首先默認你已經安裝好mysql

• 導數數據 代碼鏈接

mysql> create database joinn; # 創建數據庫 mysql> use joinn; # 使用已創建的數據庫 mysql> set names utf8; # 設置編碼 mysql> source /home/lg/lg/mysql_better/join_learn/runoob-mysql-join-test.sql # 注意要把你的目錄切換mysql> use joinn; mysql> show tables; +-----------------+ | Tables_in_joinn | +-----------------+ | runoob_tbl | | tcount_tbl | +-----------------+ 2 rows in set (0.00 sec)

首先看著下這兩個表的數據

mysql> select * from runoob_tbl; +-----------+---------------+---------------+-----------------+ | runoob_id | runoob_title | runoob_author | submission_date | +-----------+---------------+---------------+-----------------+ | 1 | 學習 PHP | 菜鳥教程 | 2017-04-12 | | 2 | 學習 MySQL | 菜鳥教程 | 2017-04-12 | | 3 | 學習 Java | RUNOOB.COM | 2015-05-01 | | 4 | 學習 Python | RUNOOB.COM | 2016-03-06 | | 5 | 學習 C | FK | 2017-04-05 | +-----------+---------------+---------------+-----------------+

mysql> select * from tcount_tbl;

+---------------+--------------+ | runoob_author | runoob_count | +---------------+--------------+ | 菜鳥教程 | 10 | | RUNOOB.COM | 20 | | Google | 22 | +---------------+--------------+ 3 rows in set (0.01 sec)

inner join

mysql> SELECT a.runoob_id, a.runoob_author, b.runoob_count FROM runoob_tbl a INNER JOIN tcount_tbl b ON a.runoob_author = b.runoob_author; +-----------+---------------+--------------+ | runoob_id | runoob_author | runoob_count | +-----------+---------------+--------------+ | 1 | 菜鳥教程 | 10 | | 2 | 菜鳥教程 | 10 | | 3 | RUNOOB.COM | 20 | | 4 | RUNOOB.COM | 20 | +-----------+---------------+--------------+ 4 rows in set (0.00 sec)

from 后面我加了一個括號，可以理解一個整體

mysql> SELECT a.runoob_id, a.runoob_author, b.runoob_count FROM (runoob_tbl a INNER JOIN tcount_tbl b ON a.runoob_author = b.runoob_author); +-----------+---------------+--------------+ | runoob_id | runoob_author | runoob_count | +-----------+---------------+--------------+ | 1 | 菜鳥教程 | 10 | | 2 | 菜鳥教程 | 10 | | 3 | RUNOOB.COM | 20 | | 4 | RUNOOB.COM | 20 | +-----------+---------------+--------------+ 4 rows in set (0.00 sec)

等價下面的where 語句

mysql> SELECT a.runoob_id, a.runoob_author, b.runoob_count FROM runoob_tbl a, tcount_tbl b WHERE a.runoob_author = b.runoob_author; +-----------+---------------+--------------+ | runoob_id | runoob_author | runoob_count | +-----------+---------------+--------------+ | 1 | 菜鳥教程 | 10 | | 2 | 菜鳥教程 | 10 | | 3 | RUNOOB.COM | 20 | | 4 | RUNOOB.COM | 20 | +-----------+---------------+--------------+ 4 rows in set (0.00 sec)

leftjoin

mysql> SELECT a.runoob_id, a.runoob_author, b.runoob_count FROM runoob_tbl a LEFT JOIN tcount_tbl b ON a.runoob_author = b.runoob_author; +-----------+---------------+--------------+ | runoob_id | runoob_author | runoob_count | +-----------+---------------+--------------+ | 1 | 菜鳥教程 | 10 | | 2 | 菜鳥教程 | 10 | | 3 | RUNOOB.COM | 20 | | 4 | RUNOOB.COM | 20 | | 5 | FK | NULL | +-----------+---------------+--------------+

rightjoin

mysql> SELECT a.runoob_id, a.runoob_author, b.runoob_count FROM runoob_tbl a right JOIN tcount_tbl b ON a.runoob_author = b.runoob_author; +-----------+---------------+--------------+ | runoob_id | runoob_author | runoob_count | +-----------+---------------+--------------+ | 1 | 菜鳥教程 | 10 | | 2 | 菜鳥教程 | 10 | | 3 | RUNOOB.COM | 20 | | 4 | RUNOOB.COM | 20 | | NULL | NULL | 22 | +-----------+---------------+--------------+ 5 rows in set (0.00 sec)

下面這段sql 是兩張表的笛卡爾積

mysql> SELECT * from tcount_tbl,runoob_tbl; +---------------+--------------+-----------+---------------+---------------+-----------------+ | runoob_author | runoob_count | runoob_id | runoob_title | runoob_author | submission_date | +---------------+--------------+-----------+---------------+---------------+-----------------+ | 菜鳥教程 | 10 | 1 | 學習 PHP | 菜鳥教程 | 2017-04-12 | | RUNOOB.COM | 20 | 1 | 學習 PHP | 菜鳥教程 | 2017-04-12 | | Google | 22 | 1 | 學習 PHP | 菜鳥教程 | 2017-04-12 | | 菜鳥教程 | 10 | 2 | 學習 MySQL | 菜鳥教程 | 2017-04-12 | | RUNOOB.COM | 20 | 2 | 學習 MySQL | 菜鳥教程 | 2017-04-12 | | Google | 22 | 2 | 學習 MySQL | 菜鳥教程 | 2017-04-12 | | 菜鳥教程 | 10 | 3 | 學習 Java | RUNOOB.COM | 2015-05-01 | | RUNOOB.COM | 20 | 3 | 學習 Java | RUNOOB.COM | 2015-05-01 | | Google | 22 | 3 | 學習 Java | RUNOOB.COM | 2015-05-01 | | 菜鳥教程 | 10 | 4 | 學習 Python | RUNOOB.COM | 2016-03-06 | | RUNOOB.COM | 20 | 4 | 學習 Python | RUNOOB.COM | 2016-03-06 | | Google | 22 | 4 | 學習 Python | RUNOOB.COM | 2016-03-06 | | 菜鳥教程 | 10 | 5 | 學習 C | FK | 2017-04-05 | | RUNOOB.COM | 20 | 5 | 學習 C | FK | 2017-04-05 | | Google | 22 | 5 | 學習 C | FK | 2017-04-05 | +---------------+--------------+-----------+---------------+---------------+-----------------+ 15 rows in set (0.00 sec)

總結

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