Microseconds in MariaDB

In MariaDB 5.3, the TIME, DATETIME, and TIMESTAMP types, along with the temporal functions, CAST and dynamic columns, now support microseconds. The datetime precision of a column can be specified when creating the table with CREATE TABLE, for example:

CREATE TABLE example(
  col_microsec DATETIME(6),
  col_millisec TIME(3)
);

Generally, the precision can be specified for any TIME, DATETIME, or TIMESTAMP column, in parentheses, after the type name. The datetime precision specifies number of digits after the decimal dot and can be any integer number from 0 to 6. If no precision is specified it is assumed to be 0, for backward compatibility reasons.

As one can expect, a datetime precision can be specified wherever a type name is used. For example:

• when declaring arguments of stored routines.
• when specifying a return type of a stored function.
• when declaring variables.
• in a CAST function:

  create function example(x datetime(5)) returns time(4)
  begin
    declare y timestamp(6);
    return cast(x as time(2));
  end;

Additional Information:

Some additional notes, in no specific order:

• when comparing anything to a temporal value (DATETIME, TIME, DATE, or TIMESTAMP), both values are compared as temporal values, not as strings.
• INFORMATION_SCHEMA.COLUMNS has a new column DATETIME_PRECISION
• NOW(), CURTIME(), UTC_TIMESTAMP(), UTC_TIME(), CURRENT_TIME(), CURRENT_TIMESTAMP(), LOCALTIME(), and LOCALTIMESTAMP() now accept datetime precision as an optional argument. For example:

  SELECT CURTIME(4);
  --> 10:11:12.3456

• TIME_TO_SEC() and UNIX_TIMESTAMP() preserve microseconds of the argument. These functions will return a decimal number if the result non-zero datetime precision and an integer otherwise (for backward compatibility).

  SELECT TIME_TO_SEC('10:10:10.12345');
  --> 36610.12345

• Current versions of this patch fix a bug in the following optimization: in certain queries with DISTINCT MariaDB can ignore this clause if it can prove that all result rows are unique anyway, for example, when a primary key is compared with a constant. Sometimes this optimization was applied incorrectly, though — for example, when comparing a string with a date constant. This is now fixed.
• DATE_ADD() and DATE_SUB() functions can now take a TIME expression as an argument (not just DATETIME as before).

  SELECT TIME('10:10:10') + INTERVAL 100 MICROSECOND;
  --> 10:10:10.000100

• The event_time field in the mysql.general_log table and the start_time, query_time, and lock_time fields in the mysql.slow_log table now store values with microsecond precision.
• This patch fixed a bug when comparing a temporal value using the BETWEEN operator and one of the operands is NULL.
• The old syntax TIMESTAMP(N), where N is the display width, is no longer supported. It was deprecated in MySQL 4.1.0 (released on 2003-04-03).
• when a DATETIME value is compared to a TIME value, the latter is treated as a full datetime with a zero date part, similar to comparing DATE to a DATETIME, or to comparing DECIMAL numbers. Earlier versions of MariaDB used to compare only the time part of both operands in such a case.

SELECT CAST('2009-12-31 23:59:59.998877' as DATETIME(3));
-> 2009-12-31 23:59:59.998