1、创建临时表
临时表是一张表，用来临时保存一些数据
特点：
只对创建该临时表的用户可见；
当会话结束时，MySQL自动删除临时表。
临时表的核心：建表和删表消耗资源极其少
创建临时表的基本格式：
CREATE TEMPORARY TABLE tbl_name(……);
①创建的临时表在当前会话，正常使用
②断开连接，再重新连接后执行查询，抛出异常：
错误代码： 1146
Table ‘db_name.temtbl_name’ doesn‘t exist。//该临时表在会话结束的时候被系统删除。
注意：用户可以创建一个和已有的普通表名字相同的临时表。
在这种情况下，
该用户只能看到临时表而看不见同名的普通表；
当临时表被删除后，才可以看到普通表。
示例：使用相同的名字创建一个普通表和临时表
mysql> create table test_table(num int);
Query OK, 0 rows affected (0.12 sec)
mysql> insert into test_table values(1);
Query OK, 1 row affected (0.04 sec)
mysql> create temporary table test_table(num int,name varchar(20));
Query OK, 0 rows affected (0.04 sec)
mysql> insert into test_table values(2,'临时表测试');
Query OK, 1 row affected (0.00 sec)
mysql> select * from test_table;
+------+-----------------+
| num | name |
+------+-----------------+
| 2 | 临时表测试 |
+------+-----------------+
1 row in set (0.00 sec)
mysql> drop table test_table;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from test_table;
+------+
| num |
+------+
| 1 |
+------+
1 row in set (0.00 sec)
Q：当创建表时，如果表已经存在了，则MySQL会返回出错消息，我们不希望看到报错的信息，该如何处理？
A：添加IF NOT EXISTS选项，则强制不显示这个出错消息；但是，语句执行失败---建表失败。
mysql> create table if not exists PLAYERS(id int(5),name varchar(20));
Query OK, 0 rows affected, 1 warning (0.00 sec)
mysql> show warnings;
+-------+------+--------------------------------+
| Level | Code | Message |
+-------+------+--------------------------------+
| Note | 1050 | Table 'PLAYERS' already exists |
+-------+------+--------------------------------+
1 row in set (0.00 sec)
mysql> show tables;
+-------------------+
| Tables_in_TENNIS |
+-------------------+
| COMMITTEE_MEMBERS |
| MATCHES |
| PENALTIES |
| PLAYERS |
| TEAMS |
| test_table |
+-------------------+
6 rows in set (0.00 sec)
2、根据已有的表来创建新表
语法1：只想拷贝表结构
CREATE TABLE new_tbl LIKE orig_tbl;
将从源表复制列名、数据类型、大小、非空约束以及索引；而表的内容以及其它约束不会复制，新表是一张空表。
mysql> desc TEAMS;
+----------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+---------+------+-----+---------+-------+
| TEAMNO | int(11) | NO | PRI | NULL | |
| PLAYERNO | int(11) | NO | | NULL | |
| DIVISION | char(6) | NO | | NULL | |
+----------+---------+------+-----+---------+-------+
3 rows in set (0.00 sec)
mysql> create table copy_TEAMS like TEAMS;
Query OK, 0 rows affected (0.11 sec)
mysql> select * from copy_TEAMS;
Empty set (0.00 sec)
mysql> desc copy_TEAMS;
+----------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+---------+------+-----+---------+-------+
| TEAMNO | int(11) | NO | PRI | NULL | |
| PLAYERNO | int(11) | NO | | NULL | |
| DIVISION | char(6) | NO | | NULL | |
+----------+---------+------+-----+---------+-------+
3 rows in set (0.00 sec)
语法2：根据SELECT子查询的拷贝
CREATE TABLE new_tbl [AS] SELECT {*|column,...} FROM orig_tbl;
新表的结构由select列表决定；同时把查询返回的结果集中的行插入到目标表中；只能把非空约束带入到新表中(在有的时候就会显得很鸡肋了)，也不会复制索引
mysql> create table p_m
-> as
-> select a.NAME,a.SEX,b.MATCHNO,b.WON,b.LOST
-> from PLAYERS a,MATCHES b
-> where a.PLAYERNO=b.PLAYERNO;
Query OK, 13 rows affected (0.15 sec)
Records: 13 Duplicates: 0 Warnings: 0
mysql> select * from p_m;
+-----------+-----+---------+-----+------+
| NAME | SEX | MATCHNO | WON | LOST |
+-----------+-----+---------+-----+------+
| Parmenter | M | 1 | 3 | 1 |
| Parmenter | M | 2 | 2 | 3 |
| Parmenter | M | 3 | 3 | 0 |
| Baker | M | 4 | 3 | 2 |
| Hope | M | 5 | 0 | 3 |
| Everett | M | 6 | 1 | 3 |
| Brown | M | 7 | 3 | 0 |
| Newcastle | F | 8 | 0 | 3 |
| Collins | F | 9 | 3 | 2 |
| Moorman | F | 10 | 3 | 2 |
| Bailey | F | 11 | 2 | 3 |
| Bailey | F | 12 | 1 | 3 |
| Newcastle | F | 13 | 0 | 3 |
+-----------+-----+---------+-----+------+
13 rows in set (0.00 sec)
通过根据已有表来创建新表，添加选项temporary，创建临时副本用来做练习最合适：表内容可一样，会话结束，临时表自动删除，原始表中的内容不受任何影响。
注意：
如果在表名后面指定的列名和原始表中的列名相同，则可以改变列的大小和非空约束；
如果在表名后面指定的列名和原始表中的列名不同，则它作为一个新的列。
mysql> select * from TEAMS;
+--------+----------+----------+
| TEAMNO | PLAYERNO | DIVISION |
+--------+----------+----------+
| 1 | 6 | first |
| 2 | 27 | second |
+--------+----------+----------+
mysql> CREATE TABLE teams_copy
-> (
-> teamno INTEGER NOT NULL PRIMARY KEY,
-> playerno INTEGER NULL,
-> division char(10) NOT NULL,
-> coach varchar(20)
-> )
-> as
-> select * from TEAMS;
Query OK, 2 rows affected (0.11 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> select * from teams_copy;
+-------+--------+----------+----------+
| coach | TEAMNO | PLAYERNO | DIVISION |
+-------+--------+----------+----------+
| NULL | 1 | 6 | first |
| NULL | 2 | 27 | second |
+-------+--------+----------+----------+