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HomeDatabaseMysql Tutorial学习MySQL多表操作和备份处理_MySQL

学习MySQL多表操作和备份处理_MySQL

Jun 01, 2016 pm 02:12 PM
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  多表操作
  在一个数据库中,可能存在多个表,这些表都是相互关联的。我们继续使用前面的例子。前面建立的表中包含了员工的一些基本信息,如姓名、性别、出生日期、出生地。我们再创建一个表,该表用于描述员工所发表的文章,内容包括作者姓名、文章标题、发表日期。
  
  1、查看第一个表mytable的内容:
  
  mysql> select * from mytable;
  +----------+------+------------+-----------+
  | name | sex | birth | birthaddr |
  +----------+------+------------+-----------+
  | abccs |f | 1977-07-07 | china |
  | mary |f | 1978-12-12 | usa |
  | tom |m | 1970-09-02 | usa |
  +----------+------+------------+-----------+
  
  2、创建第二个表title(包括作者、文章标题、发表日期):
  
  mysql> create table title(writer varchar(20) not null,
  -> title varchar(40) not null,
  -> senddate date);
      向该表中填加记录,最后表的内容如下:
  
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<ccid_code> mysql> select * from title;<br>  +--------+-------+------------+<br>  | writer | title | senddate |<br>  +--------+-------+------------+<br>  | abccs | a1 | 2000-01-23 |<br>  | mary | b1 | 1998-03-21 |<br>  | abccs | a2 | 2000-12-04 |<br>  | tom | c1 | 1992-05-16 |<br>  | tom | c2 | 1999-12-12 |<br>  +--------+-------+------------+<br>  5 rows in set (0.00sec)<br>  <br>  <b>3、多表查询</b><br>  现在我们有了两个表: mytable 和 title。利用这两个表我们可以进行组合查询:<br>  例如我们要查询作者abccs的姓名、性别、文章:<br>  <br>  mysql> SELECT name,sex,title FROM mytable,title<br>  -> WHERE name=writer AND name=′abccs′;<br>  +-------+------+-------+<br>  | name | sex | title |<br>  +-------+------+-------+<br>  | abccs | f | a1 |<br>  | abccs | f | a2 |<br>  +-------+------+-------+<br>  <br>  上面例子中,由于作者姓名、性别、文章记录在两个不同表内,因此必须使用组合来进行查询。必须要指定一个表中的记录如何与其它表中的记录进行匹配。<br>  <br>  注意:如果第二个表title中的writer列也取名为name(与mytable表中的name列相同)而不是writer时,就必须用mytable.name和title.name表示,以示区别。<br>  <br>  再举一个例子,用于查询文章a2的作者、出生地和出生日期:<br>  <br>  mysql> select title,writer,birthaddr,birth from mytable,title<br>  -> where mytable.name=title.writer and title=′a2′;<br>  +-------+--------+-----------+------------+<br>  | title | writer | birthaddr | birth |<br>  +-------+--------+-----------+------------+<br>  | a2 | abccs | china | 1977-07-07 |<br>  +-------+--------+-----------+------------+<br>  <br>  <b>修改和备份、批处理</b><br>  有时我们要对数据库表和数据库进行修改和删除,可以用如下方法实现:<br>  <br>  1、增加一列:<br>  如在前面例子中的mytable表中增加一列表示是否单身single:<br>  mysql> alter table mytable add column single char(1);<br>  <br>  2、修改记录<br>  将abccs的single记录修改为“y”:<br>  mysql> update mytable set single=′y′ where name=′abccs′;   现在来看看发生了什么:<br>  <br>  mysql> select * from mytable;<br>  +----------+------+------------+-----------+--------+<br>  | name | sex | birth | birthaddr | single |<br>  +----------+------+------------+-----------+--------+<br>  | abccs |f | 1977-07-07 | china | y |<br>  | mary |f | 1978-12-12 | usa | NULL |<br>  | tom |m | 1970-09-02 | usa | NULL |<br>  +----------+------+------------+-----------+--------+<br>  <br>  3、增加记录<br>  前面已经讲过如何增加一条记录,为便于查看,重复与此:<br>  <br>  mysql> insert into mytable<br>  -> values (′abc′,′f′,′1966-08-17′,′china′,′n′);<br>  Query OK, 1 row affected (0.05 sec)<br>  <br>  查看一下:<br>  <br>  mysql> select * from mytable;<br>  +----------+------+------------+-----------+--------+<br>  | name | sex | birth | birthaddr | single |<br>  +----------+------+------------+-----------+--------+<br>  | abccs |f | 1977-07-07 | china | y |<br>  | mary |f | 1978-12-12 | usa | NULL |<br>  | tom |m | 1970-09-02 | usa | NULL |<br>  | abc |f | 1966-08-17 | china | n |<br>  +----------+------+------------+-----------+--------+<br>  <br>  4、删除记录<br>  用如下命令删除表中的一条记录:mysql> delete from mytable where name=′abc′;<br>  DELETE从表中删除满足由where给出的条件的一条记录。<br>  再显示一下结果:<br>  <br>  mysql> select * from mytable;<br>  +----------+------+------------+-----------+--------+<br>  | name | sex | birth | birthaddr | single |<br>  +----------+------+------------+-----------+--------+<br>  | abccs |f | 1977-07-07 | china | y |<br>  | mary |f | 1978-12-12 | usa | NULL |<br>  | tom |m | 1970-09-02 | usa | NULL |<br>  +----------+------+------------+-----------+--------+<br>  <br>  5、删除表:<br>  mysql> drop table ****(表1的名字),***表2的名字;<br>  可以删除一个或多个表,小心使用。<br>  <br>  6、数据库的删除:<br>  mysql> drop database 数据库名;<br>  小心使用。<br>  <br>  7、数据库的备份:<br>  退回到DOS:<br>  mysql> quit<br>  d:mysqlbin<br>  <br>  使用如下命令对数据库abccs进行备份:<br>  mysqldump --opt abccs>abccs.dbb<br>  abccs.dbb就是你的数据库abccs的备份文件。<br>  <br>  8、用批处理方式使用MySQL:<br>  <br>  首先建立一个批处理文件mytest.sql,内容如下:<br>  <br>  use abccs;<br>  select * from mytable;<br>  select name,sex from mytable where name=′abccs′;<br>  <br>  在DOS下运行如下命令:d:mysqlbin mysql   <br>  在屏幕上会显示执行结果。<br>  <br>  如果想看结果,而输出结果很多,则可以用这样的命令: mysql   <br>  我们还可以将结果输出到一个文件中: mysql  mytest.out
    </ccid_code>
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