Calculating Dates by Substring Replacement
Problem
Given a date, you want to produce another date from it when you know that 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 | 1864-01-01 ...
Get MySQL Cookbook, 2nd Edition 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.