A Complete Guide To MySQL DATETIME Data Type
Summary: in this tutorial, you will learn about MySQL DATETIME
data type and how to use some handy functions for manipulating DATETIME
effectively.
Introduction to MySQL DATETIME data type
You use MySQL DATETIME
to store a value that contains both date and time. When you query data from a DATETIME
column, MySQL displays the DATETIME
value in the following format:
YYYY-MM-DD HH:MM:SS
By default, DATETIME
values range from 1000-01-01 00:00:00
to 9999-12-31 23:59:59
.
A DATETIME
the value uses 5 bytes for storage. In addition, a DATETIME
value can include a trailing fractional second up to microseconds with the format YYYY-MM-DD HH:MM:SS[.fraction]
e.g., 2015-12-20 10:01:00.999999
. When including the fractional second precision, DATETIME
values require more storage as illustrated in the following table:
Fractional Seconds Precision | Storage (Bytes) |
---|---|
0 | 0 |
1, 2 | 1 |
3, 4 | 2 |
5, 6 | 3 |
For example, 2015-12-20 10:01:00.999999
requires 8 bytes, 5 bytes for 2015-12-20 10:01:00
and 3 bytes for .999999
while 2015-12-20 10:01:00.9
requires only 6 bytes, 1 byte for the fractional second precision.
Note that before MySQL 5.6.4, DATETIME
values require 8 bytes storage instead of 5 bytes.
MySQL DATETIME vs. TIMESTAMP
MySQL provides another temporal data type that is similar to the DATETIME
called TIMESTAMP
.
The TIMESTAMP
requires 4 bytes while DATETIME
requires 5 bytes. Both TIMESTAMP
and DATETIME
require additional bytes for fractional seconds precision.
TIMESTAMP
values range from 1970-01-01 00:00:01 UTC
2038-01-19 03:14:07 UTC
. If you want to store temporal values that are beyond 2038, you should use DATETIME
instead of TIMESTAMP
.
MySQL stores TIMESTAMP
in UTC value. However, MySQL stores the DATETIME
value as is without a timezone. Let’s see the following example.
First, set the timezone of the current connection to +00:00
.
SET time_zone = '+00:00';
Next, create a table named timestamp_n_datetime
that consists of two columns: ts
and dt
with TIMESTAMP
and DATETIME
types using the following statement.
CREATE TABLE timestamp_n_datetime (
id INT AUTO_INCREMENT PRIMARY KEY,
ts TIMESTAMP,
dt DATETIME
);
Then, insert the current date and time into both ts
and dt
columns of the timestamp_n_datetime
table,
INSERT INTO timestamp_n_datetime(ts,dt)
VALUES(NOW(),NOW());
After that, query data from the timestamp_n_datetime
table.
SELECT
ts,
dt
FROM
timestamp_n_datetime;
Both values in DATETIME
and TIMESTAMP
columns are the same.
Finally, set the connection’s time zone to +03:00
and query data from the timestamp_n_datetime
table again.
SET time_zone = '+03:00';
SELECT
ts,
dt
FROM
timestamp_n_datetime;
As you can see, the value in the TIMESTAMP
column is different. This is because the TIMESTAMP
column stores the date and time value in UTC when we changed the time zone, the value of the TIMESTAMP
column is adjusted according to the new time zone.
It means that if you use the TIMESTAMP
data to store date and time values, you should take serious consideration when you move your database to a server located in a different time zone.
MySQL DATETIME functions
The following statement sets the variable @dt
to the current date and time using the NOW()
function.
SET @dt = NOW();
To query the value of the @dt
variable, you use the following SELECT
statement:
SELECT @dt;
MySQL DATE function
To extract the date portion from a DATETIME
value, you use the DATE
function as follows:
SELECT DATE(@dt);
Let’s see the following example.
