5.9. Synthesizing Dates or Times Using Component-Extraction Functions

5.9.1. Problem

You have the parts of a date or time and want to combine them to produce a date or time value.

5.9.2. Solution

Put the parts together using CONCAT( ).

5.9.3. Discussion

Another way to construct temporal values is to use date-part extraction functions in conjunction with CONCAT( ). However, this method often is messier than the DATE_FORMAT( ) technique discussed in Recipe 5.8—and it sometimes yields slightly different results:

mysql> SELECT d,
    -> CONCAT(YEAR(d),'-',MONTH(d),'-01')
    -> FROM date_val;
+------------+------------------------------------+
| d          | CONCAT(YEAR(d),'-',MONTH(d),'-01') |
+------------+------------------------------------+
| 1864-02-28 | 1864-2-01                          |
| 1900-01-15 | 1900-1-01                          |
| 1987-03-05 | 1987-3-01                          |
| 1999-12-31 | 1999-12-01                         |
| 2000-06-04 | 2000-6-01                          |
+------------+------------------------------------+

Note that the month values in some of these dates have only a single digit. To ensure that the month has two digits—as required for ISO format—use LPAD( ) to add a leading zero as necessary:

mysql> SELECT d,
    -> CONCAT(YEAR(d),'-',LPAD(MONTH(d),2,'0'),'-01')
    -> FROM date_val;
+------------+------------------------------------------------+
| d          | CONCAT(YEAR(d),'-',LPAD(MONTH(d),2,'0'),'-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                                     |
+------------+------------------------------------------------+

Another way to solve this problem is given in Recipe 5.19.

TIME values can be produced from hours, minutes, and seconds values using methods analogous to those for creating DATE values. For example, to change a TIME value so that its seconds part is 00, extract the hour and minute parts, then recombine them using TIME_FORMAT( ) or CONCAT( ):

mysql> SELECT t1,
    -> TIME_FORMAT(t1,'%H:%i:00') AS method1,
    -> CONCAT(LPAD(HOUR(t1),2,'0'),':',LPAD(MINUTE(t1),2,'0'),':00') AS method2
    -> FROM time_val;
+----------+----------+----------+
| t1       | method1  | method2  |
+----------+----------+----------+
| 15:00:00 | 15:00:00 | 15:00:00 |
| 05:01:30 | 05:01:00 | 05:01:00 |
| 12:30:20 | 12:30:00 | 12:30:00 |
+----------+----------+----------+