SQL必知必会 14-22（完）

博主依然不想打字，又向你仍来了一堆代码。。。

13（续）

在SELECT中用COUNT（）以及联合

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 cust_id;
+------------+---------+
| cust_id    | num_ord |
+------------+---------+
| 1000000001 |       2 |
| 1000000003 |       1 |
| 1000000004 |       1 |
| 1000000005 |       1 |
+------------+---------+
4 rows in set (0.00 sec)

14、组合查询

UNION，UNION ALL（显示重复行）；

多条SELECT合并为一个查询输出；

必须有相同的列数，顺序可以不一样但数据类型要可以转换的；

UNION ALL显示重复行，除此以外的使用，都可以用WHERE来替换；

ORDER BY放在最后一句，只需要一句；

不过事实证明，顺序还是会有影响的 。。。

mysql> SELECT cust_name,cust_contact,cust_emali
    -> FROM customers
    -> WHERE cust_state IN ('IL','IN','MI');
ERROR 1054 (42S22): Unknown column 'cust_emali' in 'field list'
mysql> SELECT cust_name,cust_contact,cust_email
    -> FROM customers
    -> WHERE cust_state IN ('IL','IN','MI');
+---------------+--------------+-----------------------+
| 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                  |
+---------------+--------------+-----------------------+
3 rows in set (0.00 sec)

mysql> SELECT cust_name,cust_email,cust_contact
    -> FROM customers
    -> WHERE cust_name='Fun4All';
+-----------+-----------------------+--------------------+
| cust_name | cust_email            | cust_contact       |
+-----------+-----------------------+--------------------+
| Fun4All   | jjones@fun4all.com    | Jim Jones          |
| Fun4All   | dstephens@fun4all.com | Denise L. Stephens |
+-----------+-----------------------+--------------------+
2 rows in set (0.00 sec)

mysql> SELECT cust_name,cust_contact,cust_email
    -> FROM customers
    -> WHERE cust_state IN ('IL','IN','MI')
    -> UNION
    -> SELECT cust_name,cust_email,cust_contact
    -> 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       | jjones@fun4all.com    | Jim Jones             |
| Fun4All       | dstephens@fun4all.com | Denise L. Stephens    |
+---------------+-----------------------+-----------------------+
5 rows in set (0.00 sec)

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 (0.00 sec)

mysql> 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 |
+---------------+--------------------+-----------------------+
5 rows in set (0.00 sec)

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_name     | cust_contact       | cust_email            |
+---------------+--------------------+-----------------------+
| Fun4All       | Jim Jones          | jjones@fun4all.com    |
| Fun4All       | Denise L. Stephens | dstephens@fun4all.com |
| The Toy Store | Kim Howard         | NULL                  |
| Village Toys  | John Smith         | sales@villagetoys.com |
+---------------+--------------------+-----------------------+
4 rows in set (0.00 sec)

15、插入数据

INSERT,INSERT INTO,INSERT SELECT,SELECT INTO

插入完整的行，插入行的一部分，插入某些查询结果；

用INSERT INTO替代INSERT，提高可移植性；

注意格式写法；

最好写上列名；

INSERT一般只能插入一条，INSERT SELECT是个例外；

SELECT INTO实现复制（MySQL和Oracle的有所不同）

mysql> CREATE TABLE custNew(
    -> cust_id INT PRIMARY KEY,
    -> cust_contact VARCHAR(32),
    -> cust_email VARCHAR(32),
    -> cust_name VARCHAR(32),
    -> cust_address VARCHAR(64),
    -> cust_city VARCHAR(16),
    -> cust_state VARCHAR(16),
    -> cust_zip SMALLINT,
    -> cust_country VARCHAR(16)
    -> );
Query OK, 0 rows affected (0.21 sec)

mysql> INSERT INTO custNew(
    ->   cust_id,
    ->   cust_email,
    ->   cust_name,
    ->   cust_zip,
    ->   cust_country,
    ->   cust_city)
    -> VALUES(
    ->   1021,
    ->   'liangbocv@126.com',
    ->   'Andy Liang',
    ->   610000,
    ->   'China',
    ->   'Chengdu');
Query OK, 1 row affected, 1 warning (0.04 sec)

