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 5.8and 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 digitsas required for ISO formatuse 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 |
+----------+----------+----------+

Using the mysql Client Program

Writing MySQL-Based Programs

Record Selection Techniques

Working with Strings

Working with Dates and Times

Sorting Query Results

Generating Summaries

Modifying Tables with ALTER TABLE

Obtaining and Using Metadata

Importing and Exporting Data

Generating and Using Sequences

Using Multiple Tables

Statistical Techniques

Handling Duplicates

Performing Transactions

Introduction to MySQL on the Web

Incorporating Query Resultsinto Web Pages

Processing Web Input with MySQL

Using MySQL-Based Web Session Management

Appendix A. Obtaining MySQL Software

Appendix B. JSP and Tomcat Primer

Appendix C. References



MySQL Cookbook
MySQL Cookbook
ISBN: 059652708X
EAN: 2147483647
Year: 2005
Pages: 412
Authors: Paul DuBois

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