and Yan 18 study php-27th Day-about the difference between the inner connection

With Yan 18 study php-27th Day-the difference between the right and left inner joins
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Mysql> CREATE TABLE Boy (
Bname varchar (20),
Other char (1)
) engine MyISAM charset UTF8;
Query OK, 0 rows affected (0.23 sec)


Mysql>
mysql> INSERT INTO Boy
Values
(' Dick Silk ', ' A '),
(' John Doe ', ' B '),
(' Harry ', ' C '),
(' Gao Fu Shuai ', ' D '),
(' Zheng Qi ', ' E ');
Query OK, 5 rows Affected (0.02 sec)
Records:5 duplicates:0 warnings:0


Mysql>
Mysql>
Mysql>
Mysql> CREATE TABLE Girl (
Gname varchar (20),
Other char (1)
) engine MyISAM charset UTF8;
Query OK, 0 rows affected (0.16 sec)


Mysql>
mysql> INSERT INTO Girl
Values
(' Stewardess ', ' B '),
(' Big s ', ' C '),
(' Gillian ', ' D '),
(' Cecilia Cheung ', ' D '),
(' Lin Daiyu ', ' E '),
(' Bao Chai ', ' F ');
Query OK, 6 rows affected (0.03 sec)
Records:6 duplicates:0 warnings:0


Mysql> select * from Boy;
+--------+-------+
| bname | Other |
+--------+-------+
| Cock Wire | A |
| John Doe | B |
| Harry | C |
| Ko Fu Handsome | D |
| Zheng Qi | E |
+--------+-------+
5 rows in Set (0.00 sec)


Mysql> select * from girl;
+--------+-------+
| Gname | Other |
+--------+-------+
| Stewardess | B |
| Big S | C |
| Gillian | D |
| Cecilia Cheung | D |
| Lin Daiyu | E |
| Bao Chai | F |
+--------+-------+
6 rows in Set (0.00 sec)


Mysql> Select boy.*,girl.* from
Boy left joins girl on Boy.other=girl.other;
+--------+-------+--------+-------+
| bname | Other | Gname | Other |
+--------+-------+--------+-------+
| Cock Wire | A | NULL | NULL |
| John Doe | B | Stewardess | B |
| Harry | C | Big S | C |
| Ko Fu Handsome | D | Gillian | D |
| Ko Fu Handsome | D | Cecilia Cheung | D |
| Zheng Qi | E | Lin Daiyu | E |
+--------+-------+--------+-------+
6 rows in Set (0.00 sec)


Mysql> #女生上台, with the other half, without the other half, with null
Mysql> Select boy.*,girl.* from
-Girl left Join boy on Boy.other=girl.other;
+--------+-------+--------+-------+
| bname | Other | Gname | Other |
+--------+-------+--------+-------+
| John Doe | B | Stewardess | B |
| Harry | C | Big S | C |
| Ko Fu Handsome | D | Gillian | D |
| Ko Fu Handsome | D | Cecilia Cheung | D |
| Zheng Qi | E | Lin Daiyu | E |
| NULL | NULL | Bao Chai | F |
+--------+-------+--------+-------+
6 rows in Set (0.00 sec)


Mysql> #注意, a LEFT join B, is not to say that a table must be on the right, just say in the query data, a table is the subject
Mysql> select * from Boy;
+--------+-------+
| bname | Other |
+--------+-------+
| Cock Wire | A |
| John Doe | B |
| Harry | C |
| Ko Fu Handsome | D |
| Zheng Qi | E |
+--------+-------+
5 rows in Set (0.00 sec)


Mysql> select Other,bname from Boy;
+-------+--------+
| Other | bname |
+-------+--------+
| A | Cock Wire |
| B | John Doe |
| C | Harry |
| D | Ko Fu Handsome |
| E | Zheng Qi |
+-------+--------+
5 rows in Set (0.00 sec)


Mysql> #女生上台, with the other half, without the other half, with null
Mysql> #不能用左连接来做
Mysql> #用右连接. Just a girl left join male
Mysql> #用右连接, just male right join girl
Mysql> Select boy.*,girl.*
-From
Boy right Join Girl
-On boy.other = Girl.other;
+--------+-------+--------+-------+
| bname | Other | Gname | Other |
+--------+-------+--------+-------+
| John Doe | B | Stewardess | B |
| Harry | C | Big S | C |
| Ko Fu Handsome | D | Gillian | D |
| Ko Fu Handsome | D | Cecilia Cheung | D |
| Zheng Qi | E | Lin Daiyu | E |
| NULL | NULL | Bao Chai | F |
+--------+-------+--------+-------+
6 rows in Set (0.01 sec)


Mysql> Select boy.*,girl.*
-From
Boy inner JOIN Girl
-On Boy.other=girl.other;
+--------+-------+--------+-------+
| bname | Other | Gname | Other |
+--------+-------+--------+-------+
| John Doe | B | Stewardess | B |
| Harry | C | Big S | C |
| Ko Fu Handsome | D | Gillian | D |
| Ko Fu Handsome | D | Cecilia Cheung | D |
| Zheng Qi | E | Lin Daiyu | E |
+--------+-------+--------+-------+
5 rows in Set (0.00 sec)


Mysql> exit




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http://www.tudou.com/programs/view/TVhY20adVL4/

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