2.5 修改数据
2.5.1 使用UPDATE语句来更新表中的数据
mysql> update emp set emp_id=100001 where emp_name='红枫';
修改结果显示如下：
+--------+----------+---------+---------+------------+---------+
| emp_id | emp_name | emp_age | emp_sal | emp_bir | emp_sex |
+--------+----------+---------+---------+------------+---------+
| 100005 | 啸天 | 27 | 3000 | 1979-07-10 | male |
| 100001 | 红枫 | 29 | 8000 | 1977-01-01 | male |
| 100002 | 丽鹃 | 27 | 7000 | 1979-12-31 | fmale |
+--------+----------+---------+---------+------------+---------+
3 rows in set (0.00 sec)
如果该语句没有后面的where限制，将会对表中所有的记录都进行修改。
如，给全部人加薪1000，可以如下修改：
mysql> update emp set emp_sal=emp_sal+1000;
修改结果显示如下：
+--------+----------+---------+---------+------------+---------+
| emp_id | emp_name | emp_age | emp_sal | emp_bir | emp_sex |
+--------+----------+---------+---------+------------+---------+
| 100005 | 啸天 | 27 | 4000 | 1979-07-10 | male |
| 100001 | 红枫 | 29 | 9000 | 1977-01-01 | male |
| 100002 | 丽鹃 | 27 | 8000 | 1979-12-31 | fmale |
+--------+----------+---------+---------+------------+---------+
3 rows in set (0.00 sec)
----------------------我------------割--------------------------
2.6 高级查询
2.6.1 记录查询
查询emp表中，emp_name为啸天的全部信息
mysql> select * from emp where emp_name='啸天';
查询结果显示如下：
+--------+----------+---------+---------+------------+---------+
| emp_id | emp_name | emp_age | emp_sal | emp_bir | emp_sex |
+--------+----------+---------+---------+------------+---------+
| 100005 | 啸天 | 27 | 4000 | 1979-07-10 | male |
+--------+----------+---------+---------+------------+---------+
1 row in set (0.00 sec)
查询emp表中，emp_sal，工资在5000以上的全部信息
mysql> select * from emp where emp_sal>5000;
查询结果显示如下：
+--------+----------+---------+---------+------------+---------+
| emp_id | emp_name | emp_age | emp_sal | emp_bir | emp_sex |
+--------+----------+---------+---------+------------+---------+
| 100001 | 红枫 | 29 | 9000 | 1977-01-01 | male |
| 100002 | 丽鹃 | 27 | 8000 | 1979-12-31 | fmale |
+--------+----------+---------+---------+------------+---------+
2 rows in set (0.00 sec)
查询emp表中在1978年1月1日之后出生的
mysql> select * from emp where emp_bir>'1978-01-01';
查询结果显示如下：
+--------+----------+---------+---------+------------+---------+
| emp_id | emp_name | emp_age | emp_sal | emp_bir | emp_sex |
+--------+----------+---------+---------+------------+---------+
| 100005 | 啸天 | 27 | 4000 | 1979-07-10 | male |
| 100002 | 丽鹃 | 27 | 8000 | 1979-12-31 | fmale |
+--------+----------+---------+---------+------------+---------+
2 rows in set (0.00 sec)
查询emp表中在1979年12月1日之前出生，工资在5000以上的
mysql> select * from emp where emp_bir<'1979-12-01' and emp_sal>5000;
查询结果显示如下：
+--------+----------+---------+---------+------------+---------+
| emp_id | emp_name | emp_age | emp_sal | emp_bir | emp_sex |
+--------+----------+---------+---------+------------+---------+
| 100001 | 红枫 | 29 | 9000 | 1977-01-01 | male |
+--------+----------+---------+---------+------------+---------+
1 row in set (0.00 sec)
2.6.2 字段查询
CEO查看工资情况
mysql> select emp_name,emp_sal from emp;
查询结果显示如下：
+----------+---------+
| emp_name | emp_sal |
+----------+---------+
| 啸天 | 4000 |
| 红枫 | 9000 |
| 丽鹃 | 8000 |