mysql> INSERT INTO customers(
    ->   cust_id,
    ->   cust_email,
    ->   cust_name,
    ->   cust_zip,
    ->   cust_country,
    ->   cust_city)
    -> SELECT cust_id,
    ->   cust_email,
    ->   cust_name,
    ->   cust_zip,
    ->   cust_country,
    ->   cust_city
    -> FROM custNew;
Query OK, 1 row affected (0.03 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> SELECT * FROM customers;
+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+
| cust_id    | cust_name     | cust_address         | cust_city | cust_state | cust_zip | cust_country | cust_contact       | cust_email            |
+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+
| 1000000001 | Village Toys  | 200 Maple Lane       | Detroit   | MI         | 44444    | USA          | John Smith         | sales@villagetoys.com |
| 1000000002 | Kids Place    | 333 South Lake Drive | Columbus  | OH         | 43333    | USA          | Michelle Green     | NULL                  |
| 1000000003 | Fun4All       | 1 Sunny Place        | Muncie    | IN         | 42222    | USA          | Jim Jones          | jjones@fun4all.com    |
| 1000000004 | Fun4All       | 829 Riverside Drive  | Phoenix   | AZ         | 88888    | USA          | Denise L. Stephens | dstephens@fun4all.com |
| 1000000005 | The Toy Store | 4545 53rd Street     | Chicago   | IL         | 54545    | USA          | Kim Howard         | NULL                  |
| 1021       | Andy Liang    | NULL                 | Chengdu   | NULL       | 32767    | China        | NULL               | liangbocv@126.com     |
+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+
6 rows in set (0.00 sec)

mysql> CREATE TABLE custcopy(
    -> cust_id VARCHAR(16),
    -> cust_contact VARCHAR(32),
    -> cust_email VARCHAR(32),
    -> cust_name VARCHAR(32),
    -> cust_address VARCHAR(64),
    -> cust_city VARCHAR(16),
    -> cust_state VARCHAR(16),
    -> cust_zip VARCHAR(16),
    -> cust_country VARCHAR(16)
    -> );
Query OK, 0 rows affected (0.26 sec)

mysql> SELECT *
    -> INTO custcopy
    -> FROM customers;
ERROR 1327 (42000): Undeclared variable: custcopy
mysql> CREATE TABLE custcopy2 AS
    -> SELECT *
    -> FROM customers;
Query OK, 6 rows affected (0.41 sec)
Records: 6  Duplicates: 0  Warnings: 0

16、更新和删除数据

UPADTE,DELETE

容易使用，但请小心使用；（没有UNDO！！！）

UPDATE为null=DELETE；

一些习惯：一定带WHERE ,避免对整个表有影响；

对数据做更改时，请先SELECT查询一下，看对象是否没错；

确保每个表有主键

mysql> SELECT cust_id,cust_address,cust_state
    -> FROM customers
    -> WHERE cust_id='';
+---------+--------------+------------+
| cust_id | cust_address | cust_state |
+---------+--------------+------------+
| 1021    | NULL         | NULL       |
+---------+--------------+------------+
1 row in set (0.00 sec)

mysql> UPDATE customers
    -> SET cust_address='2006 Xiyuan Ave.',
    ->     cust_state='SC'
    -> WHERE cust_id='';
Query OK, 1 row affected (0.02 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> SELECT cust_id,cust_address,cust_state
    -> FROM customers
    -> WHERE cust_id='';
+---------+------------------+------------+
| cust_id | cust_address     | cust_state |
+---------+------------------+------------+
| 1021    | 2006 Xiyuan Ave. | SC         |
+---------+------------------+------------+
1 row in set (0.00 sec)

mysql> UPDATE customers
    -> SET cust_email=NULL
    -> WHERE cust_id='';
Query OK, 1 row affected (0.03 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> DELETE FROM customers
    -> WHERE cust_id='';
Query OK, 1 row affected (0.08 sec)

17、创建和操作表

CREATE,DROP,ALTER,RENAME,DEFAULT

更新表，和更新数据一样小心，做好备份；

重命名不太一样，mysql是RENAME

mysql> ALTER TABLE custcopy2
    -> ADD cust_gender VARCHAR(8);
Query OK, 0 rows affected (0.41 sec)
Records: 0  Duplicates: 0  Warnings: 0
mysql> SELECT CURRENT_DATE();
+----------------+
| CURRENT_DATE() |
+----------------+
| 2016-08-10     |
+----------------+
1 row in set (0.16 sec)

mysql> ALTER TABLE custcopy2
    -> ADD add_time TIMESTAMP DEFAULT CURRENT_TIMESTAMP;
Query OK, 0 rows affected (0.46 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> DROP TABLE custcopy;
Query OK, 0 rows affected (0.13 sec)

mysql> RENAME TABLE custcopy2 TO custcopy;
Query OK, 0 rows affected (0.10 sec)

