SpirirHost Support Centre: MySQL Reference Manual p.171

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Table of Contents
1. General Information
2. MySQL Installation
3. Tutorial Introduction
4. Database Administration
5. MySQL Optimisation
6. MySQL Language Reference
7. MySQL Table Types
8. MySQL APIs
9. Extending MySQL

Chapter 3: Tutorial Introduction 171 3.5.5 Using user variables You can use MySQL user variables to remember results without having to store them in temporary variables in the client. See Section 6.1.4 [Variables], page 381. For example, to nd the articles with the highest and lowest price you can do: mysql> SELECT @min_price:=MIN(price),@max_price:=MAX(price) FROM shop; mysql> SELECT * FROM shop WHERE price=@min_price OR price=@max_price; +---------+--------+-------+ | article | dealer | price | +---------+--------+-------+ | 0003 | D | 1.25 | | 0004 | D | 19.95 | +---------+--------+-------+ 3.5.6 Using Foreign Keys In MySQL 3.23.44 and up, InnoDB tables supports checking of foreign key constraints. See Section 7.5 [InnoDB], page 506. See also Section 1.7.4.5 [ANSI di Foreign Keys], page 38. You don't actually need foreign keys to join 2 tables. The only thing MySQL currently doesn't do (in type types other than InnoDB), is CHECK to make sure that the keys you use really exist in the table(s) you're referencing and it doesn't automatically delete rows from a table with a foreign key denition. If you use your keys like normal, it'll work just ne: CREATE TABLE person ( id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT, name CHAR(60) NOT NULL, PRIMARY KEY (id) ); CREATE TABLE shirt ( id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT, style ENUM('t-shirt', 'polo', 'dress') NOT NULL, color ENUM('red', 'blue', 'orange', 'white', 'black') NOT NULL, owner SMALLINT UNSIGNED NOT NULL REFERENCES person(id), PRIMARY KEY (id) ); INSERT INTO person VALUES (NULL, 'Antonio Paz'); INSERT INTO shirt VALUES (NULL, 'polo', 'blue', LAST_INSERT_ID()), (NULL, 'dress', 'white', LAST_INSERT_ID()), (NULL, 't-shirt', 'blue', LAST_INSERT_ID()); INSERT INTO person VALUES (NULL, 'Lilliana Angelovska');

MySQL Reference Manual

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