DATE()

    2. > create table t1(a date, b datetime);
    3. > insert into t1 values('2022-01-01','2022-01-01 01:01:01');
    4. > insert into t1 values('2022-01-01','2022-01-01 01:01:01');
    5. > insert into t1 values(20220101,'2022-01-01 01:01:01');
    6. > insert into t1 values('2022-01-02','2022-01-02 23:01:01');
    7. > insert into t1 values('2022-06-30','2021-12-30 23:59:59');
    8. > select date(a),date(b) from t1;
    9. +------------+------------+
    11. +------------+------------+
    12. | 2022-01-01 | 2022-01-01 |
    13. | 2022-01-01 | 2022-01-01 |
    14. | 2022-01-01 | 2022-01-01 |
    15. | 2022-01-02 | 2022-01-02 |
    16. | 2021-12-31 | 2021-12-30 |
    17. | 2022-06-30 | 2021-12-30 |
    18. > select date(a),date(date(a)) as dda from t1;
    20. | date(a)    | dda        |
    21. +------------+------------+
    22. | 2022-01-01 | 2022-01-01 |
    23. | 2022-01-01 | 2022-01-01 |
    24. | 2022-01-01 | 2022-01-01 |
    25. | 2022-01-02 | 2022-01-02 |
    26. | 2021-12-31 | 2021-12-31 |
    27. | 2022-06-30 | 2022-06-30 |
    28. +------------+------------+