TIMESTAMP

Syntax

TIMESTAMP [(<microsecond precision)]

Description

A timestamp in the format YYYY-MM-DD HH:MM:SS.ffffff.

The timestamp field is generally used to define at which moment in time a row was added or updated and by default will automatically be assigned the current datetime when a record is inserted or updated. The automatic properties only apply to the first TIMESTAMP in the record; subsequent TIMESTAMP columns will not be changed.

MariaDB starting with 10.1.2

MariaDB 10.1.2 introduced the --mysql56-temporal-format option, on by default, which allows MariaDB to store TIMESTAMPs using the same low-level format MySQL 5.6 uses.

For more information, see Internal Format.

Supported Values

MariaDB stores values that use the TIMESTAMP data type as the number of seconds since '1970-01-01 00:00:00' (UTC). This means that the TIMESTAMP data type can hold values between '1970-01-01 00:00:01' (UTC) and '2038-01-19 03:14:07' (UTC).

MariaDB can also store microseconds with a precision between 0 and 6. If no microsecond precision is specified, then 0 is used by default.

Automatic Values

MariaDB has special behavior for the first column that uses the TIMESTAMP data type in a specific table. For the first column that uses the TIMESTAMP data type in a specific table, MariaDB automatically assigns the following properties to the column:

  • DEFAULT CURRENT_TIMESTAMP
  • ON UPDATE CURRENT_TIMESTAMP

This means that if the column is not explicitly assigned a value in an INSERT or UPDATE query, then MariaDB will automatically initialize the column's value with the current date and time.

This automatic initialization for INSERT and UPDATE queries can also be explicitly enabled for a column that uses the TIMESTAMP data type by specifying the DEFAULT CURRENT_TIMESTAMP and ON UPDATE CURRENT_TIMESTAMP clauses for the column. In these clauses, any synonym of CURRENT_TIMESTAMP is accepted, including CURRENT_TIMESTAMP(), NOW(), LOCALTIME, LOCALTIME(), LOCALTIMESTAMP, and LOCALTIMESTAMP().

This automatic initialization for INSERT queries can also be explicitly disabled for a column that uses the TIMESTAMP data type by specifying a constant DEFAULT value. For example, DEFAULT 0.

This automatic initialization for UPDATE queries can also be explicitly disabled for a column that uses the TIMESTAMP data type by specifying a DEFAULT clause for the column, but no ON UPDATE clause. If a DEFAULT clause is explicitly specified for a column that uses the TIMESTAMP data type, but an ON UPDATE clause is not specified for the column, then the timestamp value will not automatically change when an UPDATE statement is executed.

MariaDB also has special behavior if NULL is assigned to column that uses the TIMESTAMP data type. If the column is assigned the NULL value in an INSERT or UPDATE query, then MariaDB will automatically initialize the column's value with the current date and time. For details, see NULL values in MariaDB.

This automatic initialization for NULL values can also be explicitly disabled for a column that uses the TIMESTAMP data type by specifying the NULL attribute for the column. In this case, if the column's value is set to NULL, then the column's value will actually be set to NULL.

Time Zones

If a column uses the TIMESTAMP data type, then any inserted values are converted from the session's time zone to Coordinated Universal Time (UTC) when stored, and converted back to the session's time zone when retrieved.

MariaDB does not currently store any time zone identifier with the value of the TIMESTAMP data type. See MDEV-10018 for more information.

MariaDB does not currently support time zone literals that contain time zone identifiers. See MDEV-11829 for more information.

Limitations

  • Because the TIMESTAMP value is stored as Epoch Seconds, the timestamp value '1970-01-01 00:00:00' (UTC) is reserved since the second #0 is used to represent '0000-00-00 00:00:00'.
  • In MariaDB 5.5 and before there could only be one TIMESTAMP column per table that had CURRENT_TIMESTAMP defined as its default value. This limit has no longer applied since MariaDB 10.0.

SQL_MODE=MAXDB

If the SQL_MODE is set to MAXDB, TIMESTAMP fields will be silently converted to DATETIME.

Internal Format

In MariaDB 10.1.2 a new temporal format was introduced from MySQL 5.6 that alters how the TIME, DATETIME and TIMESTAMP columns operate at lower levels. These changes allow these temporal data types to have fractional parts and negative values. You can disable this feature using the mysql56_temporal_format system variable.

Tables that include TIMESTAMP values that were created on an older version of MariaDB or that were created while the mysql56_temporal_format system variable was disabled continue to store data using the older data type format.

In order to update table columns from the older format to the newer format, execute an ALTER TABLE... MODIFY COLUMN statement that changes the column to the *same* data type. This change may be needed if you want to export the table's tablespace and import it onto a server that has mysql56_temporal_format=ON set (see MDEV-15225).

For instance, if you have a TIMESTAMP column in your table:

SHOW VARIABLES LIKE 'mysql56_temporal_format';

+-------------------------+-------+
| Variable_name           | Value |
+-------------------------+-------+
| mysql56_temporal_format | ON    |
+-------------------------+-------+

ALTER TABLE example_table MODIFY ts_col TIMESTAMP;

When MariaDB executes the ALTER TABLE statement, it converts the data from the older temporal format to the newer one.

