【MySQL数据库开发之三】MySQL 获得数据库和表操作！

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通过上一篇的介绍，大家可以创建自己的数据库和表以及插入表中数据等等，本章继续介绍更多的数据库的相关操作；

  1.  查看所有表单数据：（这里我直接使用上一篇创建的himiDB数据库与其中的people表进行讲解，还不太熟悉的请移步到上一篇的博文）   步骤：（获取）显示所有已存在的数据库->使用himidb数据库->（获取）显示所有表->（获取）显示所有表内的数据

 

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| himiDB             |
| mysql              |
| performance_schema |
| test               |
+--------------------+
5 rows in set (0.00 sec)

mysql> use himidb;
Database changed
mysql> show tables;
+------------------+
| Tables_in_himidb |
+------------------+
| people           |
+------------------+
1 row in set (0.00 sec)

mysql> select *from people;
+------------+------+----------+------+-----------+------------+
| name       | mz   | city     | sex  | birthday  | deathday   |
+------------+------+----------+------+-----------+------------+
| himi       | h    | beijing  | m    | 1989-9-23 | NULL       |
| himi       | h    | beijing  | m    | 1989-9-23 | NULL       |
| himi3      | h    | beijing  | m    | 1989-9-23 | NULL       |
| insertHimi | h    | Anhui    | m    | 1989-9-23 | NULL       |
| tommy      | m    | chaoxian | w    | 19890823  | 2100-10-10 |
+------------+------+----------+------+-----------+------------+
5 rows in set (0.00 sec)

2. 假设我们修改people中的tommy 的生日为  1990-1-1日：

2.1：第一种方式可以通过txt进行，假设我们已经有一个txt存储了所有表内数据，并且tommy的生日在txt中已经是最新的了，那么我们就可以直接如下来进行更改（注意这种方式是删除以前所有表元素直接进行重新添加的操作！如果你没有之前这些数据就不要使用此方式）

 

mysql> DELETE FROM people;
mysql> LOAD DATA LOCAL INFILE '/xxx/xxx/people.txt' INTO TABLE people;

2.2：使用UPDATE进行指向性修改；

语句形式： update xx(表名) set xx(item名)   =’xxx新value’ where xx(item索引) =”where中item索引的对应value”;

示例：

 

mysql> update people set birthday = '1990-1-1' where name = 'tommy';
Query OK, 1 row affected (0.11 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select *from people;
+------------+------+----------+------+-----------+------------+
| name       | mz   | city     | sex  | birthday  | deathday   |
+------------+------+----------+------+-----------+------------+
| himi       | h    | beijing  | m    | 1989-9-23 | NULL       |
| himi       | h    | beijing  | m    | 1989-9-23 | NULL       |
| himi3      | h    | beijing  | m    | 1989-9-23 | NULL       |
| insertHimi | h    | Anhui    | m    | 1989-9-23 | NULL       |
| tommy      | m    | chaoxian | w    | 1990-1-1  | 2100-10-10 |
+------------+------+----------+------+-----------+------------+
5 rows in set (0.00 sec)

3.查看特定条件所有数据：

 

mysql> select *from people where name='himi';
+------+------+---------+------+-----------+----------+
| name | mz   | city    | sex  | birthday  | deathday |
+------+------+---------+------+-----------+----------+
| himi | h    | beijing | m    | 1989-9-23 | NULL     |
| himi | h    | beijing | m    | 1989-9-23 | NULL     |
+------+------+---------+------+-----------+----------+
2 rows in set (0.08 sec)

通过以上可以看出是在 select *from xx 后加入指向，比较容易理解；

 继续查看哪些是大于1990年之前的额people：

 

mysql> select *from people where birthday <'1990-1-1';
+------------+------+---------+------+-----------+----------+
| name       | mz   | city    | sex  | birthday  | deathday |
+------------+------+---------+------+-----------+----------+
| himi       | h    | beijing | m    | 1989-9-23 | NULL     |
| himi       | h    | beijing | m    | 1989-9-23 | NULL     |
| himi3      | h    | beijing | m    | 1989-9-23 | NULL     |
| insertHimi | h    | Anhui   | m    | 1989-9-23 | NULL     |
+------------+------+---------+------+-----------+----------+
4 rows in set (0.01 sec)

