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3.6 Examples of Common Queries
==============================
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* example-maximum-column The Maximum Value for a Column
* example-maximum-row The Row Holding the Maximum of a Certain Column
* example-maximum-column-group Maximum of Column per Group
* example-maximum-column-group-row The Rows Holding the Group-wise Maximum of a Certain Field
* example-user-variables Using User-Defined Variables
* example-foreign-keys Using Foreign Keys
* searching-on-two-keys Searching on Two Keys
* calculating-days Calculating Visits Per Day
* example-auto-increment Using `AUTO_INCREMENT'
Here are examples of how to solve some common problems with MySQL.
Some of the examples use the table `shop' to hold the price of each
article (item number) for certain traders (dealers). Supposing that
each trader has a single fixed price per article, then (`article',
`dealer') is a primary key for the records.
Start the command-line tool `mysql' and select a database:
shell> mysql YOUR-DATABASE-NAME
(In most MySQL installations, you can use the database named `test').
You can create and populate the example table with these statements:
mysql> CREATE TABLE shop (
-> article INT(4) UNSIGNED ZEROFILL DEFAULT '0000' NOT NULL,
-> dealer CHAR(20) DEFAULT '' NOT NULL,
-> price DOUBLE(16,2) DEFAULT '0.00' NOT NULL,
-> PRIMARY KEY(article, dealer));
mysql> INSERT INTO shop VALUES
-> (1,'A',3.45),(1,'B',3.99),(2,'A',10.99),(3,'B',1.45),
-> (3,'C',1.69),(3,'D',1.25),(4,'D',19.95);
After issuing the statements, the table should have the following
contents:
mysql> SELECT * FROM shop;
+---------+--------+-------+
| article | dealer | price |
+---------+--------+-------+
| 0001 | A | 3.45 |
| 0001 | B | 3.99 |
| 0002 | A | 10.99 |
| 0003 | B | 1.45 |
| 0003 | C | 1.69 |
| 0003 | D | 1.25 |
| 0004 | D | 19.95 |
+---------+--------+-------+
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