yiguolei commented on code in PR #998:
URL: https://github.com/apache/doris-website/pull/998#discussion_r1716279274
##########
docs/sql-manual/sql-data-types/date-time/datetime-overview.md:
##########
@@ -24,11 +24,46 @@ specific language governing permissions and limitations
under the License.
-->
+### Description
+Date types include DATE, TIME and DATETIME, DATE type only stores the date
accurate to the day, DATETIME type stores the date and time, which can be
accurate to microseconds. TIME type only stores the time, and **does not
support the construction of the table storage for the time being, can only be
used in the query process**.
+### Calculation and Type Convertion
-The date data types include DATE and DATETIME:
+When performing mathematical calculations on a date type, the date type will
be converted to the corresponding numeric type (e.g. BIGINT, DOUBLE, etc.). The
conversion is similar to number splicing, see the example below:
-- **[DATE](../datetime/DATE.md)**: It stores only the date. The minimum
precision unit is days.
+```sql
+mysql> select cast('2020-12-12' as date)*1;
++----------------------------------------------------+
+| (cast(cast('2020-12-12' as DATEV2) as BIGINT) * 1) |
++----------------------------------------------------+
+| 20201212 |
++----------------------------------------------------+
+1 row in set (0.12 sec)
-- **[DATETIME](../datetime/DATETIME.md)**: It stores both the date and time.
The minimum precision unit is milliseconds.
\ No newline at end of file
+mysql> select cast('2020-12-12 05:10:32.123456' as datetime(6))*1;
++---------------------------------------------------------------------------+
+| (cast(cast('2020-12-12 05:10:32.123456' as DATETIMEV2(6)) as BIGINT) * 1) |
++---------------------------------------------------------------------------+
+| 20201212051032 |
Review Comment:
也就是说 datetime 类型cast 到int的时候是保留到秒？
我们得有这个测试，确保这个行为不发生变化
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