SQL - グループ化と集約化(group by 節)

初めてのSQL
Alan Beaulieu (著)

開発環境

• OS: OS X Lion - Apple
• データベース言語: SQL
• リレーショナルデータベース: MySQL

『初めてのSQL』(Alan Beaulieu 著、株式会社クイープ 翻訳、オライリー・ジャパン、2006年、ISBN4-8733-181-8) の8章(グループ化と集約化)、8.5(練習問題)8-2を解いてみる。

8-2.

SQL文(BBEdit)

SELECT account_id,  COUNT(*)
FROM account
GROUP BY cust_id;

入出力結果(Terminal)

$ mysql -u lrngsql -p bank
Enter password: 
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 4
Server version: 5.5.24 MySQL Community Server (GPL)

Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> desc account;
+--------------------+----------------------------------+------+-----+---------+----------------+
| Field              | Type                             | Null | Key | Default | Extra          |
+--------------------+----------------------------------+------+-----+---------+----------------+
| account_id         | int(10) unsigned                 | NO   | PRI | NULL    | auto_increment |
| product_cd         | varchar(10)                      | NO   | MUL | NULL    |                |
| cust_id            | int(10) unsigned                 | NO   | MUL | NULL    |                |
| open_date          | date                             | NO   |     | NULL    |                |
| close_date         | date                             | YES  |     | NULL    |                |
| last_activity_date | date                             | YES  |     | NULL    |                |
| status             | enum('ACTIVE','CLOSED','FROZEN') | YES  |     | NULL    |                |
| open_branch_id     | smallint(5) unsigned             | YES  | MUL | NULL    |                |
| open_emp_id        | smallint(5) unsigned             | YES  | MUL | NULL    |                |
| avail_balance      | float(10,2)                      | YES  |     | NULL    |                |
| pending_balance    | float(10,2)                      | YES  |     | NULL    |                |
+--------------------+----------------------------------+------+-----+---------+----------------+
11 rows in set (0.10 sec)

mysql> SELECT account_id,  COUNT(*)
    -> FROM account
    -> GROUP BY cust_id;
+------------+----------+
| account_id | COUNT(*) |
+------------+----------+
|          1 |        3 |
|          4 |        2 |
|          7 |        2 |
|         10 |        3 |
|         13 |        1 |
|         14 |        2 |
|         17 |        1 |
|         18 |        2 |
|         21 |        3 |
|         24 |        2 |
|         27 |        1 |
|         28 |        1 |
|         29 |        1 |
+------------+----------+
13 rows in set (0.08 sec)

mysql> quit
Bye
$