Question

When I try to run the following query:

... WHERE `date` = DATE_ADD(NOW(), INTERVAL 10 HOUR)

It doesn’t work, so I have to use the $date = date("Y-m-d", strtotime('+10 hours'))

But why date_add doesn’t work?

Thanks much

Answer 1

Note that DATE_ADD() function returns a time part in addition to the date. This is not the same as using php’s date("Y-m-d", strtotime('+10 hours')), which only returns the date part.

SELECT DATE_ADD(NOW(), INTERVAL 10 HOUR);
+-----------------------------------+
| DATE_ADD(NOW(), INTERVAL 10 HOUR) |
+-----------------------------------+
| 2010-11-05 01:59:51               |
+-----------------------------------+
1 row in set (0.00 sec)

You could use WHERE date = DATE(DATE_ADD(NOW(), INTERVAL 10 HOUR)) instead:

SELECT DATE(DATE_ADD(NOW(), INTERVAL 10 HOUR));
+-----------------------------------------+
| DATE(DATE_ADD(NOW(), INTERVAL 10 HOUR)) |
+-----------------------------------------+
| 2010-11-05                              |
+-----------------------------------------+
1 row in set (0.02 sec)

Test case:

CREATE TABLE tbl (id int, date datetime);

INSERT INTO tbl VALUES (1, '2010-11-04');
INSERT INTO tbl VALUES (2, '2010-11-05');
INSERT INTO tbl VALUES (3, '2010-11-06');
INSERT INTO tbl VALUES (4, '2010-11-07');

SELECT * FROM tbl WHERE date = DATE(DATE_ADD(NOW(), INTERVAL 10 HOUR));
+------+---------------------+
| id   | date                |
+------+---------------------+
|    2 | 2010-11-05 00:00:00 |
+------+---------------------+
1 row in set (0.00 sec)