CURRENT_TIMESTAMP (Transact-SQL)
Эта функция возвращает текущую системную метку времени базы данных в виде значения datetime без смещения часового пояса базы данных. CURRENT_TIMESTAMP наследует это значение от операционной системы компьютера, на котором работает экземпляр SQL Server.
Эта функция ANSI SQL эквивалентна функции GETDATE.
Обзор всех типов данных и функций даты и времени в языке Transact-SQL см. в статье Типы данных и функции даты и времени.
Синтаксические обозначения в Transact-SQL
Синтаксис
Ссылки на описание синтаксиса Transact-SQL для SQL Server 2014 и более ранних версий, см. в статье Документация по предыдущим версиям.
Аргументы
Эта функция не имеет аргументов.
Тип возвращаемых данных
datetime
Remarks
Функция CURRENT_TIMESTAMP может использоваться в инструкциях Transact-SQL везде, где допустимо использование выражения datetime.
CURRENT_TIMESTAMP является недетерминированной функцией. Невозможно проиндексировать представления и выражения, ссылающиеся на этот столбец.
Примеры
В приведенных ниже примерах с помощью шести системных функций SQL Server, которые возвращают текущую дату и время, возвращается дата, время или дата и время. Значения возвращаются последовательно, поэтому могут различаться на доли секунды. Обратите внимание на то, что возвращаемые значения будут соответствовать фактическим дню и времени выполнения.
Current timestamp mysql что это
This section describes the functions that can be used to manipulate temporal values. See Section 11.2, “Date and Time Data Types”, for a description of the range of values each date and time type has and the valid formats in which values may be specified.
Table 12.11 Date and Time Functions
Here is an example that uses date functions. The following query selects all rows with a date_col value from within the last 30 days:
The query also selects rows with dates that lie in the future.
Functions that expect date values usually accept datetime values and ignore the time part. Functions that expect time values usually accept datetime values and ignore the date part.
Other functions expect complete dates and return NULL for incomplete dates. These include functions that perform date arithmetic or that map parts of dates to names. For example:
ADDTIME() adds expr2 to expr1 and returns the result. expr1 is a time or datetime expression, and expr2 is a time expression.
Beginning with MySQL 8.0.28, the return type of this function and of the SUBTIME() function is determined as follows:
Otherwise, the resolved type of the function is derived from the resolved type of the first argument.
CONVERT_TZ() converts a datetime value dt from the time zone given by from_tz to the time zone given by to_tz and returns the resulting value. Time zones are specified as described in Section 5.1.15, “MySQL Server Time Zone Support”. This function returns NULL if the arguments are invalid.
On 32-bit platforms, the supported range of values for this function is the same as for the TIMESTAMP type (see Section 11.2.1, “Date and Time Data Type Syntax”, for range information). On 64-bit platforms, beginning with MySQL 8.0.28, the maximum supported value is ‘3001-01-18 23:59:59.999999’ UTC.
Regardless of platform or MySQL version, if the value falls out of the supported range when converted from from_tz to UTC, no conversion occurs.
Returns the current date as a value in ‘ YYYY-MM-DD ‘ or YYYYMMDD format, depending on whether the function is used in string or numeric context.
Current timestamp mysql что это
TIMESTAMP and DATETIME columns can be automatically initializated and updated to the current date and time (that is, the current timestamp).
For any TIMESTAMP or DATETIME column in a table, you can assign the current timestamp as the default value, the auto-update value, or both:
An auto-initialized column is set to the current timestamp for inserted rows that specify no value for the column.
An auto-updated column is automatically updated to the current timestamp when the value of any other column in the row is changed from its current value. An auto-updated column remains unchanged if all other columns are set to their current values. To prevent an auto-updated column from updating when other columns change, explicitly set it to its current value. To update an auto-updated column even when other columns do not change, explicitly set it to the value it should have (for example, set it to CURRENT_TIMESTAMP ).
In addition, if the explicit_defaults_for_timestamp system variable is disabled, you can initialize or update any TIMESTAMP (but not DATETIME ) 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.
TIMESTAMP or DATETIME column definitions can specify the current timestamp for both the default and auto-update values, for one but not the other, or for neither. Different columns can have different combinations of automatic properties. The following rules describe the possibilities:
With a DEFAULT clause but no ON UPDATE CURRENT_TIMESTAMP clause, the column has the given default value and is not automatically updated to the current timestamp.
With a constant, the default is the given value. In this case, the column has no automatic properties at all.
With an ON UPDATE CURRENT_TIMESTAMP clause and a constant DEFAULT clause, the column is automatically updated to the current timestamp and has the given constant default value.
With an ON UPDATE CURRENT_TIMESTAMP clause but no DEFAULT clause, the column is automatically updated to the current timestamp but does not have the current timestamp for its default value.