+----------+---------+
3 rows in set (0.00 sec)
查看1978年后出生的人的姓名、工资和性别
mysql> select emp_name,emp_sal,emp_sex from emp where emp_bir>"1977-12-31";
查询结果显示如下：
+----------+---------+---------+
| emp_name | emp_sal | emp_sex |
+----------+---------+---------+
| 啸天 | 4000 | male |
| 丽鹃 | 8000 | fmale |
+----------+---------+---------+
2 rows in set (0.00 sec)
2.6.3 查询结果排序
用ORDER BY语句对emp表中所有员工工资高低顺序查询结果（默认是从低到高——升序）
mysql> select * from emp order by emp_sal;
查询结果显示如下：
+--------+----------+---------+---------+------------+---------+
| emp_id | emp_name | emp_age | emp_sal | emp_bir | emp_sex |
+--------+----------+---------+---------+------------+---------+
| 100005 | 啸天 | 27 | 4000 | 1979-07-10 | male |
| 100002 | 丽鹃 | 27 | 8000 | 1979-12-31 | fmale |
| 100001 | 红枫 | 29 | 9000 | 1977-01-01 | male |
+--------+----------+---------+---------+------------+---------+
3 rows in set (0.00 sec)
用DESC关键字来进行从高到低排序——降序
mysql> select * from emp order by emp_sal desc;
查询结果显示如下：
+--------+----------+---------+---------+------------+---------+
| emp_id | emp_name | emp_age | emp_sal | emp_bir | emp_sex |
+--------+----------+---------+---------+------------+---------+
| 100001 | 红枫 | 29 | 9000 | 1977-01-01 | male |
| 100002 | 丽鹃 | 27 | 8000 | 1979-12-31 | fmale |
| 100005 | 啸天 | 27 | 4000 | 1979-07-10 | male |
+--------+----------+---------+---------+------------+---------+
3 rows in set (0.00 sec)
2.6.4 查询结果数量的限制
用LIMIT查看emp表中工资收入排名前两个员工的资料：
mysql> select * from emp order by emp_sal desc limit 2;
查询结果显示如下：
+--------+----------+---------+---------+------------+---------+
| emp_id | emp_name | emp_age | emp_sal | emp_bir | emp_sex |
+--------+----------+---------+---------+------------+---------+
| 100001 | 红枫 | 29 | 9000 | 1977-01-01 | male |
| 100002 | 丽鹃 | 27 | 8000 | 1979-12-31 | fmale |
+--------+----------+---------+---------+------------+---------+
2 rows in set (0.00 sec)
查看工资排名第2到第3的员工资料：
mysql> select * from emp order by emp_sal desc limit 1,2;
查询结果显示如下：
+--------+----------+---------+---------+------------+---------+
| emp_id | emp_name | emp_age | emp_sal | emp_bir | emp_sex |
+--------+----------+---------+---------+------------+---------+
| 100002 | 丽鹃 | 27 | 8000 | 1979-12-31 | fmale |
| 100005 | 啸天 | 27 | 4000 | 1979-07-10 | male |
+--------+----------+---------+---------+------------+---------+
2 rows in set (0.01 sec)
使用rand()抽样调查，随机抽取2个员工，查看其资料
mysql> select * from emp order by rand() limit 2;
如如下结果：（随机的）
+--------+----------+---------+---------+------------+---------+
| emp_id | emp_name | emp_age | emp_sal | emp_bir | emp_sex |
+--------+----------+---------+---------+------------+---------+
| 100005 | 啸天 | 27 | 4000 | 1979-07-10 | male |
| 100001 | 红枫 | 29 | 9000 | 1977-01-01 | male |
+--------+----------+---------+---------+------------+---------+
2 rows in set (0.01 sec)
2.6.5 查询结果的字段联合和重新命名
mysql> select concat(emp_id," ",emp_name) from emp;
查询结果：
+------------------------------+
| concat(emp_id," ",emp_name) |
+------------------------------+
| 100005 啸天 |
| 100001 红枫 |
| 100002 丽鹃 |
+------------------------------+
3 rows in set (0.00 sec)