In the event that you have several tables and columns using temporal data types that you want to switch over to the new format, make sure the system variable is enabled, then perform a dump and restore using mysqldump. The columns using relevant temporal data types are restored using the new temporal format.

Note: Prior to MySQL 4.1 a different format for the TIMESTAMP datatype was used. This format is unsupported in MariaDB 5.1 and upwards.

Examples

CREATE TABLE t (id INT, ts TIMESTAMP);

DESC t;
+-------+-----------+------+-----+-------------------+-----------------------------+
| Field | Type      | Null | Key | Default           | Extra                       |
+-------+-----------+------+-----+-------------------+-----------------------------+
| id    | int(11)   | YES  |     | NULL              |                             |
| ts    | timestamp | NO   |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
+-------+-----------+------+-----+-------------------+-----------------------------+

INSERT INTO t(id)  VALUES (1),(2);

SELECT * FROM t;
+------+---------------------+
| id   | ts                  |
+------+---------------------+
|    1 | 2013-07-22 12:50:05 |
|    2 | 2013-07-22 12:50:05 |
+------+---------------------+

INSERT INTO t  VALUES (3,NULL),(4,'2001-07-22 12:12:12');

SELECT * FROM t;
+------+---------------------+
| id   | ts                  |
+------+---------------------+
|    1 | 2013-07-22 12:50:05 |
|    2 | 2013-07-22 12:50:05 |
|    3 | 2013-07-22 12:51:56 |
|    4 | 2001-07-22 12:12:12 |
+------+---------------------+

Converting to Unix epoch:

SELECT ts, UNIX_TIMESTAMP(ts) FROM t;
+---------------------+--------------------+
| ts                  | UNIX_TIMESTAMP(ts) |
+---------------------+--------------------+
| 2013-07-22 12:50:05 |         1374490205 |
| 2013-07-22 12:50:05 |         1374490205 |
| 2013-07-22 12:51:56 |         1374490316 |
| 2001-07-22 12:12:12 |          995796732 |
+---------------------+--------------------+

Update also changes the timestamp:

UPDATE t set id=5 WHERE id=1;

SELECT * FROM t;
+------+---------------------+
| id   | ts                  |
+------+---------------------+
|    5 | 2013-07-22 14:52:33 |
|    2 | 2013-07-22 12:50:05 |
|    3 | 2013-07-22 12:51:56 |
|    4 | 2001-07-22 12:12:12 |
+------+---------------------+

Default NULL:

CREATE TABLE t2 (id INT, ts TIMESTAMP NULL ON UPDATE CURRENT_TIMESTAMP);

INSERT INTO t(id)  VALUES (1),(2);

SELECT * FROM t2;

INSERT INTO t2(id)  VALUES (1),(2);

SELECT * FROM t2;
+------+------+
| id   | ts   |
+------+------+
|    1 | NULL |
|    2 | NULL |
+------+------+

UPDATE t2 SET id=3 WHERE id=1;

SELECT * FROM t2;
+------+---------------------+
| id   | ts                  |
+------+---------------------+
|    3 | 2013-07-22 15:32:22 |
|    2 | NULL                |
+------+---------------------+

Only the first timestamp is automatically inserted and updated:

CREATE TABLE t3 (id INT, ts1 TIMESTAMP, ts2 TIMESTAMP);

INSERT INTO t3(id)  VALUES (1),(2);

SELECT * FROM t3;
+------+---------------------+---------------------+
| id   | ts1                 | ts2                 |
+------+---------------------+---------------------+
|    1 | 2013-07-22 15:35:07 | 0000-00-00 00:00:00 |
|    2 | 2013-07-22 15:35:07 | 0000-00-00 00:00:00 |
+------+---------------------+---------------------+

DESC t3;
+-------+-----------+------+-----+---------------------+-----------------------------+
| Field | Type      | Null | Key | Default             | Extra                       |
+-------+-----------+------+-----+---------------------+-----------------------------+
| id    | int(11)   | YES  |     | NULL                |                             |
| ts1   | timestamp | NO   |     | CURRENT_TIMESTAMP   | on update CURRENT_TIMESTAMP |
| ts2   | timestamp | NO   |     | 0000-00-00 00:00:00 |                             |
+-------+-----------+------+-----+---------------------+-----------------------------+

Explicitly setting a timestamp with the CURRENT_TIMESTAMP function:

INSERT INTO t3(id,ts2)  VALUES (3,CURRENT_TIMESTAMP());

SELECT * FROM t3;
+------+---------------------+---------------------+
| id   | ts1                 | ts2                 |
+------+---------------------+---------------------+
|    1 | 2013-07-22 15:35:07 | 0000-00-00 00:00:00 |
|    2 | 2013-07-22 15:35:07 | 0000-00-00 00:00:00 |
|    3 | 2013-07-22 15:38:52 | 2013-07-22 15:38:52 |
+------+---------------------+---------------------+

Specifying the timestamp as NOT NULL:

CREATE TABLE t4 (id INT, ts TIMESTAMP NOT NULL);

INSERT INTO t4(id)  VALUES (1);
SELECT SLEEP(1);
INSERT INTO t4(id,ts) VALUES (2,NULL);

SELECT * FROM t4;

See Also

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