(3);

select count(c1) from t1;

 count(c1) 
-----------
         6
(1 row)

select count(distinct c1) from t1;

 count(c1) 
-----------
         6
(1 row)

"select count(distinct c1) from t1" should return 3

Expected behavior

No response

Additional information

No response