继续查看表中有几个woman：

 

mysql> select *from people where sex ="w";
+-------+------+----------+------+----------+------------+
| name  | mz   | city     | sex  | birthday | deathday   |
+-------+------+----------+------+----------+------------+
| tommy | m    | chaoxian | w    | 1990-1-1 | 2100-10-10 |
+-------+------+----------+------+----------+------------+
1 row in set (0.00 sec)

继续查看表中既是woman又是在1990年以前的：（AND）

 

mysql> select *from people where sex ="m" and birthday < '1990-1-1';
+------------+------+---------+------+-----------+----------+
| name       | mz   | city    | sex  | birthday  | deathday |
+------------+------+---------+------+-----------+----------+
| himi       | h    | beijing | m    | 1989-9-23 | NULL     |
| himi       | h    | beijing | m    | 1989-9-23 | NULL     |
| himi3      | h    | beijing | m    | 1989-9-23 | NULL     |
| insertHimi | h    | Anhui   | m    | 1989-9-23 | NULL     |
+------------+------+---------+------+-----------+----------+
4 rows in set (0.00 sec)

继续查看表中叫tommy 或者 是beijing地区的：(OR)

 

mysql> select *from people where city='beijing' or birthday <'1990-1-1';
+------------+------+---------+------+-----------+----------+
| name       | mz   | city    | sex  | birthday  | deathday |
+------------+------+---------+------+-----------+----------+
| himi       | h    | beijing | m    | 1989-9-23 | NULL     |
| himi       | h    | beijing | m    | 1989-9-23 | NULL     |
| himi3      | h    | beijing | m    | 1989-9-23 | NULL     |
| insertHimi | h    | Anhui   | m    | 1989-9-23 | NULL     |
+------------+------+---------+------+-----------+----------+
4 rows in set (0.00 sec)

AND和OR可以混用，但AND比OR具有更高的优先级。如果使用两个操作符，使用圆括号进行分组~如下：

 

mysql> select *from people where (city='beijing' and sex='w') or (city ='chaoxian' and sex = 'w');
+-------+------+----------+------+----------+------------+
| name  | mz   | city     | sex  | birthday | deathday   |
+-------+------+----------+------+----------+------------+
| tommy | m    | chaoxian | w    | 1990-1-1 | 2100-10-10 |
+-------+------+----------+------+----------+------------+
1 row in set (0.00 sec)

4.查看所有数据的特定条件：

假如我们需要查看所有人的性别 和名字：

 

mysql> select name,birthday from people;
+------------+-----------+
| name       | birthday  |
+------------+-----------+
| himi       | 1989-9-23 |
| himi       | 1989-9-23 |
| himi3      | 1989-9-23 |
| insertHimi | 1989-9-23 |
| tommy      | 1990-1-1  |
+------------+-----------+
5 rows in set (0.00 sec)

从上面的名字来看，发现了重复的名字，那么如果只想让同一名字只显示一个，可以使用 distinct 关键字；如下：

 

mysql> select distinct name from people;
+------------+
| name       |
+------------+
| himi       |
| himi3      |
| insertHimi |
| tommy      |
+------------+
4 rows in set (0.00 sec)

来个复杂点的：使用一个WHERE子句结合行选择与列选择

 

mysql> select name from people where city='chaoxian' and birthday = '1990-1-1';+-------+
| name  |
+-------+
| tommy |
+-------+
1 row in set (0.00 sec)

选择出的列根据生日进行排序显示(提前Himi这里又往表中添加了很多人)

 

mysql> select birthday from people order by birthday;
+-----------+
| birthday  |
+-----------+
| 1989-9-23 |
| 1989-9-23 |
| 1989-9-23 |
| 1989-9-23 |
| 1990-1-1  |
| 1991-2-3  |
| 1992-5-3  |
+-----------+
7 rows in set (0.00 sec)

选择出的列根据名字降序进行排序显示：

 

mysql> select name from people order by name desc;
+------------+
| name       |
+------------+
| xiao       |
| tommy      |
| insertHimi |
| himi3      |
| himi       |
| himi       |
| chinle     |
+------------+
7 rows in set (0.00 sec)

