Testing String Equality or Relative Ordering

4.4.1 Problem

You want to know whether strings are equal or unequal, or which one appears first in lexical order.

4.4.2 Solution

Use a comparison operator.

4.4.3 Discussion

Strings are subject to the usual equality and inequality comparisons:

mysql> SELECT name, name = 'lead', name != 'lead' FROM metal;
+----------+---------------+----------------+
| name | name = 'lead' | name != 'lead' |
+----------+---------------+----------------+
| copper | 0 | 1 |
| gold | 0 | 1 |
| iron | 0 | 1 |
| lead | 1 | 0 |
| mercury | 0 | 1 |
| platinum | 0 | 1 |
| silver | 0 | 1 |
| tin | 0 | 1 |
+----------+---------------+----------------+

You can also use relational operators such as <, <=, >=, and > to test strings for lexical ordering:

mysql> SELECT name, name < 'lead', name > 'lead' FROM metal;
+----------+---------------+---------------+
| name | name < 'lead' | name > 'lead' |
+----------+---------------+---------------+
| copper | 1 | 0 |
| gold | 1 | 0 |
| iron | 1 | 0 |
| lead | 0 | 0 |
| mercury | 0 | 1 |
| platinum | 0 | 1 |
| silver | 0 | 1 |
| tin | 0 | 1 |
+----------+---------------+---------------+

To find out whether a string lies within a given range of values (inclusive), you can combine two comparisons:

mysql> SELECT name, 'iron' <= name AND name <= 'platinum' FROM metal;
+----------+---------------------------------------+
| name | 'iron' <= name AND name <= 'platinum' |
+----------+---------------------------------------+
| copper | 0 |
| gold | 0 |
| iron | 1 |
| lead | 1 |
| mercury | 1 |
| platinum | 1 |
| silver | 0 |
| tin | 0 |
+----------+---------------------------------------+

You can also use the BETWEEN operator for inclusive-range testing. The following query is equivalent to the one just shown:

SELECT name, name BETWEEN 'iron' AND 'platinum' FROM metal;

4.4.4 See Also

The outcome of a string comparison may be affected by whether or not the operands are binary strings, as discussed in Recipe 4.10.

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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