例如：
原表country
mysql> select * from country;
+----+----------+------------+------+----------+
| id | name | population | area | language |
+----+----------+------------+------+----------+
| 1 | mysql | 13 | 960 | chinese |
| 2 | american | 4 |60 | english |
| 3 | japan | 89 | 30 | jpanese |
| 4 | england | 2 | 300 | english |
+----+----------+------------+------+----------
原表library
mysql> select * from library;
+----+---------------+--------+-------+
| id | name | author | price |
+----+---------------+--------+-------+
| 1 | java范例大全 | 张帆 | 99 |
| 2 | mysql | 潘凯华 | 50 |
| 3 | sqlserver2005 | 刘智勇 | 80 |
| 4 | mysql | 李慧 | 50 |
+----+---------------+--------+-------+
mysql> select area,author from country,library where country.name=library.name;
+------+--------+
| area | author |
+------+--------+
| 960 | 潘凯华 |
| 960 | 李慧 |
+------+--------+
2 左外连接mysql> select language,area,author from country left join library on country.name=library.name; //返回的结果除内连接的数据外，还包括左表中不符合条件数据
+----------+------+--------+
| language | area | author |
+----------+------+--------+
| chinese | 960 | 潘凯华 |
| chinese | 960 | 李慧 |
| english | 60 | null |
| jpanese | 30 | null |
| english | 300 | null |
+----------+------+--------+
3 右外连接
mysql> select language,area,author from country right joinlibrary on country.name=library.name; // //返回的结果除内连接的数据外，还包括右表中不符合条件数据
+----------+------+--------+
| language | area | author |
+----------+------+--------+
| null | null | 张帆 |
| chinese | 960 | 潘凯华 |
| null | null | 刘智勇 |
| chinese | 960 | 李慧 |
+----------+------+--------+
4 复合条件连接查询
mysql>select population,area,author,price from country,library where country.name=library.name and price>30;
5 子查询
1 带in关键字的子查询 mysql> select * from country wherename in(select name from library);