本文共 911 字，大约阅读时间需要 3 分钟。
准备(两张表t1,t2)：
表t1:
mysql> select * from t1;
+-------+---------+
| t1_id | t1_name |
+-------+---------+
| 1 | t1_1 |
| 2 | t1_2 |
+-------+---------+
2 rows in set (0.02 sec)
表t2:
mysql> select * from t2;
+-------+---------+
| t2_id | t2_name |
+-------+---------+
| 2 | t2_2 |
| 3 | t2_3 |
+-------+---------+
2 rows in set (0.03 sec)
并集实例：
mysql> select t1.t1_id,t2.t2_id,t1.t1_name from t1 left join t2 on t1.t1_id=t2.t2_id;
+-------+-------+---------+
| t1_id | t2_id | t1_name |
+-------+-------+---------+
| 1 | NULL | t1_1 |
| 2 | 2 | t1_2 |
+-------+-------+---------+
2 rows in set (0.02 sec)
交集实例：
mysql> select t1.t1_id,t2.t2_id,t1.t1_name from t1,t2 where t1.t1_id=t2.t2_id;
+-------+-------+---------+
| t1_id | t2_id | t1_name |
+-------+-------+---------+
| 2 | 2 | t1_2 |
+-------+-------+---------+
1 row in set (0.01 sec)
本文转自 Lee_吉 博客，原文链接： http://blog.51cto.com/12173069/1968871 如需转载请自行联系原作者
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