mysql連接查詢

實驗中涉及到兩個表的結構：

mysql> show create table lee;
+-------+------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                   |
+-------+------------------------------------------------------------------------+
| lee   | CREATE TABLE `lee` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(5) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=1200 DEFAULT CHARSET=latin1 |
+-------+------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> show create table lee1;
+-------+------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                  |
+-------+------------------------------------------------------------------------+
| lee1  | CREATE TABLE `lee1` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `gameid` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=201 DEFAULT CHARSET=latin1 |
+-------+------------------------------------------------------------------------+
1 row in set (0.00 sec)

一、連接查詢類型：

1、內連接查詢：

select lee.id , lee1.gameid from lee inner join lee1 using(id) where lee.id = 100; 或者
select lee.id, lee1.gameid  from lee inner join lee1 on lee.id=lee1.id where lee.id = 100;
+-----+---------+
| id  | gameid  |
+-----+---------+
| 100 | 1000100 |
+-----+---------+

2、左（右）外連接查詢：

mysql> select * from lee left join lee1 on lee.id = lee1.id where lee.id = 1197;
+------+-------+------+--------+
| id   | name  | id   | gameid |
+------+-------+------+--------+
| 1197 | lee11 | NULL |   NULL |
+------+-------+------+--------+
1 row in set (0.00 sec)

右外連接與上述類似，此處略過

二、左外連接、右外連接、內連接區別：

lee lee1 表初始內容

mysql> select * from lee join lee1 on lee.id = lee1.id limit 10;
+----+-------+------+--------+
| id | name  | id   | gameid |
+----+-------+------+--------+
|  1 | lee1  |    1 |  10001 |
|  2 | lee2  |    2 |  10002 |
|  3 | lee3  |    3 |  10003 |
|  4 | lee4  |    4 |  10004 |
|  5 | lee5  |    5 |  10005 |
|  6 | lee6  |    6 |  10006 |
|  7 | lee7  |    7 |  10007 |
|  8 | lee8  |    8 |  10008 |
|  9 | lee9  |    9 |  10009 |
| 10 | lee10 |   10 | 100010 |
+----+-------+------+--------+
10 rows in set (0.00 sec)

分別刪除兩個表各一條記錄

mysql> delete from lee1 where id = 6;
Query OK, 1 row affected (0.00 sec)
mysql> delete from lee where id = 7;
Query OK, 1 row affected (0.00 sec)

mysql> select * from lee left join lee1 on lee.id = lee1.id limit 10;
+----+-------+------+--------+
| id | name  | id   | gameid |
+----+-------+------+--------+
|  1 | lee1  |    1 |  10001 |
|  2 | lee2  |    2 |  10002 |
|  3 | lee3  |    3 |  10003 |
|  4 | lee4  |    4 |  10004 |
|  5 | lee5  |    5 |  10005 |
|  6 | lee6  | NULL |   NULL |
|  8 | lee8  |    8 |  10008 |
|  9 | lee9  |    9 |  10009 |
| 10 | lee10 |   10 | 100010 |
| 11 | lee11 |   11 | 100011 |
+----+-------+------+--------+

說明：左外連接是join左側的表爲主，如果join右側的表不符合則用NULL填充

mysql> select * from lee right join lee1 on lee.id = lee1.id limit 10;
+------+-------+----+--------+
| id   | name  | id | gameid |
+------+-------+----+--------+
|    1 | lee1  |  1 |  10001 |
|    2 | lee2  |  2 |  10002 |
|    3 | lee3  |  3 |  10003 |
|    4 | lee4  |  4 |  10004 |
|    5 | lee5  |  5 |  10005 |
| NULL | NULL  |  7 |  10007 |
|    8 | lee8  |  8 |  10008 |
|    9 | lee9  |  9 |  10009 |
|   10 | lee10 | 10 | 100010 |
|   11 | lee11 | 11 | 100011 |
+------+-------+----+--------+
10 rows in set (0.00 sec)

說明：同理，右外連接是以join右側的表爲主，如果join左側的表不符合則用NULL填充

mysql> select * from lee inner join lee1 on lee.id = lee1.id limit 10;
+----+-------+----+--------+
| id | name  | id | gameid |
+----+-------+----+--------+
|  1 | lee1  |  1 |  10001 |
|  2 | lee2  |  2 |  10002 |
|  3 | lee3  |  3 |  10003 |
|  4 | lee4  |  4 |  10004 |
|  5 | lee5  |  5 |  10005 |
|  8 | lee8  |  8 |  10008 |
|  9 | lee9  |  9 |  10009 |
| 10 | lee10 | 10 | 100010 |
| 11 | lee11 | 11 | 100011 |
| 12 | lee12 | 12 | 100012 |
+----+-------+----+--------+
10 rows in set (0.00 sec)

說明：可以看出inner連接是取左右外連接的並集