mysql基础

SELECT篇

这是products表然后执行下面操作进行实验

这个是vendors表

检索数据:
1.检索所有的列 select * from products;
2.检索不同的值 select distinct vend_id from products;
3.检索限制结果 select prod_name from products limit 5;

排序检索数据:order by
1.排序数据 select prod_name from products order by prod_name;
2.多个列排序select prod_id,prod_price,prod_name from products order by prod_price,prod_name;
3.列位置排序select prod_id,prod_price,prod_name from products order by 2,3;
4.降序排列select prod_id,prod_price,prod_name from products order by prod_price DESC;


过滤数据:
1.使用WHERE子句
select prod_name,prod_price from products where prod_price=3.49;
以下为WHERE子句的操作符:
(1)检查单个值:where prod_price<=10;
(2)不匹配检查:SELECT vend_id, prod_name FROM Products WHERE vend_id <> 'DLL01';
(3)范围值检查:SELECT prod_name, prod_price FROM Products WHERE prod_price BETWEEN 5 AND 10;
(4)空值检查:

高级过滤:

1.组合的where子句

(1)AND操作符:select prod_id,prod_price,prod_name from products where vend_id='DLL01' and prod_price<=4 order by prod_id DESC;

(2)OR操作符:SELECT prod_name, prod_price FROM Products WHERE vend_id = 'DLL01' OR vend_id = ‘BRS01’;

(3)求值顺序,and的优先级高于or;

2.IN操作符

(1)指定语句执行范围:SELECT prod_name, prod_price FROM Products WHERE vend_id IN ( 'DLL01', 'BRS01' ) ORDER BY prod_name;

IN的优点:1.清楚直观,2.求值顺序易管理3.执行速度比where or更快4.最大优点可以动态建立where子句

3.NOT操作符

SELECT prod_name FROM Products WHERE NOT vend_id = 'DLL01' ORDER BY prod_name;

 通配符过滤:

LIKE操作符:

(1).%(%表示任何字符出现任意次数)

select prod_id,prod_name from products where prod_name like '%bean bag%';

注意:a.%可以匹配null之外的所有东西.b.很多DBMS都用空格填补字段的内容

(2)._(_和%区别是只匹配单个字符)

select prod_id,prod_name from products where prod_name like '__ inch teddy bear';

函数:略

汇总数据:

(1).COUNT()函数:确定表中行的数目:

SELECT COUNT(*) AS num_cust FROM products;

 注意:如果指定列名，则COUNT()函数会忽略指定列的值为空的行，但如果COUNT()函数中用的是星号（*），则不忽略。

如:SELECT COUNT(cust_email) AS num_cust FROM Customers;

(2).MIN(),AVG(),MAX(),SUM()函数:SELECT MIN(prod_price) AS min_price FROM Products;

(3).聚集不同的值:

SELECT AVG(DISTINCT prod_price) AS avg_price FROM Products WHERE vend_id = 'DLL01';

(4).组合聚集函数:

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

数据的分组

 1.group by创建分组

select vend_id, count(*) as count from products group by vend_id;

注意:a.GROUP BY子句必须出现在WHERE子句之后，ORDER BY子句之前

2.having过滤分组(where只可以过滤行不可以过滤分组)

select vend_id, count(*) as count from products group by vend_id having count(*)>2;

3.组排序

SELECT order_num, COUNT(*) AS items FROM OrderItems GROUP BY order_num HAVING COUNT(*) >= 3 ORDER BY items, order_num;

子查询:就是嵌套select语句

mysql> select cust_id
    -> from orders
    -> where order_num IN(select order_num from orderitems where prod_id='RGAN01');

(从里到外)

先执行select order_num from orderitems where prod_id='RGAN01'得到(20007,20008)

之后执行

SELECT cust_id
FROM Orders
WHERE order_num IN (20007,20008);

 联结表:

为什么用联结表?

