13.2.6 时间值中的小数秒
MySQL has 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
, wheretype_name
(fsp
)type_name
isTIME
,DATETIME
, orTIMESTAMP
, andfsp
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.) -
Inserting a
TIME
,DATE
, orTIMESTAMP
value with a fractional seconds part into a column of the same type but having fewer fractional digits results in rounding. Consider a table created and populated as follows:CREATE TABLE fractest( c1 TIME(2), c2 DATETIME(2), c3 TIMESTAMP(2) ); INSERT INTO fractest VALUES ('17:51:04.777', '2018-09-08 17:51:04.777', '2018-09-08 17:51:04.777');
The temporal values are inserted into the table with rounding:
mysql> SELECT * FROM fractest; +-------------+------------------------+------------------------+ | c1 | c2 | c3 | +-------------+------------------------+------------------------+ | 17:51:04.78 | 2018-09-08 17:51:04.78 | 2018-09-08 17:51:04.78 | +-------------+------------------------+------------------------+
No warning or error is given when such rounding occurs. This behavior follows the SQL standard.
To insert the values with truncation instead, enable the
TIME_TRUNCATE_FRACTIONAL
SQL mode:SET @@sql_mode = sys.list_add(@@sql_mode, 'TIME_TRUNCATE_FRACTIONAL');
With that SQL mode enabled, the temporal values are inserted with truncation:
mysql> SELECT * FROM fractest; +-------------+------------------------+------------------------+ | c1 | c2 | c3 | +-------------+------------------------+------------------------+ | 17:51:04.77 | 2018-09-08 17:51:04.77 | 2018-09-08 17:51:04.77 | +-------------+------------------------+------------------------+
-
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 '
, andstr
'TIMESTAMP '
, 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 Literalsstr
'