Changing the return type of the following functions:
- CURRENT_TIMESTAMP, CURRENT_TIMESTAMP(), NOW()
- SYSDATE()
- FROM_UNIXTIME()
from DATETIME to TIMESTAMP.
Note, the old function NOW() returning DATETIME is still available
as LOCALTIMESTAMP or LOCALTIMESTAMP(), e.g.:
SELECT
LOCALTIMESTAMP, -- DATETIME
CURRENT_TIMESTAMP; -- TIMESTAMP
The change in the functions return data type fixes some problems
that occurred near a DST change:
- Problem #1
INSERT INTO t1 (timestamp_field) VALUES (CURRENT_TIMESTAMP);
INSERT INTO t1 (timestamp_field) VALUES (COALESCE(CURRENT_TIMESTAMP));
could result into two different values inserted.
- Problem #2
INSERT INTO t1 (timestamp_field) VALUES (FROM_UNIXTIME(1288477526));
INSERT INTO t1 (timestamp_field) VALUES (FROM_UNIXTIME(1288477526+3600));
could result into two equal TIMESTAMP values near a DST change.
Additional changes:
- FROM_UNIXTIME(0) now returns SQL NULL instead of '1970-01-01 00:00:00'
(assuming time_zone='+00:00')
- UNIX_TIMESTAMP('1970-01-01 00:00:00') now returns SQL NULL instead of 0
(assuming time_zone='+00:00'
These additional changes are needed for consistency with TIMESTAMP fields,
which cannot store '1970-01-01 00:00:00 +00:00'
