更多的知识 见
1、使用SHOW语句找出在服务器上当前存在什么数据库:
mysql> SHOW DATABASES; +----------+ | Database | +----------+ | mysql | | test | +----------+ 3 rows in set (0.00 sec) |
mysql> CREATE TABLE mytable (name VARCHAR(20), sex CHAR(1), -> birth DATE, birthaddr VARCHAR(20)); Query OK, 0 rows affected (0.00 sec) |
mysql> SHOW TABLES; +---------------------+ | Tables in menagerie | +---------------------+ | mytables | +---------------------+ |
mysql> DESCRIBE mytable; +-------------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------------+-------------+------+-----+---------+-------+ | name | varchar(20) | YES | | NULL | | | sex | char(1) | YES | | NULL | | | birth | date | YES | | NULL | | | deathaddr | varchar(20) | YES | | NULL | | +-------------+-------------+------+-----+---------+-------+ 4 rows in set (0.00 sec) |
mysql> insert into mytable -> values (′abccs′,′f′,′1977-07-07′,′china′); Query OK, 1 row affected (0.05 sec) |
abccs f 1977-07-07 china mary f 1978-12-12 usa tom m 1970-09-02 usa |
8:删除数据库和数据表
删除数据库 drop database db_name;
删除数据表 drop table table_name;
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1、从数据库表中检索信息
实际上,前面我们已经用到了SELECT语句,它用来从数据库表中检索信息。 select语句格式一般为: SELECT 检索关键词 FROM 被检索的表 WHERE 检索条件(可选) 以前所使用的“ * ”表示选择所有的列。下面继续使用我们在上篇文章中创建的表mytable。 2、查询所有数据: 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 | +----------+------+------------+----------+ 3 row in set (0.00 sec) |
上面修改了tom的出生日期,我们可以选择tom这一行来看看是否已经有了变化:
mysql> select * from mytable where name = "tom"; +--------+------+------------+------------+ | name |sex | birth | birthaddr | +--------+------+------------+------------+ | tom |m | 1973-09-02 | usa | +--------+------+------------+------------+ 1 row in set (0.06 sec) |
mysql> SELECT * FROM mytable WHERE sex = "f" AND birthaddr = "china"; +--------+------+------------+------------+ | name |sex | birth | birthaddr | +--------+------+------------+------------+ | abccs |f | 1977-07-07 | china | +--------+------+------------+------------+ 1 row in set (0.06 sec) |
mysql> SELECT name FROM mytable; +----------+ | name | +----------+ | abccs | | mary | | tom | +----------+ 3 row in set (0.00 sec) |
mysql> SELECT name, birth FROM mytable ORDER BY birth; +----------+------------+ | name | birth | +----------+------------+ | tom | 1973-09-02 | | abccs | 1977-07-07 | | mary | 1978-12-12 | +----------+------------+ 3 row in set (0.00 sec) |
mysql> SELECT name, birth FROM mytable ORDER BY birth DESC; +----------+------------+ | name | birth | +----------+------------+ | mary | 1978-12-12 | | abccs | 1977-07-07 | | tom | 1973-09-02 | +----------+------------+ 3 row in set (0.00 sec) |
mysql> SELECT COUNT(*) FROM mytable; +----------+ | COUNT(*) | +----------+ | 3 | +----------+ 1 row in set (0.06 sec) 员工中男女数量: mysql> SELECT sex, COUNT(*) FROM mytable GROUP BY sex; +------+----------+ | sex | COUNT(*) | +------+----------+ | f | 2 | | m | 1 | +------+----------+ 2 row in set (0.00 sec) |