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11.1.2 Date and Time Type Overview

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A summary of the temporal data types follows. For additional information about properties and storage requirements of the temporal types, see Section 11.3, “Date and Time Types”, and Section 11.8, “Data Type Storage Requirements”. For descriptions of functions that operate on temporal values, see Section 12.7, “Date and Time Functions”.

For the DATE and DATETIME range descriptions, “supported” means that although earlier values might work, there is no guarantee.

MySQL permits fractional seconds for TIME, DATETIME, and TIMESTAMP values, with up to microseconds (6 digits) precision. To define a column that includes a fractional seconds part, use the syntax type_name(fsp), where type_name is TIME, DATETIME, or TIMESTAMP, and fsp is the fractional seconds precision. For example:

  1. CREATE TABLE t1 (t TIME(3), dt DATETIME(6));

The fsp value, if given, must be in the range 0 to 6. A value of 0 signifies that there is no fractional part. If omitted, the default precision is 0. (This differs from the standard SQL default of 6, for compatibility with previous MySQL versions.)

Any TIMESTAMP or DATETIME column in a table can have automatic initialization and updating properties.

  • DATE

    A date. The supported range is '1000-01-01' to '9999-12-31'. MySQL displays DATE values in 'YYYY-MM-DD' format, but permits assignment of values to DATE columns using either strings or numbers.

  • DATETIME[(fsp)]

    A date and time combination. The supported range is '1000-01-01 00:00:00.000000' to '9999-12-31 23:59:59.999999'. MySQL displays DATETIME values in 'YYYY-MM-DD hh:mm:ss[.fraction]' format, but permits assignment of values to DATETIME columns using either strings or numbers.

    An optional fsp value in the range from 0 to 6 may be given to specify fractional seconds precision. A value of 0 signifies that there is no fractional part. If omitted, the default precision is 0.

    Automatic initialization and updating to the current date and time for DATETIME columns can be specified using DEFAULT and ON UPDATE column definition clauses, as described in Section 11.3.4, “Automatic Initialization and Updating for TIMESTAMP and DATETIME”.

  • TIMESTAMP[(fsp)]

    A timestamp. The range is '1970-01-01 00:00:01.000000' UTC to '2038-01-19 03:14:07.999999' UTC. TIMESTAMP values are stored as the number of seconds since the epoch ('1970-01-01 00:00:00' UTC). A TIMESTAMP cannot represent the value '1970-01-01 00:00:00' because that is equivalent to 0 seconds from the epoch and the value 0 is reserved for representing '0000-00-00 00:00:00', the “zero” TIMESTAMP value.

    An optional fsp value in the range from 0 to 6 may be given to specify fractional seconds precision. A value of 0 signifies that there is no fractional part. If omitted, the default precision is 0.

    The way the server handles TIMESTAMP definitions depends on the value of the explicit_defaults_for_timestamp system variable (see Section 5.1.8, “Server System Variables”).

    If explicit_defaults_for_timestamp is enabled, there is no automatic assignment of the DEFAULT CURRENT_TIMESTAMP or ON UPDATE CURRENT_TIMESTAMP attributes to any TIMESTAMP column. They must be included explicitly in the column definition. Also, any TIMESTAMP not explicitly declared as NOT NULL permits NULL values.

    If explicit_defaults_for_timestamp is disabled, the server handles TIMESTAMP as follows:

    Unless specified otherwise, the first TIMESTAMP column in a table is defined to be automatically set to the date and time of the most recent modification if not explicitly assigned a value. This makes TIMESTAMP useful for recording the timestamp of an INSERT or UPDATE operation. You can also set any TIMESTAMP column to the current date and time by assigning it a NULL value, unless it has been defined with the NULL attribute to permit NULL values.

    Automatic initialization and updating to the current date and time can be specified using DEFAULT CURRENT_TIMESTAMP and ON UPDATE CURRENT_TIMESTAMP column definition clauses. By default, the first TIMESTAMP column has these properties, as previously noted. However, any TIMESTAMP column in a table can be defined to have these properties.

  • TIME[(fsp)]

    A time. The range is '-838:59:59.000000' to '838:59:59.000000'. MySQL displays TIME values in 'hh:mm:ss[.fraction]' format, but permits assignment of values to TIME columns using either strings or numbers.

    An optional fsp value in the range from 0 to 6 may be given to specify fractional seconds precision. A value of 0 signifies that there is no fractional part. If omitted, the default precision is 0.

  • YEAR[(4)]

    A year in four-digit format. MySQL displays YEAR values in YYYY format, but permits assignment of values to YEAR columns using either strings or numbers. Values display as 1901 to 2155, and 0000.

    For additional information about YEAR display format and interpretation of input values, see Section 11.3.3, “The YEAR Type”.

    Note

    MySQL 8.0 does not support the YEAR(2) data type permitted in older versions of MySQL. For instructions on converting to YEAR(4), see YEAR(2) Limitations and Migrating to YEAR(4) in MySQL 5.7 Reference Manual.

The SUM() and AVG() aggregate functions do not work with temporal values. (They convert the values to numbers, losing everything after the first nonnumeric character.) To work around this problem, convert to numeric units, perform the aggregate operation, and convert back to a temporal value. Examples:

  1. SELECT SEC_TO_TIME(SUM(TIME_TO_SEC(time_col))) FROM tbl_name;
  2. SELECT FROM_DAYS(SUM(TO_DAYS(date_col))) FROM tbl_name;

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Dokument erstellt 26/06/2006, zuletzt geändert 26/10/2018
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