Synthesizing Dates or Times Using Formatting Functions

5.8.1 Problem

You want to produce a new date from a given date by replacing parts of its values.

5.8.2 Solution

Use DATE_FORMAT( ) or TIME_FORMAT( ) to combine parts of the existing value with parts you want to replace.

5.8.3 Discussion

The complement of splitting apart a date or time value is synthesizing one from its constituent parts. Techniques for date and time synthesis include using formatting functions (discussed here) and string concatenation (discussed in Recipe 5.9).

Date synthesis often is performed by beginning with a given date, then keeping parts that you want to use and replacing the rest. For example, to find the first day of the month in which a date falls, use DATE_FORMAT( ) to extract the year and month parts from the date and combine them with a day value of 01:

mysql> SELECT d, DATE_FORMAT(d,'%Y-%m-01') FROM date_val;
+------------+---------------------------+
| d | DATE_FORMAT(d,'%Y-%m-01') |
+------------+---------------------------+
| 1864-02-28 | 1864-02-01 |
| 1900-01-15 | 1900-01-01 |
| 1987-03-05 | 1987-03-01 |
| 1999-12-31 | 1999-12-01 |
| 2000-06-04 | 2000-06-01 |
+------------+---------------------------+

TIME_FORMAT( ) can be used in a similar way:

mysql> SELECT t1, TIME_FORMAT(t1,'%H:%i:00') FROM time_val;
+----------+----------------------------+
| t1 | TIME_FORMAT(t1,'%H:%i:00') |
+----------+----------------------------+
| 15:00:00 | 15:00:00 |
| 05:01:30 | 05:01:00 |
| 12:30:20 | 12:30:00 |
+----------+----------------------------+