Database Reference
In-Depth Information
Chapter 7. Selecting Data
Previous chapters discussed the important topics of organizing your tables well and getting
data in to them. In this chapter, we will cover a key objective that makes the others pay off:
retrieving the data stored in a database. This is commonlycalled a
database query
.
The simplest way to retrieve data from a MySQL or MariaDB database —
to select
data —
is to use the SQL statement,
SELECT
. We used this SQL statement a few times in previous
chapters. In this chapter, we will cover it in greater detail. It's not necessary to know or use
all of the may options, but some techniques such as joining tables together are basic to us-
ing relational databases.
We'll begin this chapter by reviewing the basics of the
SELECT
statement, and then pro-
gress to more involved variants. When you finish this chapter, you will hopefully have a
good understanding of how to use
SELECT
for most of your needs as you start out as a
database developer, as well as be prepared for the many possibilities and special situations
that may arise over the years of developing databases with MySQL and MariaDB.
In previous chapters, especially in the exercises, you were asked to enter data into the
tables that we created and altered in the chapters of the previous part of this topic. Entering
data on your own was good for training purposes, but we now need much more data in our
database to better appreciate the examples in this chapter. If you haven't done so already,
go to
this topic's website
and download the dump files that contain tables of data.
Download
rookery.sql
to get the whole
rookery
database, with plenty of data for use in
our explorations. Once you have the dump file on your system (let's assume you put it in
/tmp/rookery.sql
), enter the following from the command line:
mysql --user='
your_name
' -p \
rookery < /tmp/rookery.sql
The command prompts for your password, logs you in using the username assigned to you,
and runs the statements in the
rookery.sql
file on the
rookery
database. If everything
goes well, there should be no message in response, just the command-line prompt when it's
finished.
