Datetime 

Allows to store an instant in time, that can be expressed as a calendar date and a time of a day.

Syntax:

DateTime([timezone])

Supported range of values: [1970-01-01 00:00:00, 2105-12-31 23:59:59].

Resolution: 1 second.

Usage Remarks 

The point in time is saved as a Unix timestamp, regardless of the time zone or daylight saving time. Additionally, the DateTime type can store time zone that is the same for the entire column, that affects how the values of the DateTime type values are displayed in text format and how the values specified as strings are parsed (‘2020-01-01 05:00:01’). The time zone is not stored in the rows of the table (or in resultset), but is stored in the column metadata.
A list of supported time zones can be found in the IANA Time Zone Database.
The tzdata package, containing IANA Time Zone Database, should be installed in the system. Use the timedatectl list-timezones command to list timezones known by a local system.

You can explicitly set a time zone for DateTime-type columns when creating a table. If the time zone isn’t set, ClickHouse uses the value of the timezone parameter in the server settings or the operating system settings at the moment of the ClickHouse server start.

The clickhouse-client applies the server time zone by default if a time zone isn’t explicitly set when initializing the data type. To use the client time zone, run clickhouse-client with the --use_client_time_zone parameter.

ClickHouse outputs values in YYYY-MM-DD hh:mm:ss text format by default. You can change the output with the formatDateTime function.

When inserting data into ClickHouse, you can use different formats of date and time strings, depending on the value of the date_time_input_format setting.

Examples 

1. Creating a table with a DateTime-type column and inserting data into it:

CREATE TABLE dt
(
    `timestamp` DateTime('Europe/Moscow'),
    `event_id` UInt8
)
ENGINE = TinyLog;
INSERT INTO dt Values (1546300800, 1), ('2019-01-01 00:00:00', 2);
SELECT * FROM dt;
┌───────────timestamp─┬─event_id─┐
│ 2019-01-01 03:00:00 │        1 │
│ 2019-01-01 00:00:00 │        2 │
└─────────────────────┴──────────┘
  • When inserting datetime as an integer, it is treated as Unix Timestamp (UTC). 1546300800 represents '2019-01-01 00:00:00' UTC. However, as timestamp column has Europe/Moscow (UTC+3) timezone specified, when outputting as string the value will be shown as '2019-01-01 03:00:00'
  • When inserting string value as datetime, it is treated as being in column timezone. '2019-01-01 00:00:00' will be treated as being in Europe/Moscow timezone and saved as 1546290000.

2. Filtering on DateTime values

SELECT * FROM dt WHERE timestamp = toDateTime('2019-01-01 00:00:00', 'Europe/Moscow')
┌───────────timestamp─┬─event_id─┐
│ 2019-01-01 00:00:00 │        2 │
└─────────────────────┴──────────┘

DateTime column values can be filtered using a string value in WHERE predicate. It will be converted to DateTime automatically:

SELECT * FROM dt WHERE timestamp = '2019-01-01 00:00:00'
┌───────────timestamp─┬─event_id─┐
│ 2019-01-01 03:00:00 │        1 │
└─────────────────────┴──────────┘

3. Getting a time zone for a DateTime-type column:

SELECT toDateTime(now(), 'Europe/Moscow') AS column, toTypeName(column) AS x
┌──────────────column─┬─x─────────────────────────┐
│ 2019-10-16 04:12:04 │ DateTime('Europe/Moscow') │
└─────────────────────┴───────────────────────────┘

4. Timezone conversion

SELECT
toDateTime(timestamp, 'Europe/London') as lon_time,
toDateTime(timestamp, 'Europe/Moscow') as mos_time
FROM dt
┌───────────lon_time──┬────────────mos_time─┐
│ 2019-01-01 00:00:00 │ 2019-01-01 03:00:00 │
│ 2018-12-31 21:00:00 │ 2019-01-01 00:00:00 │
└─────────────────────┴─────────────────────┘

See Also 

Rating: 5 - 2 votes

Was this content helpful?
★★★★★