# 3.6. Examples of Common Queries

3.6.1. The Maximum Value for a Column
3.6.2. The Row Holding the Maximum of a Certain Column
3.6.3. Maximum of Column per Group
3.6.4. The Rows Holding the Group-wise Maximum of a Certain Column
3.6.5. Using User-Defined Variables
3.6.6. Using Foreign Keys
3.6.7. Searching on Two Keys
3.6.8. Calculating Visits Per Day
3.6.9. 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:

`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));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:

`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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