Calculating One Date from Another by Substring Replacement
Problem
Given a date, you want to produce another date from it, and you know the two dates share some components in common.
Solution
Treat a date or time value as a string and perform direct replacement on parts of the string.
Discussion
In some cases, you can use substring replacement to calculate dates
without performing any date arithmetic. For example, you can use
string operations to produce the first-of-month value for a given
date by replacing the day component with 01
. You
can do this either with DATE_FORMAT( )
or with CONCAT( )
:
mysql>SELECT d,
->DATE_FORMAT(d,'%Y-%m-01') AS method1,
->CONCAT(YEAR(d),'-',LPAD(MONTH(d),2,'0'),'-01') AS method2
->FROM date_val;
+------------+------------+------------+ | d | method1 | method2 | +------------+------------+------------+ | 1864-02-28 | 1864-02-01 | 1864-02-01 | | 1900-01-15 | 1900-01-01 | 1900-01-01 | | 1987-03-05 | 1987-03-01 | 1987-03-01 | | 1999-12-31 | 1999-12-01 | 1999-12-01 | | 2000-06-04 | 2000-06-01 | 2000-06-01 | +------------+------------+------------+
The string replacement technique can also be used to produce dates
with a specific position within the calendar year. For New
Year’s Day (January 1), replace the month and day
with 01
:
mysql>SELECT d,
->DATE_FORMAT(d,'%Y-01-01') AS method1,
->CONCAT(YEAR(d),'-01-01') AS method2
->FROM date_val;
+------------+------------+------------+ | d | method1 | method2 | +------------+------------+------------+ | 1864-02-28 ...
Get MySQL Cookbook now with the O’Reilly learning platform.
O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.