mysql> SELECT name,sex,title FROM mytable,title -> WHERE name=writer AND name=′abccs′; +-------+------+-------+ | name | sex | title | +-------+------+-------+ | abccs | f | a1 | | abccs | f | a2 | +-------+------+-------+
mysql> select title,writer,birthaddr,birth from mytable,title -> where mytable.name=title.writer and title=′a2′; +-------+--------+-----------+------------+ | title | writer | birthaddr | birth | +-------+--------+-----------+------------+ | a2 | abccs | china | 1977-07-07 | +-------+--------+-----------+------------+
修改和备份、批处理 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：
1、增加一列： 如在前面例子中的mytable表中增加一列表示是否单身single: mysql> alter table mytable add column single char(1);
2、修改记录 将abccs的single记录修改为“y”： mysql> update mytable set single=′y′ where name=′abccs′; 现在来看看发生了什么：
mysql> select * from mytable; +----------+------+------------+-----------+--------+ | name | sex | birth | birthaddr | single | +----------+------+------------+-----------+--------+ | abccs |f | 1977-07-07 | china | y | | mary |f | 1978-12-12 | usa | NULL | | tom |m | 1970-09-02 | usa | NULL | +----------+------+------------+-----------+--------+
mysql> select * from mytable; +----------+------+------------+-----------+--------+ | name | sex | birth | birthaddr | single | +----------+------+------------+-----------+--------+ | abccs |f | 1977-07-07 | china | y | | mary |f | 1978-12-12 | usa | NULL | | tom |m | 1970-09-02 | usa | NULL | | abc |f | 1966-08-17 | china | n | +----------+------+------------+-----------+--------+
4、删除记录 用如下命令删除表中的一条记录：mysql> delete from mytable where name=′abc′; DELETE从表中删除满足由where给出的条件的一条记录。 再显示一下结果：
mysql> select * from mytable; +----------+------+------------+-----------+--------+ | name | sex | birth | birthaddr | single | +----------+------+------------+-----------+--------+ | abccs |f | 1977-07-07 | china | y | | mary |f | 1978-12-12 | usa | NULL | | tom |m | 1970-09-02 | usa | NULL | +----------+------+------------+-----------+--------+
5、删除表： mysql> drop table ****(表1的名字)，***表2的名字; 可以删除一个或多个表，小心使用。
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