query result cache with timezone maybe confusing

[TCeason]

Look this example:

:) SET global  enable_query_result_cache = 1;

:) create table t(c1 timestamp);

:) insert into t values('2017-12-01 22:46:53.000000'), ('2017-12-02 22:46:53.000000');

:) select c1, to_date(c1) from t;


┌──────────────────────────────────────┐
│          c1         │   to_date(c1)  │
│ Nullable(Timestamp) │ Nullable(Date) │
├─────────────────────┼────────────────┤
│ 2017-12-01 22:46:53 │ 2017-12-01     │
│ 2017-12-02 22:46:53 │ 2017-12-02     │
└──────────────────────────────────────┘
2 rows read in 0.109 sec. Processed 2 rows, 17 B (18.39 rows/s, 156 B/s)

:) set timezone='Asia/Shanghai';


0 row read in 0.014 sec. Processed 0 row, 0 B (0 row/s, 0 B/s)

:) select c1, to_date(c1) from t;


┌──────────────────────────────────────┐
│          c1         │   to_date(c1)  │
│ Nullable(Timestamp) │ Nullable(Date) │
├─────────────────────┼────────────────┤
│ 2017-12-02 06:46:53 │ 2017-12-01     │
│ 2017-12-03 06:46:53 │ 2017-12-02     │
└──────────────────────────────────────┘
2 rows read in 0.039 sec. Processed 0 rows, 0 B (0 rows/s, 0 B/s)

The to_date is string, the c1 is ts and when written as a result, ts adapts to the current time zone, but to_date will return the value in cache.

So, it cause this result:

│ 2017-12-02 06:46:53 │ 2017-12-01     │
│ 2017-12-03 06:46:53 │ 2017-12-02     │

[TCeason]

If you are trying to detect the problem, explain this sql is the best way for now.