11.3.6. Fractional Seconds in Time Values

Before MySQL 5.6.4, the instances are limited in which a fractional seconds part is permitted in temporal values. A trailing fractional part is permissible in contexts such as literal values, and in the arguments to or return values from some temporal functions. Example:

mysql> SELECT MICROSECOND('2010-12-10
        14:12:09.019473');+-------------------------------------------+| MICROSECOND('2010-12-10 14:12:09.019473') |+-------------------------------------------+|                                     19473 |+-------------------------------------------+

However, when MySQL stores a value into a column of any temporal data type, it discards any fractional part and does not store it.

MySQL 5.6.4 and up expands fractional seconds support 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:
```
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.)
Functions that take temporal arguments accept values with fractional seconds. Return values from temporal functions include fractional seconds as appropriate. For example, NOW() with no argument returns the current date and time with no fractional part, but takes an optional argument from 0 to 6 to specify that the return value includes a fractional seconds part of that many digits.
Syntax for temporal literals produces temporal values: DATE 'str', TIME 'str', and TIMESTAMP 'str', and the ODBC-syntax equivalents. The resulting value includes a trailing fractional seconds part if specified. Previously, the temporal type keyword was ignored and these constructs produced the string value. See Standard SQL and ODBC Date and Time Literals

In some cases, previously accepted syntax may produce different results. The following items indicate where existing code may need to be changed to avoid problems:

Some expressions produce results that differ from previous results. Examples: The timestamp system variable returns a value that includes a microseconds fractional part rather than an integer. Functions that return a result that includes the current time (such as CURTIME(), SYSDATE(), or UTC_TIMESTAMP()) interpret an argument as an fsp value and the return value includes a fractional seconds part of that many digits. Previously, these functions permitted an argument but ignored it.
TIME values are converted to DATETIME by adding the time to the current date. (This means that the date part of the result differs from the current date if the time value is outside the range from '00:00:00' to '23:59:59'.) Previously, conversion of TIME values to DATETIME was unreliable. See Section 11.3.7, "Conversion Between Date and Time Types".
TIMESTAMP(N) was permitted in old MySQL versions, but N was a display width rather than fractional seconds precision. Support for this behavior was removed in MySQL 5.5.3, so applications that are reasonably up to date should not be subject to this issue. Otherwise, code must be rewritten.