18、使用视图

VIEW

view实际上就是个虚拟的表，只包含使用时动态检索数据的查询；

使用view，有利于代码重用，保护数据，简化操作；

视图名也要唯一；可以嵌套，一般禁止ORDER BY；

用于简化复杂联结，格式化输出，过滤不想要的数据等；

WHERE语句会自动合并

mysql> CREATE VIEW shit AS
    -> SELECT cust_name,cust_id,cust_contact,cust_address
    -> FROM customers
    -> ;
Query OK, 0 rows affected (0.07 sec)

mysql> SELECT cust_name,cust_address
    -> FROM shit
    -> WHERE cust_id='';
Empty set (0.00 sec)

mysql> SELECT * FROM customers;
+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+
| cust_id    | cust_name     | cust_address         | cust_city | cust_state | cust_zip | cust_country | cust_contact       | cust_email            |
+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+
| 1000000001 | Village Toys  | 200 Maple Lane       | Detroit   | MI         | 44444    | USA          | John Smith         | sales@villagetoys.com |
| 1000000002 | Kids Place    | 333 South Lake Drive | Columbus  | OH         | 43333    | USA          | Michelle Green     | NULL                  |
| 1000000003 | Fun4All       | 1 Sunny Place        | Muncie    | IN         | 42222    | USA          | Jim Jones          | jjones@fun4all.com    |
| 1000000004 | Fun4All       | 829 Riverside Drive  | Phoenix   | AZ         | 88888    | USA          | Denise L. Stephens | dstephens@fun4all.com |
| 1000000005 | The Toy Store | 4545 53rd Street     | Chicago   | IL         | 54545    | USA          | Kim Howard         | NULL                  |
+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+
5 rows in set (0.00 sec)

mysql> SELECT cust_name,cust_address
    -> FROM shit
    -> WHERE cust_id='';
+--------------+----------------+
| cust_name    | cust_address   |
+--------------+----------------+
| Village Toys | 200 Maple Lane |
+--------------+----------------+
1 row in set (0.00 sec)

mysql> CREATE VIEW hasEmail AS
    -> SELECT cust_name,cust_id,cust_email
    -> FROM customers
    -> WHERE cust_email IS NOT NULL;
Query OK, 0 rows affected (0.06 sec)

mysql> SELECT *
    -> FROM hasEmail
    -> WHERE cust_name='Fun4All';
+-----------+------------+-----------------------+
| cust_name | cust_id    | cust_email            |
+-----------+------------+-----------------------+
| Fun4All   | 1000000003 | jjones@fun4all.com    |
| Fun4All   | 1000000004 | dstephens@fun4all.com |
+-----------+------------+-----------------------+
2 rows in set (0.00 sec)

19、存储过程

PROCEDURE,DELIMITER,CALL

以下引用自百度：存储过程（Stored Procedure）是在大型数据库系统中，一组为了完成特定功能的SQL 语句集，存储在数据库中，经过第一次编译后再次调用不需要再次编译，用户通过指定存储过程的名字并给出参数（如果该存储过程带有参数）来执行它。存储过程是数据库中的一个重要对象，任何一个设计良好的数据库应用程序都应该用到存储过程。

有点好玩又有点繁琐的。。。

mysql> DELIMITER &&
mysql> CREATE PROCEDURE showAll()
    ->   BEGIN
    ->   SELECT * FROM customers;
    -> END &&
Query OK, 0 rows affected (0.04 sec)

mysql> CALL showAll();
+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+
| cust_id    | cust_name     | cust_address         | cust_city | cust_state | cust_zip | cust_country | cust_contact       | cust_email            |
+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+
| 1000000001 | Village Toys  | 200 Maple Lane       | Detroit   | MI         | 44444    | USA          | John Smith         | sales@villagetoys.com |
| 1000000002 | Kids Place    | 333 South Lake Drive | Columbus  | OH         | 43333    | USA          | Michelle Green     | NULL                  |
| 1000000003 | Fun4All       | 1 Sunny Place        | Muncie    | IN         | 42222    | USA          | Jim Jones          | jjones@fun4all.com    |
| 1000000004 | Fun4All       | 829 Riverside Drive  | Phoenix   | AZ         | 88888    | USA          | Denise L. Stephens | dstephens@fun4all.com |
| 1000000005 | The Toy Store | 4545 53rd Street     | Chicago   | IL         | 54545    | USA          | Kim Howard         | NULL                  |
+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+
5 rows in set (0.00 sec)