5. 日起计算；

MySQL提供了几个函数，可以用来计算日期，例如，计算年龄或提取日期部分:

YEAR()提取日期的年部分，

RIGHT(x,y)提取 x 日期的MM-DD (日历年)  部分的最右面y个字符。

 

mysql> select name ,birthday,curdate(),(year(curdate())-year(birthday))- (right(curdate(),5)<right(birthday,5)) from people;
+------------+-----------+------------+--------------------------------------------------------------------------+
| name       | birthday  | curdate()  | (year(curdate())-year(birthday))- (right(curdate(),5)<right(birthday,5)) |
+------------+-----------+------------+--------------------------------------------------------------------------+
| himi       | 1989-9-23 | 2012-04-17 |                                                                       23 |
| himi       | 1989-9-23 | 2012-04-17 |                                                                       23 |
| himi3      | 1989-9-23 | 2012-04-17 |                                                                       23 |
| insertHimi | 1989-9-23 | 2012-04-17 |                                                                       23 |
| tommy      | 1990-1-1  | 2012-04-17 |                                                                       22 |
| xiao       | 1991-2-3  | 2012-04-17 |                                                                       20 |
| chinle     | 1992-5-3  | 2012-04-17 |                                                                       19 |
+------------+-----------+------------+--------------------------------------------------------------------------+
7 rows in set (0.00 sec)

下面我们算下死亡时间和当前时间的差值，其中我们排除deathday为NULL的人。

 

mysql> select name ,deathday,curdate(),(year(curdate())-year(deathday))- (right(curdate(),5)<right(deathday,5)) from people where deathday is not null;
+--------+------------+------------+--------------------------------------------------------------------------+
| name   | deathday   | curdate()  | (year(curdate())-year(deathday))- (right(curdate(),5)<right(deathday,5)) |
+--------+------------+------------+--------------------------------------------------------------------------+
| tommy  | 2100-10-10 | 2012-04-17 |                                                                      -89 |
| xiao   | 1994-1-1   | 2012-04-17 |                                                                       17 |
| chinle | 1994-1-1   | 2012-04-17 |                                                                       17 |
+--------+------------+------------+--------------------------------------------------------------------------+
3 rows in set (0.00 sec)

MySQL提供几个日期部分的提取函数，例如YEAR( )、MONTH( )和DAYOFMONTH( )。在这里MONTH()是适合的函数。为了看它怎样工作，运行一个简单的查询: 

 

mysql> select name ,birthday, year(birthday),month(birthday) ,dayofmonth(birthday) from people;
+------------+-----------+----------------+-----------------+----------------------+
| name       | birthday  | year(birthday) | month(birthday) | dayofmonth(birthday) |
+------------+-----------+----------------+-----------------+----------------------+
| himi       | 1989-9-23 |           1989 |               9 |                   23 |
| himi       | 1989-9-23 |           1989 |               9 |                   23 |
| himi3      | 1989-9-23 |           1989 |               9 |                   23 |
| insertHimi | 1989-9-23 |           1989 |               9 |                   23 |
| tommy      | 1990-1-1  |           1990 |               1 |                    1 |
| xiao       | 1991-2-3  |           1991 |               2 |                    3 |
| chinle     | 1992-5-3  |           1992 |               5 |                    3 |
+------------+-----------+----------------+-----------------+----------------------+
7 rows in set (0.00 sec)

练习：找到一个下个月是几月份：

 

mysql> select name,birthday,month(birthday)+1 from people;
+------------+-----------+-------------------+
| name       | birthday  | month(birthday)+1 |
+------------+-----------+-------------------+
| himi       | 1989-9-23 |                10 |
| himi       | 1989-9-23 |                10 |
| himi3      | 1989-9-23 |                10 |
| insertHimi | 1989-9-23 |                10 |
| tommy      | 1990-1-1  |                 2 |
| xiao       | 1991-2-3  |                 3 |
| chinle     | 1992-5-3  |                 6 |
+------------+-----------+-------------------+
7 rows in set (0.00 sec)