October 2002
Intermediate to advanced
1024 pages
27h 26m
English
Given a date, you want to produce another date from it, and you know the two dates share some components in common.
Treat a date or time value as a string and perform direct replacement on parts of the string.
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 ...