MySQL Tutorial/Aggregate Functions/Introduction — различия между версиями
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Текущая версия на 09:49, 26 мая 2010
Aggregate Functions
Aggregate functions perform a mathematical operation on a column.
MySQL implements the following aggregate functions:
- COUNT(),
- COUNT(DISTINCT),
- MAX(),
- MIN(),
- AVG(),
- SUM(), and
- STD().
16. 1. Introduction 16. 1. 1. Aggregate Functions 16. 1. 2. <A href="/Tutorial/MySQL/0320__Aggregate-Functions/Usetwoaggregatefunctionsinaselectstatement.htm">Use two aggregate functions in a select statement</a> 16. 1. 3. <A href="/Tutorial/MySQL/0320__Aggregate-Functions/Useaggregatefunctionwithgroupbyclause.htm">Use aggregate function with group by clause</a>
Use aggregate function with group by clause
mysql>
mysql>
mysql> CREATE TABLE Topic(
-> TopicID SMALLINT NOT NULL AUTO_INCREMENT PRIMARY KEY,
-> Name VARCHAR(50) NOT NULL,
-> InStock SMALLINT UNSIGNED NOT NULL,
-> OnOrder SMALLINT UNSIGNED NOT NULL,
-> Reserved SMALLINT UNSIGNED NOT NULL,
-> Department ENUM("Classical", "Popular") NOT NULL,
-> Category VARCHAR(20) NOT NULL,
-> RowUpdate TIMESTAMP NOT NULL
-> );
Query OK, 0 rows affected (0.02 sec)
mysql>
mysql>
mysql> INSERT INTO Topic (Name, InStock, OnOrder, Reserved, Department, Category) VALUES
-> ("Java", 10, 5, 3, "Popular", "Rock"),
-> ("JavaScript", 10, 5, 3, "Classical", "Opera"),
-> ("C Sharp", 17, 4, 1, "Popular", "Jazz"),
-> ("C", 9, 4, 2, "Classical", "Dance"),
-> ("C++", 24, 2, 5, "Classical", "General"),
-> ("Perl", 16, 6, 8, "Classical", "Vocal"),
-> ("Python", 2, 25, 6, "Popular", "Blues"),
-> ("Php", 32, 3, 10, "Popular", "Jazz"),
-> ("ASP.net", 12, 15, 13, "Popular", "Country"),
-> ("VB.net", 5, 20, 10, "Popular", "New Age"),
-> ("VC.net", 24, 11, 14, "Popular", "New Age"),
-> ("UML", 42, 17, 17, "Classical", "General"),
-> ("www.sqle.ru",25, 44, 28, "Classical", "Dance"),
-> ("Oracle", 32, 15, 12, "Classical", "General"),
-> ("Pl/SQL", 20, 10, 5, "Classical", "Opera"),
-> ("Sql Server", 23, 12, 8, "Classical", "General");
Query OK, 16 rows affected (0.02 sec)
Records: 16 Duplicates: 0 Warnings: 0
mysql>
mysql> select * from Topic;
+---------+----------------+---------+---------+----------+------------+----------+---------------------+
| TopicID | Name | InStock | OnOrder | Reserved | Department | Category | RowUpdate |
+---------+----------------+---------+---------+----------+------------+----------+---------------------+
| 1 | Java | 10 | 5 | 3 | Popular | Rock | 2007-07-23 19:09:42 |
| 2 | JavaScript | 10 | 5 | 3 | Classical | Opera | 2007-07-23 19:09:42 |
| 3 | C Sharp | 17 | 4 | 1 | Popular | Jazz | 2007-07-23 19:09:42 |
| 4 | C | 9 | 4 | 2 | Classical | Dance | 2007-07-23 19:09:42 |
| 5 | C++ | 24 | 2 | 5 | Classical | General | 2007-07-23 19:09:42 |
| 6 | Perl | 16 | 6 | 8 | Classical | Vocal | 2007-07-23 19:09:42 |
| 7 | Python | 2 | 25 | 6 | Popular | Blues | 2007-07-23 19:09:42 |
| 8 | Php | 32 | 3 | 10 | Popular | Jazz | 2007-07-23 19:09:42 |
| 9 | ASP.net | 12 | 15 | 13 | Popular | Country | 2007-07-23 19:09:42 |
| 10 | VB.net | 5 | 20 | 10 | Popular | New Age | 2007-07-23 19:09:42 |
| 11 | VC.net | 24 | 11 | 14 | Popular | New Age | 2007-07-23 19:09:42 |
| 12 | UML | 42 | 17 | 17 | Classical | General | 2007-07-23 19:09:42 |
| 13 | www.sqle.ru | 25 | 44 | 28 | Classical | Dance | 2007-07-23 19:09:42 |
| 14 | Oracle | 32 | 15 | 12 | Classical | General | 2007-07-23 19:09:42 |
| 15 | Pl/SQL | 20 | 10 | 5 | Classical | Opera | 2007-07-23 19:09:42 |
| 16 | Sql Server | 23 | 12 | 8 | Classical | General | 2007-07-23 19:09:42 |
+---------+----------------+---------+---------+----------+------------+----------+---------------------+
