Mysql| Mysql函数,聚集函数的介绍与使用(Lower,Date,Mod,AVG,...)

关于MYSQL的函数

1.关于文本处理函数

-

SELECT vend_name,UPPER(vend_name) vend_name_upcase FROM vendors ORDER BY vend_name ASC;

+----------------+------------------+
| vend_name      | vend_name_upcase |
+----------------+------------------+
| ACME           | ACME             |
| Anvils R Us    | ANVILS R US      |
| Furball Inc.   | FURBALL INC.     |
| Jet Set        | JET SET          |
| Jouets Et Ours | JOUETS ET OURS   |
| LT Supplies    | LT SUPPLIES      |
+----------------+------------------+

SELECT customers.cust_name,customers.cust_contact FROM customers WHERE cust_contact = 'Y.Lie';

SELECT customers.cust_name,customers.cust_contact FROM customers WHERE SOUNDEX(cust_contact) = SOUNDEX('Y.Lie');

+-------------+--------------+
| cust_name   | cust_contact |
+-------------+--------------+
| Coyote Inc. | Y Lee        |
+-------------+--------------+

2.日期和时间处理函数

yyyy-mm-dd

orders表结构:
+------------+----------+------+-----+---------+----------------+
| Field      | Type     | Null | Key | Default | Extra          |
+------------+----------+------+-----+---------+----------------+
| order_num  | int(11)  | NO   | PRI | NULL    | auto_increment |
| order_date | datetime | NO   |     | NULL    |                |
| cust_id    | int(11)  | NO   | MUL | NULL    |                |
+------------+----------+------+-----+---------+----------------+

orders表中所有数据:
+-----------+---------------------+---------+
| order_num | order_date          | cust_id |
+-----------+---------------------+---------+
|     20005 | 2005-09-01 00:00:00 |   10001 |
|     20006 | 2005-09-12 00:00:00 |   10003 |
|     20007 | 2005-09-30 00:00:00 |   10004 |
|     20008 | 2005-10-03 00:00:00 |   10005 |
|     20009 | 2005-10-08 00:00:00 |   10001 |
+-----------+---------------------+---------+

SELECT * FROM orders WHERE order_date ='2005-09-01';

SELECT * FROM orders WHERE order_date ='2005-09-01  00:00:00';

+-----------+---------------------+---------+
| order_num | order_date          | cust_id |
+-----------+---------------------+---------+
|     20005 | 2005-09-01 10:00:00 |   10001 |
+-----------+---------------------+---------+

SELECT *  FROM orders WHERE DATE(order_date) ='2005-09-01';

SELECT * FROM orders WHERE YEAR(order_date) = 2005 AND MONTH(order_date) = 9;

3.数值处理函数

4.系统函数

聚集函数

*

COUNT(*)

(eg: SELECT SUM(item_price*quantity) AS total_price FROM orderitems WHERE order_num  = 20005;)

①AVG()函数用法:

SELECT AVG(prod_price) AS avg_price FROM products;

②COUNT()函数用法:

COUNT(*)

COUNT()

COUNT()

(*)

SELECT COUNT(*) AS num_cust FROM products;

SELECT COUNT(cust_email) AS num_cust FROM customers;

③MAX()函数用法:

SELECT MAX(prod_price) AS max_price FROM products;

④MIN()函数用法:

SELECT MIN(prod_price) AS min_price FROM products;

⑤SUM()函数用法:

SELECT SUM(quantity) AS items_ordered FROM orderitems WHERE  order_num  = 20005;

SELECT SUM(item_price*quantity) AS total_price FROM orderitems WHERE  order_num  = 20005;

聚集不同-用法:

SELECT AVG(DISTINCT prod_price) AS avg_price FROM products WHERE vend_id = 1003;

组合聚集-用法

SELECT COUNT(*) AS num_items, MIN(prod_price) AS price_min, MAX(prod_price) AS price_max, AVG(prod_price) AS price_avg FROM products;