DATETIME has a default of NULL unless defined with the NOT NULL attribute, in which case the default is 0.
TIMESTAMP and DATETIME columns have no automatic properties unless they are specified explicitly, with this exception: If the explicit_defaults_for_timestamp system variable is disabled, the first TIMESTAMP column has both DEFAULT CURRENT_TIMESTAMP and ON UPDATE CURRENT_TIMESTAMP if neither is specified explicitly. To suppress automatic properties for the first TIMESTAMP column, use one of these strategies:
Enable the explicit_defaults_for_timestamp system variable. In this case, the DEFAULT CURRENT_TIMESTAMP and ON UPDATE CURRENT_TIMESTAMP clauses that specify automatic initialization and updating are available, but are not assigned to any TIMESTAMP column unless explicitly included in the column definition.
Alternatively, if explicit_defaults_for_timestamp is disabled, do either of the following:
Define the column with a DEFAULT clause that specifies a constant default value.
Consider these table definitions:
The tables have these properties:
In each table definition, the first TIMESTAMP column has no automatic initialization or updating.
If a TIMESTAMP or DATETIME column definition includes an explicit fractional seconds precision value anywhere, the same value must be used throughout the column definition. This is permitted:
This is not permitted:
TIMESTAMP Initialization and the NULL Attribute
The following table contains several TIMESTAMP columns that permit NULL values:
A TIMESTAMP column that permits NULL values does not take on the current timestamp at insert time except under one of the following conditions:
Its default value is defined as CURRENT_TIMESTAMP and no value is specified for the column
CURRENT_TIMESTAMP or any of its synonyms such as NOW() is explicitly inserted into the column
In other words, a TIMESTAMP column defined to permit NULL values auto-initializes only if its definition includes DEFAULT CURRENT_TIMESTAMP :
To set the TIMESTAMP column in either table to the current timestamp at insert time, explicitly assign it that value. For example:
Current timestamp mysql что это
This section describes the functions that can be used to manipulate temporal values. See Section 11.2, “Date and Time Data Types”, for a description of the range of values each date and time type has and the valid formats in which values may be specified.
Table 12.11 Date and Time Functions
Here is an example that uses date functions. The following query selects all rows with a date_col value from within the last 30 days:
The query also selects rows with dates that lie in the future.
Functions that expect date values usually accept datetime values and ignore the time part. Functions that expect time values usually accept datetime values and ignore the date part.
Other functions expect complete dates and return NULL for incomplete dates. These include functions that perform date arithmetic or that map parts of dates to names. For example:
ADDTIME() adds expr2 to expr1 and returns the result. expr1 is a time or datetime expression, and expr2 is a time expression.
CONVERT_TZ() converts a datetime value dt from the time zone given by from_tz to the time zone given by to_tz and returns the resulting value. Time zones are specified as described in Section 5.1.13, “MySQL Server Time Zone Support”. This function returns NULL if the arguments are invalid.
If the value falls out of the supported range of the TIMESTAMP type when converted from from_tz to UTC, no conversion occurs. The TIMESTAMP range is described in Section 11.2.1, “Date and Time Data Type Syntax”.
Returns the current date as a value in ‘ YYYY-MM-DD ‘ or YYYYMMDD format, depending on whether the function is used in string or numeric context.
Current timestamp mysql что это
MySQL 5.7 Reference Manual Including MySQL NDB Cluster 7.5 and NDB Cluster 7.6
12.7В Date and Time Functions
This section describes the functions that can be used to manipulate temporal values. See Section 11.2, “Date and Time Data Types”, for a description of the range of values each date and time type has and the valid formats in which values may be specified.
TableВ 12.11В Date and Time Functions
Here is an example that uses date functions. The following query selects all rows with a date_col value from within the last 30 days:
The query also selects rows with dates that lie in the future.
Functions that expect date values usually accept datetime values and ignore the time part. Functions that expect time values usually accept datetime values and ignore the date part.
Other functions expect complete dates and return NULL for incomplete dates. These include functions that perform date arithmetic or that map parts of dates to names. For example:
ADDTIME() adds expr2 to expr1 and returns the result. expr1 is a time or datetime expression, and expr2 is a time expression.
CONVERT_TZ() converts a datetime value dt from the time zone given by from_tz to the time zone given by to_tz and returns the resulting value. Time zones are specified as described in Section 5.1.13, “MySQL Server Time Zone Support”. This function returns NULL if the arguments are invalid.
If the value falls out of the supported range of the TIMESTAMP type when converted from from_tz to UTC, no conversion occurs. The TIMESTAMP range is described in Section 11.2.1, “Date and Time Data Type Syntax”.
Returns the current date as a value in ‘ YYYY-MM-DD ‘ or YYYYMMDD format, depending on whether the function is used in string or numeric context.
