Mysql的常用用法

一、mysql中limit的用法详解[数据分页常用]

在我们使用查询语句的时候，经常要返回前几条或者中间某几行数据，这个时候怎么办呢？不用担心，mysql已经为我们提供了这样一个功能。

SELECT * FROM table LIMIT [offset,] rows | rows OFFSET offset

LIMIT 子句可以被用于强制 SELECT 语句返回指定的记录数。LIMIT 接受一个或两个数字参数。参数必须是一个整数常量。如果给定两个参数，第一个参数指定第一个返回记录行的偏移量，第二个参数指定返回记录行的最大数目。初始记录行的偏移量是 0(而不是 1)：为了与 PostgreSQL 兼容，MySQL 也支持句法： LIMIT # OFFSET #。

mysql> SELECT * FROM table LIMIT 5,10; // 检索记录行 6-15

//为了检索从某一个偏移量到记录集的结束所有的记录行，可以指定第二个参数为 -1：

mysql> SELECT * FROM table LIMIT 95,-1; // 检索记录行 96-last.

//如果只给定一个参数，它表示返回最大的记录行数目：

mysql> SELECT * FROM table LIMIT 5; //检索前 5 个记录行

//换句话说，LIMIT n 等价于 LIMIT 0,n。

二、mysql中sql文件的编辑和如何导入导出sql文件

1、MYSQL中SQL文件的编辑：

　　随便使用一种编辑器都可以编辑，保存的sql文件后缀为：.sql。

　　sql中的内容参考下面例子，创建数据库： job5db

DROP DATABASE IF EXISTS job5db;

CREATE DATABASE job5db DEFAULT CHARACTER SET utf8;

USE job5db;

##创建用户表

CREATE TABLE t_user (

   user_id   INT AUTO_INCREMENT PRIMARY KEY,

   user_name VARCHAR(30),

   password  VARCHAR(32)

)ENGINE=InnoDB; 

##创建投票记录表

CREATE TABLE t_vote (

   vote_id  INT AUTO_INCREMENT PRIMARY KEY,

   vote_topic   VARCHAR(30),

   vote_state   VARCHAR(10),

   vote_max_can_select  INT,

   vote_total_count  INT,

   vote_total_option_count  INT,

   create_time timestamp default now(),

   start_time datetime,

   end_time datetime

)ENGINE=InnoDB; 

##创建投票项表

CREATE TABLE t_option (

   option_id  INT AUTO_INCREMENT PRIMARY KEY,

   option_name   INT,

   option_count  VARCHAR(23),

   vote_id INT,

   foreign key(vote_id) references t_vote(vote_id)

)ENGINE=InnoDB; 

##插入初始化数据

INSERT INTO t_user (user_name,password)

             VALUES('admin','');

COMMIT;

2.从SQL文件中导入数据到MYSQL中：

1>首先，我们应该在cmd中进入mysql指令界面中，格式很简单，就是 mysql -u[用户名] -h[主机所在地址，默认不写是localhost] -p 然后输入密码即可

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" 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2>直接使用 source [所在的路径//*.sql] 将SQL文件进行导入，接下来就会输出一大串的Query OK之类的信息了。

3、MYSQL中将数据库导出成SQL文件：

　　其实很简单的，就是一条语句就可以了，首先我们打开cmd，不用进mysql指令界面，直接按照下列格式将导出语句敲进去，然后再输入密码即可了：

　　mysqldump -h[主机所在IP] -u[用户名] -p [要导出的数据库]>[导出的路径//[文件名].sql]

好吧，直接这样看可能有点抽象，我们来举个例子，目前我的MYSQL中有一个数据库bookinfodb，现在我要将它导出并且保存到D盘中。

这个时候我们再到D盘目录下，我们就可以看到多了一个test.sql文件了

三、Mysql获取表中最后一行记录的语句？

排序后取得第一条记录

SELECT * FROM tb ORDER BY id DESC LIMIT 1

【注】在JDBC中有可以在执行时，取得插入时产生的主键：

 //方法一：

 long key =-1L;

 Statement statement = connection.createStatement();

 statement.executeUpdate(YOUR_SQL_HERE,Statement.RETURN_GENERATED_KEYS);

 ResultSet rs = statement.getGeneratedKeys();

 if(rs !=null&& rs.next()){

 key = rs.getLong(1);

 }

 //方法二：

 PreparedStatement ps = con.prepareStatement(sql,Statement.RETURN_GENERATED_KEYS);

 statement.executeUpdate();

 ResultSet rs = statement.getGeneratedKeys();

 //方法三：下面这种可精确取得某个字段

 PreparedStatement ps = con.prepareStatement(sql, new String[]{"USER_ID"})

四、MySQL级联删除和更新

首先，目前在产品环境可用的MySQL版本（指4.0.x和4.1.x）中，只有InnoDB引擎才允许使用外键，所以，我们的数据表必须使用InnoDB引擎。

下面，我们先创建以下测试用数据库表：

CREATE TABLE `roottb` (

  `id` INT(11) UNSIGNED AUTO_INCREMENT NOT NULL,

  `data` VARCHAR(100) NOT NULL DEFAULT '',

  PRIMARY KEY (`id`)

) TYPE=InnoDB;

CREATE TABLE `subtb` (

  `id` INT(11) UNSIGNED AUTO_INCREMENT NOT NULL,

  `rootid` INT(11) UNSIGNED NOT NULL DEFAULT '',

  `data` VARCHAR(100) NOT NULL DEFAULT '',

  PRIMARY KEY (`id`),

  INDEX (`rootid`),

  FOREIGN KEY (`rootid`) REFERENCES roottb(`id`) ON DELETE CASCADE

) TYPE=InnoDB;

注意：
1、必须使用InnoDB引擎；
2、外键必须建立索引（INDEX）；
3、外键绑定关系这里使用了“ ON DELETE CASCADE”，意思是如果外键对应数据被删除，将关联数据完全删除，更多信息请参考MySQL手册中关于InnoDB的文档；

五、mysql update语句问题：You can't specify target table 'user' for update in FROM clause

原因是mysql不支持从选择的表再去修改，所以构造个临时表来解决问题

Error Code: 1093. You can't specify target table 'ws_product' for update in FROM clause

这个是我们在使用update或者delete语句时，在where条件里面加入的子查询导致的。例如如下的update语句：

update product set type = 'static' where id in (
select id from product where first_name ='superman'
);

修改上述语句为下面这样，该问题可以解决：

update ws_product set type = 'static' where id in (
select id form (
select id from ws_product where first_name ='superman'
) xx
);

注意，这样一定要给最里面的子查询定义一个别名，不然会报另外一个错误：

Error Code: 1248. Every derived table must have its own alias