Retrieving information from database

The only purpose in storing information is to have it available when you need it. A database lives to answer questions. What pets are for sale? Who are the members? How many members live in Arkansas? Do you have an alligator for sale? How much does a dragon cost? What is Goliath Smith’s phone number? And on and on. You use the SELECT query to ask the database questions.
The simplest, basic SELECT query is

SELECT * FROM tablename

This query retrieves all the information from the table. The asterisk (*) is a wildcard meaning all the columns.
The SELECT query can be much more selective. SQL words and phrases in the SELECT query can pinpoint the information needed to answer your question. You can specify what information you want, how you want it organized, and the source of the information:

• You can request only the information (the columns) that you need to answer your question. For instance, you can request only the first and last names to create a list of members.
• You can request information in a particular order. For instance, you can request that the information be sorted in alphabetical order.
• You can request information from selected objects (the rows) in your table. For instance, you can request the first and last names for only those members whose addresses are in Florida.

In MySQL 4.1, MySQL added the ability to nest a SELECT query inside another query. The nested query is called a subquery. You can use a subquery in SELECT, INSERT, UPDATE, or DELETE queries or in SET clauses. A subquery can return a single value, a single row or column, or a table, which is used in the outer query. All the features of SELECT queries can be used in subqueries. See the MySQL online manual at dev.mysql.com/doc/refman/5.0/en/ subqueries.html for detailed information on using subqueries.