CREATE TABLE test_dt (
id INT AUTO_INCREMENT PRIMARY KEY,
created_at DATETIME
);
INSERT INTO test_dt(created_at)
VALUES('2015-11-05 14:29:36');
Suppose you want to know which row created on 2015-11-05
, you use the following query:
SELECT
*
FROM
test_dt
WHERE
created_at = '2015-11-05';
It returns no rows.
This is because the created_at
column contains not only date but also time. To correct it, you use the DATE
function as follows:
SELECT
*
FROM
test_dt
WHERE
DATE(created_at) = '2015-11-05';
It returns one row as expected. In case the table has many rows, MySQL has to perform a full table scan to locate the rows that match the condition.
MySQL TIME function
To extract the time portion from a DATETIME
value, you use the TIME
function as the following statement:
SELECT TIME(@dt);
MySQL YEAR, QUARTER, MONTH, WEEK, DAY, HOUR, MINUTE, and SECOND functions
To get the year, quarter, month, week, day, hour, minute, and second from a DATETIME
value, you use the functions as shown in the following statement:
SELECT
HOUR(@dt),
MINUTE(@dt),
SECOND(@dt),
DAY(@dt),
WEEK(@dt),
MONTH(@dt),
QUARTER(@dt),
YEAR(@dt);
MySQL DATE_FORMAT function
To format a DATETIME
value, you use the DATE_FORMAT
function. For example, the following statement formats a DATETIME
value based on the %H:%i:%s - %W %M %Y
format:
SELECT DATE_FORMAT(@dt, '%H:%i:%s - %W %M %Y');
MySQL DATE_ADD function
To add an interval to a DATETIME
value, you use DATE_ADD
function as follows:
SELECT @dt start,
DATE_ADD(@dt, INTERVAL 1 SECOND) '1 second later',
DATE_ADD(@dt, INTERVAL 1 MINUTE) '1 minute later',
DATE_ADD(@dt, INTERVAL 1 HOUR) '1 hour later',
DATE_ADD(@dt, INTERVAL 1 DAY) '1 day later',
DATE_ADD(@dt, INTERVAL 1 WEEK) '1 week later',
DATE_ADD(@dt, INTERVAL 1 MONTH) '1 month later',
DATE_ADD(@dt, INTERVAL 1 YEAR) '1 year later';
MySQL DATE_SUB function
To subtract an interval from a DATETIME
value, you use DATE_SUB
function as follows:
SELECT @dt start,
DATE_SUB(@dt, INTERVAL 1 SECOND) '1 second before',
DATE_SUB(@dt, INTERVAL 1 MINUTE) '1 minute before',
DATE_SUB(@dt, INTERVAL 1 HOUR) '1 hour before',
DATE_SUB(@dt, INTERVAL 1 DAY) '1 day before',
DATE_SUB(@dt, INTERVAL 1 WEEK) '1 week before',
DATE_SUB(@dt, INTERVAL 1 MONTH) '1 month before',
DATE_SUB(@dt, INTERVAL 1 YEAR) '1 year before';
MySQL DATE_DIFF function
To calculate a difference in days between two DATETIME
values, you use the DATEDIFF
function. Notice that the DATEDIFF
function only considers the date part of a DATETIME
value in the calculation.
See the following example.
First, create a table named datediff_test
that has one column whose data type is DATETIME
.
CREATE TABLE datediff_test (
dt DATETIME
);
Second, insert some rows into the datediff_test
table.
INSERT INTO datediff_test(dt)
VALUES('2010-04-30 07:27:39'),
('2010-05-17 22:52:21'),
('2010-05-18 01:19:10'),
('2010-05-22 14:17:16'),
('2010-05-26 03:26:56'),
('2010-06-10 04:44:38'),
('2010-06-13 13:55:53');
Third, use the DATEDIFF
function to compare the current date and time with the value in each row of the datediff_test
table.
SELECT
dt,
DATEDIFF(NOW(), dt)
FROM
datediff_test;
In this tutorial, you have learned about MySQL DATETIME
datatype and some useful DATETIME
functions.
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