16 rows in set (0.00 sec)
mysql>
mysql>
mysql> SELECT Category, COUNT(*) AS Total
-> FROM Topic
-> WHERE Department="Popular"
-> GROUP BY Category;
+----------+-------+
| Category | Total |
+----------+-------+
| Blues | 1 |
| Country | 1 |
| Jazz | 2 |
| New Age | 2 |
| Rock | 1 |
+----------+-------+
5 rows in set (0.02 sec)
mysql>
mysql> drop table Topic;
Query OK, 0 rows affected (0.02 sec)
Use two aggregate functions in a select statement
mysql>
mysql>
mysql>
mysql> CREATE TABLE Employee(
-> id int,
-> first_name VARCHAR(15),
-> last_name VARCHAR(15),
-> start_date DATE,
-> end_date DATE,
-> salary FLOAT(8,2),
-> city VARCHAR(10),
-> description VARCHAR(15)
-> );
Query OK, 0 rows affected (0.05 sec)
mysql>
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description)
-> values (1,"Jason", "Martin", "19960725", "20060725", 1234.56, "Toronto", "Programmer");
Query OK, 1 row affected (0.01 sec)
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description)
-> values(2,"Alison", "Mathews", "19760321", "19860221", 6661.78, "Vancouver","Tester");
Query OK, 1 row affected (0.00 sec)
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description)
-> values(3,"James", "Smith", "19781212", "19900315", 6544.78, "Vancouver","Tester");
Query OK, 1 row affected (0.00 sec)
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description)
-> values(4,"Celia", "Rice", "19821024", "19990421", 2344.78, "Vancouver","Manager");
Query OK, 1 row affected (0.00 sec)
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description)
-> values(5,"Robert", "Black", "19840115", "19980808", 2334.78, "Vancouver","Tester");
Query OK, 1 row affected (0.00 sec)
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description)
-> values(6,"Linda", "Green", "19870730", "19960104", 4322.78,"New York", "Tester");
Query OK, 1 row affected (0.00 sec)
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description)
-> values(7,"David", "Larry", "19901231", "19980212", 7897.78,"New York", "Manager");
Query OK, 1 row affected (0.00 sec)
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description)
-> values(8,"James", "Cat", "19960917", "20020415", 1232.78,"Vancouver", "Tester");
Query OK, 1 row affected (0.00 sec)
mysql>
mysql> select * from Employee;
+------+------------+-----------+------------+------------+---------+-----------+-------------+
| id | first_name | last_name | start_date | end_date | salary | city | description |
+------+------------+-----------+------------+------------+---------+-----------+-------------+
| 1 | Jason | Martin | 1996-07-25 | 2006-07-25 | 1234.56 | Toronto | Programmer |
| 2 | Alison | Mathews | 1976-03-21 | 1986-02-21 | 6661.78 | Vancouver | Tester |
| 3 | James | Smith | 1978-12-12 | 1990-03-15 | 6544.78 | Vancouver | Tester |
| 4 | Celia | Rice | 1982-10-24 | 1999-04-21 | 2344.78 | Vancouver | Manager |
| 5 | Robert | Black | 1984-01-15 | 1998-08-08 | 2334.78 | Vancouver | Tester |
| 6 | Linda | Green | 1987-07-30 | 1996-01-04 | 4322.78 | New York | Tester |
| 7 | David | Larry | 1990-12-31 | 1998-02-12 | 7897.78 | New York | Manager |
| 8 | James | Cat | 1996-09-17 | 2002-04-15 | 1232.78 | Vancouver | Tester |
+------+------------+-----------+------------+------------+---------+-----------+-------------+
8 rows in set (0.00 sec)
mysql>
mysql>
mysql>
mysql> SELECT count(*), SUM(salary)
-> FROM employee;
+----------+-------------+
| count(*) | SUM(salary) |
+----------+-------------+
| 8 | 32574.02 |
+----------+-------------+
1 row in set (0.00 sec)
mysql>
mysql>
mysql>
mysql>
mysql> drop table Employee;
Query OK, 0 rows affected (0.00 sec)
mysql>