将数据分解为多个表能更有效地存储，更方便地处理，并且可伸缩性更好

例子:看上面两个表

一个存储供应商信息，另一个存储产品信息。Vendors表包含所有供应商信息，每个供应商占一行，具有唯一的标
识。此标识称为主键，可以是供应商 ID 或任何其他唯一值。
Products表只存储产品信息，除了存储供应商 ID （Vendors表的主键）外，它不存储其他有关供应商的信息。Vendors表的主键将Vendors表
与Products表关联，利用供应商 ID 能从Vendors表中找出相应供应商的详细信息。

 好处:

1.供应商信息不重复，不会浪费时间和空间；
2.如果供应商信息变动，可以只更新Vendors表中的单个记录，相关表中的数据不用改动；
3.由于数据不重复，数据显然是一致的，使得处理数据和生成报表更简单。

关系数据可以有效地存储，方便地处理,可伸缩性更强

用法:

1.创建联结

select vend_name,prod_name,prod_price from vendors,products where vendors.vend_id = products.vend_id;

2.内联结

SELECT vend_name, prod_name, prod_price FROM Vendors INNER JOIN Products ON Vendors.vend_id = Products.vend_id;(效果以上面相同)

3.联结多个表(联结的表约多性能越差,所以要减少不必要的表)

创建高级联结

 1.给表也可以取别名

2.自联结

mysql> select cust_id,cust_name,cust_contact
    -> from customers
    -> where cust_name=(select cust_name from customers where cust_contact='JIM Jones')
    -> ;
+------------+-----------+------------------+
| cust_id     | cust_name | cust_contact      |
+------------+-----------+------------------+
| 1000000003 | Fun4All    | Jim Jones         |
| 1000000004 | Fun4All    | Denise L. Stephens |
+------------+-----------+------------------+
2 rows in set

mysql> select c1.cust_id,c1.cust_name,c1.cust_contact
    -> from customers as c1,customers as c2
    -> where c1.cust_name=c2.cust_name
    -> and c2.cust_contact='Jim Jones'
    -> ;
+------------+-----------+------------------+
| cust_id     | cust_name | cust_contact      |
+------------+-----------+------------------+
| 1000000003 | Fun4All    | Jim Jones         |
| 1000000004 | Fun4All    | Denise L. Stephens |
+------------+-----------+------------------+
2 rows in set

 自然联结

外联结

 使用带聚集函数联结

mysql> SELECT Customers.cust_id,
COUNT(Orders.order_num) AS num_ord
FROM Customers INNER JOIN Orders
ON Customers.cust_id = Orders.cust_id
GROUP BY Customers.cust_id;
+------------+---------+
| cust_id     | num_ord |
+------------+---------+
| 1000000001 |       2 |
| 1000000003 |       1 |
| 1000000004 |       1 |
| 1000000005 |       1 |
+------------+---------+
4 rows in set



mysql> SELECT Customers.cust_id,
COUNT(Orders.order_num) AS num_ord
FROM Customers LEFT OUTER JOIN Orders
ON Customers.cust_id = Orders.cust_id
GROUP BY Customers.cust_id;
+------------+---------+
| cust_id     | num_ord |
+------------+---------+
| 1000000001 |       2 |
| 1000000002 |       0 |
| 1000000003 |       1 |
| 1000000004 |       1 |
| 1000000005 |       1 |
+------------+---------+
5 rows in set



mysql> SELECT Customers.cust_id,
COUNT(Orders.order_num) AS num_ord
FROM Customers right OUTER JOIN Orders
ON Customers.cust_id = Orders.cust_id
GROUP BY Customers.cust_id;
+------------+---------+
| cust_id     | num_ord |
+------------+---------+
| 1000000001 |       2 |
| 1000000003 |       1 |
| 1000000004 |       1 |
| 1000000005 |       1 |
+------------+---------+
4 rows in set

组合查询

1.使用union

mysql> SELECT cust_name, cust_contact, cust_email
FROM Customers
WHERE cust_state IN ('IL','IN','MI')
UNION
SELECT cust_name, cust_contact, cust_email
FROM Customers
WHERE cust_name = 'Fun4All';
+--------------+------------------+----------------------+
| cust_name    | cust_contact      | cust_email            |
+--------------+------------------+----------------------+
| Village Toys   | John Smith        | sales@villagetoys.com  |
| Fun4All       | Jim Jones         | jjones@fun4all.com     |
| The Toy Store | Kim Howard       | NULL                 |
| Fun4All       | Denise L. Stephens | dstephens@fun4all.com |
+--------------+------------------+----------------------+
4 rows in set

union的使用规则

1.UNION必须由两条或两条以上的SELECT语句组成，语句之间用关键字UNION分隔（因此，如果组合四条SELECT语句，将要使用三个UNION关键字）。
2.UNION中的每个查询必须包含相同的列、表达式或聚集函数（不过，各个列不需要以相同的次序列出）。
3.列数据类型必须兼容：类型不必完全相同，但必须是 DBMS 可以隐含转换的类型（例如，不同的数值类型或不同的日期类型）。

