Treating Dates or Times as Numbers

5.29.1 Problem

You want to treat a temporal string as a number.

5.29.2 Solution

Perform a string-to-number conversion.

5.29.3 Discussion

In many cases, it is possible in MySQL to treat date and time values as numbers. This can sometimes be useful if you want to perform an arithmetic operation on the value. To force conversion of a temporal value to numeric form, add zero or use it in a numeric context:

mysql> SELECT t1,
 -> t1+0 AS 't1 as number',
 -> FLOOR(t1) AS 't1 as number',
 -> FLOOR(t1/10000) AS 'hour part'
 -> FROM time_val;
+----------+--------------+--------------+-----------+
| t1 | t1 as number | t1 as number | hour part |
+----------+--------------+--------------+-----------+
| 15:00:00 | 150000 | 150000 | 15 |
| 05:01:30 | 50130 | 50130 | 5 |
| 12:30:20 | 123020 | 123020 | 12 |
+----------+--------------+--------------+-----------+

The same kind of conversion can be performed for date or date-and-time values:

mysql> SELECT d, d+0 FROM date_val;
+------------+----------+
| d | d+0 |
+------------+----------+
| 1864-02-28 | 18640228 |
| 1900-01-15 | 19000115 |
| 1987-03-05 | 19870305 |
| 1999-12-31 | 19991231 |
| 2000-06-04 | 20000604 |
+------------+----------+
mysql> SELECT dt, dt+0 FROM datetime_val;
+---------------------+----------------+
| dt | dt+0 |
+---------------------+----------------+
| 1970-01-01 00:00:00 | 19700101000000 |
| 1987-03-05 12:30:15 | 19870305123015 |
| 1999-12-31 09:00:00 | 19991231090000 |
| 2000-06-04 15:45:30 | 20000604154530 |
+---------------------+----------------+

A value produced by adding zero is not the same as that produced by conversion into basic units like seconds or days. The result is essentially what you get by removing all the delimiters from the string representation of the original value. Also, conversion to numeric form works only for values that MySQL interprets temporally. If you try converting a literal string to a number by adding zero, you'll just get the first component:

mysql> SELECT '1999-01-01'+0, '1999-01-01 12:30:45'+0, '12:30:45'+0;
+----------------+-------------------------+--------------+
| '1999-01-01'+0 | '1999-01-01 12:30:45'+0 | '12:30:45'+0 |
+----------------+-------------------------+--------------+
| 1999 | 1999 | 12 |
+----------------+-------------------------+--------------+

This same thing happens with functions such as DATE_FORMAT( ) and TIME_FORMAT( ), or if you pull out parts of DATETIME or TIMESTAMP values with LEFT( ) or RIGHT( ). In +0 context, the results of these functions are treated as strings, not temporal types.