3.3.4.1 Selecting All Data

The simplest form of SELECT retrieves everything from a table:

mysql> SELECT * FROM pet;
+----------+--------+---------+------+------------+------------+
| name     | owner  | species | sex  | birth      | death      |
+----------+--------+---------+------+------------+------------+
| Fluffy   | Harold | cat     | f    | 1993-02-04 | NULL       |
| Claws    | Gwen   | cat     | m    | 1994-03-17 | NULL       |
| Buffy    | Harold | dog     | f    | 1989-05-13 | NULL       |
| Fang     | Benny  | dog     | m    | 1990-08-27 | NULL       |
| Bowser   | Diane  | dog     | m    | 1998-08-31 | 1995-07-29 |
| Chirpy   | Gwen   | bird    | f    | 1998-09-11 | NULL       |
| Whistler | Gwen   | bird    | NULL | 1997-12-09 | NULL       |
| Slim     | Benny  | snake   | m    | 1996-04-29 | NULL       |
| Puffball | Diane  | hamster | f    | 1999-03-30 | NULL       |
+----------+--------+---------+------+------------+------------+

This form of SELECT is useful if you want to review your entire table, for instance, after you've just loaded it with your initial dataset. As it happens, the output just shown reveals an error in your datafile: Bowser appears to have been born after he died! Consulting your original pedigree papers, you find that the correct birth year is 1989, not 1998.

There are least a couple of ways to fix this:

• Edit the file `pet.txt' to correct the error, then empty the table and reload it using DELETE and LOAD DATA:

  mysql> SET AUTOCOMMIT=1;  # Used for quick re-create of the table
  mysql> DELETE FROM pet;
  mysql> LOAD DATA LOCAL INFILE "pet.txt" INTO TABLE pet;
  

  However, if you do this, you must also re-enter the record for Puffball.
• Fix only the erroneous record with an UPDATE statement:

  mysql> UPDATE pet SET birth = "1989-08-31" WHERE name = "Bowser";
  

As shown above, it is easy to retrieve an entire table. But typically you don't want to do that, particularly when the table becomes large. Instead, you're usually more interested in answering a particular question, in which case you specify some constraints on the information you want. Let's look at some selection queries in terms of questions about your pets that they answer.

User Comments

DELETE FROM pet doesn't work if you are
using 'safe update mode' (which may be the case
during a tutorial).

Bowser's birthdate has already been corrected in the pets.txt file included in the tarball, which might confuse new guys like me ;-)

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