包含或取消重复的行,更上面的作比较

SELECT cust_name, cust_contact, cust_email
FROM Customers
WHERE cust_state IN ('IL','IN','MI')
UNION ALL
SELECT cust_name, cust_contact, cust_email
FROM Customers
WHERE cust_name = 'Fun4All';

+--------------+------------------+----------------------+
| cust_name    | cust_contact      | cust_email            |
+--------------+------------------+----------------------+
| Village Toys   | John Smith        | sales@villagetoys.com  |
| Fun4All       | Jim Jones         | jjones@fun4all.com     |
| The Toy Store | Kim Howard       | NULL                 |
| Fun4All       | Jim Jones         | jjones@fun4all.com     |
| Fun4All       | Denise L. Stephens | dstephens@fun4all.com |
+--------------+------------------+----------------------+

对组合的结果排序

SELECT语句的输出用ORDER BY子句排序。在用UNION组合查询时，只能使用一条ORDER BY子句，它必须位于最后一条SELECT语句之后。对于结果
集，不存在用一种方式排序一部分，而又用另一种方式排序另一部分的情况，因此不允许使用多条ORDER BY子句。

mysql> SELECT cust_name, cust_contact, cust_email
FROM Customers
WHERE cust_state IN ('IL','IN','MI')
UNION
SELECT cust_name, cust_contact, cust_email
FROM Customers
WHERE cust_name = 'Fun4All'
ORDER BY cust_name, cust_contact;
+--------------+------------------+----------------------+
| cust_name    | cust_contact      | cust_email            |
+--------------+------------------+----------------------+
| Fun4All       | Denise L. Stephens | dstephens@fun4all.com |
| Fun4All       | Jim Jones         | jjones@fun4all.com     |
| The Toy Store | Kim Howard       | NULL                 |
| Village Toys   | John Smith        | sales@villagetoys.com  |
+--------------+------------------+----------------------+
4 rows in set

INSERT(数据插入)

这个是customers表

下面进行插入操作

 如果这样插入,就一定要按照表头的顺序插入

mysql> INSERT INTO Customers
VALUES('199808041011',
'zoulingjin',
'123 Any Street',
'HUNAN',
'ZZ',
'11111',
'CHINA',
NULL,
NULL);
Query OK, 1 row affected

下面的操作具有稳定性

mysql> INSERT INTO Customers(cust_id,
cust_contact,
cust_email,
cust_name,
cust_address,
cust_city,
cust_state,
cust_zip)
VALUES('1000000006',
NULL,
NULL,
'Toy Land',
'123 Any Street',
'New York',
'NY',
'11111');
Query OK, 1 row affected

插入检索的数据

INSERT INTO Customers(cust_id,
cust_contact,
cust_email,
cust_name,
cust_address,
cust_city,
cust_state,
cust_zip,
cust_country)
SELECT cust_id,
cust_contact,
cust_email,
cust_name,
cust_address,
cust_city,
cust_state,
cust_zip,
cust_country
FROM CustNew;

将一个表复制到另个新表中

mysql> create table zoutable as
    -> select * from customers;
Query OK, 7 rows affected
Records: 7  Duplicates: 0  Warnings: 0

UPDATE AND DELETE

update语法

mysql> UPDATE customers
    -> set cust_email='zou@qq.com'
    -> where cust_id='1000000005'
    -> ;
Query OK, 1 row affected
Rows matched: 1  Changed: 1  Warnings: 0

在更新多个列时,是需要一个set命令.每个"列=值"对之间用逗号分割

要删除一个值时,可以设置set 为null

delete语法

mysql> delete from customers
    -> where cust_id='1000000006'
    -> ;
Query OK, 1 row affected

表的操作

step1:创建表

CREATE TABLE Persons
(
Id int(4) NOT NULL,
Name varchar(255) NOT NULL,
Password varchar(255),
PRIMARY KEY (Id)
);

CREATE TABLE `player` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` char(20) NOT NULL DEFAULT '' COMMENT '站点名称',
  `area` varchar(255) NOT NULL DEFAULT '',
  `alexa` int(11) NOT NULL DEFAULT '0' COMMENT 'Alexa 排名',
  `team` char(10) NOT NULL DEFAULT '' COMMENT '国家',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=utf8;



INSERT INTO `player` VALUES ('1', 'Leonard', '美国圣安东尼奥', '95', '马刺'), 
('2', 'Curry', '美国金州', '94', '勇士'), 
('3', 'Durant', '美国金州', '93', '勇士'), 
('4', 'James', '美国克利夫兰', '92', '骑士'), 
('5', 'Lillard', '美国奥克兰', '89', '开拓者');

高级SQL特性