Query OK, 0 rows affected (0.08 sec)

mysql> DELIMITER $
mysql> CREATE PROCEDURE getID(
    ->   IN id VARCHAR(32))
    ->   BEGIN
    ->   SELECT *
    ->   FROM customers
    ->   WHERE cust_id=id;
    -> END $
Query OK, 0 rows affected (0.00 sec)

mysql> CALL getID('')$
+------------+--------------+----------------+-----------+------------+----------+--------------+--------------+-----------------------+
| cust_id    | cust_name    | cust_address   | cust_city | cust_state | cust_zip | cust_country | cust_contact | cust_email            |
+------------+--------------+----------------+-----------+------------+----------+--------------+--------------+-----------------------+
| 1000000001 | Village Toys | 200 Maple Lane | Detroit   | MI         | 44444    | USA          | John Smith   | sales@villagetoys.com |
+------------+--------------+----------------+-----------+------------+----------+--------------+--------------+-----------------------+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.03 sec)

mysql> DELIMITER ;

注意输入参数那里的变化。

20、事务管理

TRANSACTION,COMMIT,ROLLBACK,SAVEPOINT

用来维护数据库的完整性，保证成批的SQL操作要么完全执行，要么完全不执行；

保留点越多越好，更好的是形成习惯~

mysql> BEGIN;
Query OK, 0 rows affected (0.00 sec)

mysql> SAVEPOINT begin;
Query OK, 0 rows affected (0.00 sec)

mysql> INSERT INTO customers(cust_name,cust_country)
    ->  VALUES('Andy Liang','China');
Query OK, 1 row affected, 1 warning (0.00 sec)

mysql> ROLLBACK TO begin;
Query OK, 0 rows affected (0.04 sec)

mysql> COMMIT;
Query OK, 0 rows affected (0.00 sec)

MySQL是一步步来的，就是慢慢监督的一样。

21、使用游标

CURSOR

略。。。。（老子做web不想用游标，你来打我啊

22、约束，索引，触发器

约束:

PRIMARY KEY,UNIQUE,REFERENCES,ALTER,CONSTRAINT,CHECK

主键：值互异，NOT NULL，不修改/更新，不重用，每个表仅能有一个主键，可以用来定义外键（举例：id

唯一：值互异，可以有NULL，可修改/更新，可重用，可有多个唯一键，不能用来定义外键

外键：两个表，确定子表某一列的合法性

检查约束：CHECK，灵活约束

mysql> CREATE TABLE test(
    -> id SMALLINT NOT NULL PRIMARY KEY AUTO_INCREMENT,
    -> socialid VARCHAR(64) UNIQUE,
    -> cust_id VARCHAR(16) NOT NULL REFERENCES customers(cust_id),
    -> quantity SMALLINT CHECK (quantity>0),
    -> gender VARCHAR(8) CHECK (gender LIKE '[MF]')
    -> );
Query OK, 0 rows affected (0.20 sec)

另外，用ALTER语句再对表进行更改操作

ALTER TABLE test
ADD CONSTRAINT PRIMARY KEY (cust_id);

ALTER TABLE test
ADD CONSTRAINT UNIQUE KEY (id);

ALTER TABLE test
ADD CONSTRAINT
FOREIGN KEY (cust_id) REFERENCES customers (cust_id);

ALTER TABLE test
ADD CONSTRAINT CHECK (quantity<1000);

索引：

INDEX

搜索某些列的效率提高；

请动态的创建索引——数据库在不断更新，索引效率在变化；索引效率提升的代价是插入等操作性能的牺牲；大量空间的使用；

mysql> CREATE INDEX prod_name_id
    -> ON PRODUCTS (prod_name);
Query OK, 0 rows affected (0.31 sec)
Records: 0  Duplicates: 0  Warnings: 0

触发器：

TRIGGER

在特定的数据库活动发生时自动执行；

一般用途：保证数据一致（全大写等），联动（log的记录）等；

约束要比触发器快，尽量用约束；

完！！（对，这里又灭有代码了