1.Drop
DROP [TEMPORARY] TABLE [IF EXISTS]
tbl_name [, tbl_name] ...
[RESTRICT | CASCADE]
示例：DROP TABLE table;
2.vchar(256)
在创建表时正确的数据类型为char(256)，而且最大长度限制为255，改为char(255)
3.PRIMARY KEY
在一个表中，为PRIMARY KEY的字段只能有一个
4.建表示例
mysql> create table MyClass(
> id int(4) not null primary key auto_increment,
> name char(20) not null,
> sex int(4) not null default '0',
> degree double(16,2));
5.防止字段重复
ALTER TABLE `TableName`
ADD UNIQUE INDEX IndexName(`FieldName`);
6.SHOW
show databases;
show tables from db_name;
show columns from table_name from db_name;
show index from talbe_name [from db_name];
show status;
show variables;
show [full] processlist;
show table status [from db_name];
show grants for user;
7.事务加X锁(排他锁)
SET TRANSACTION ISOLATION LEVEL REPEATABLE READ BEGIN TRAN
SELECT * FROM bigtable
UPDATE bigtable
SET col = 0
WHERE keycolumn = 100
8.事务
begin 开始事务
commit 提交事务
rollback 回滚事务
9.引擎与自动回滚
我的MYSQL默认引擎为InnoDB
我们可以通过SHOW ENGINES；查看
InnoDB默认自动回滚事务，参考http://www.yiibai.com/mysql5/constraints.html
10.UPDATE语句
单表Update
1 UPDATE [LOW_PRIORITY] [IGNORE] tbl_name
2 SET col_name1=expr1 [, col_name2=expr2 ...]
3 [WHERE where_definition]
4 [ORDER BY ...]
5 [LIMIT row_count]
多表Update
1 UPDATE [LOW_PRIORITY] [IGNORE] table_references
2 SET col_name1=expr1 [, col_name2=expr2 ...]
3 [WHERE where_definition]
