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
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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 |
| himi3 | h | beijing | m | 1989-9-23 | null |
| inserthimi | h | anhui | m | 1989-9-23 | null |
| tommy | m | chaoxian | w | 19890823 | 2100-10-10 |
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
| tommy | m | chaoxian | w | 1990-1-1 | 2100-10-10 |
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 |
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 |
| 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 |
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';
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';
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');
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 |
| himi3 | 1989-9-23 |
| inserthimi | 1989-9-23 |
| tommy | 1990-1-1 |
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 |
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 |
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 |
| 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;
| xiao |
| chinle |
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 |
| 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 |
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 |
| 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 |
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 |
| 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 |
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