Home arrow MySQL arrow Page 2 - Speaking SQL (part 2)

Christmas Presents - MySQL

After learning how to insert and edit data in a database, thesecond part of our SQL tutorial takes an in-depth look at the SELECTquery,and explains how to use joins, sub-queries and built-in functions tofocus in on the data you need.

TABLE OF CONTENTS:
  1. Speaking SQL (part 2)
  2. Christmas Presents
  3. Teacher's Pet
  4. Reading Backwards
  5. Count() Me In
  6. Like, You Know, Man...
  7. Joining Them Together
  8. Nest Egg
By: icarus, (c) Melonfire
Rating: starstarstarstarstar / 5
January 18, 2001

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Throughout this article, I'll be using the database I developed last time to better illustrate the various examples. Just to refresh your memory, here's what it looked like:

# members table +-----------+-------+---------+---------+--------------------------+ | member_id | fname | lname | tel | email | +-----------+-------+---------+---------+--------------------------+ | 1 | John | Doe | 1234567 | jdoe@somewhere.com | | 2 | Jane | Doe | 8373728 | jane@site.com | | 3 | Steve | Klingon | 7449373 | steve@alien-race.com | | 4 | Santa | Claus | 9999999 | santa@the-north-pole.com | +-----------+-------+---------+---------+--------------------------+ # videos table +----------+-------------------------------+------------------+ | video_id | title | director | +----------+-------------------------------+------------------+ | 1 | Star Wars: The Phantom Menace | George Lucas | | 2 | ET | Steven Spielberg | | 3 | Charlie's Angels | McG | | 4 | Any Given Sunday | Oliver Stone | | 5 | Hollow Man | Paul Verhoeven | | 6 | Woman On Top | Fina Torres | +----------+-------------------------------+------------------+ # status table +-----------+----------+ | member_id | video_id | +-----------+----------+ | 2 | 6 | | 4 | 2 | | 1 | 1 | | 1 | 2 | | 1 | 3 | +-----------+----------+
The simplest form of the SELECT query is the "catch-all" query, which returns all the records in a specific table. It looks like this:

mysql> SELECT * FROM members; +-----------+-------+---------+---------+----------------------------+ | member_id | fname | lname | tel | email | +-----------+-------+---------+---------+----------------------------+ | 1 | John | Doe | 1234567 | jdoe@somewhere.com | | 2 | Jane | Doe | 8373728 | jane@site.com | | 3 | Steve | Klingon | 7449373 | steve@alien-race.com | | 4 | Santa | Claus | 9999999 | santa@the-north-pole.com | +-----------+-------+---------+---------+----------------------------+ 4 rows in set (0.00 sec)
The asterisk (*) indicates that you'd like to see all the columns present in the table. If, instead, you'd prefer to see one or two specific columns only in the result set, you can specify the column name(s) in the SELECT statement, like this:

mysql> SELECT lname FROM members; +---------+ | lname | +---------+ | Doe | | Doe | | Klingon | | Claus | +---------+ 4 rows in set (0.00 sec)
You can eliminate duplicate entries using the DISTINCT keyword - the following query will not display members with the last name "Doe" more than once.

mysql> SELECT DISTINCT lname FROM members; +---------+ | lname | +---------+ | Doe | | Klingon | | Claus | +---------+ 3 rows in set (0.05 sec)


This article copyright Melonfire 2001. All rights reserved. {mospagebreak title=Where, Oh Where, Art Thou?} Of course, the whole idea of structuring data into rows and columns is to make it easier to get a focused result set. And a great part of that focus comes from the WHERE clause (maybe you remember this from the UPDATE and DELETE statements you learnt last time) to the SELECT statement, which allows you to define specific criteria for the result set. Records that do not meet the specified criteria will not appear in the result set.

For example, let's suppose that you wanted to see a list of all members with the last name "Doe".

mysql> SELECT * FROM members WHERE lname = "Doe"; +-----------+-------+-------+---------+--------------------+ | member_id | fname | lname | tel | email | +-----------+-------+-------+---------+--------------------+ | 1 | John | Doe | 1234567 | jdoe@somewhere.com | | 2 | Jane | Doe | 8373728 | jane@site.com | +-----------+-------+-------+---------+--------------------+ 2 rows in set (0.00 sec)
Or let's suppose that you wanted Santa Claus' email address:

mysql> SELECT email FROM members WHERE fname = "Santa"; +----------------------------+ | email | +----------------------------+ | santa@the-north-pole.com | +----------------------------+ 1 row in set (0.06 sec)
Or even that you wanted to see a list of all movies by George Lucas.

mysql> SELECT title, director FROM videos WHERE director = "George Lucas"; +-------------------------------+--------------+ | title | director | +-------------------------------+--------------+ | Star Wars: The Phantom Menace | George Lucas | +-------------------------------+--------------+ 1 row in set (0.06 sec)
Yes, I know the collection is incomplete. Maybe I should write to Santa for the other three.

This article copyright Melonfire 2001. All rights reserved.

 
 
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