Inner join:
mysql> select * from book_wangjing as book_1 inner join user_wangjing as user_1 on book_1.id=user_1.id limit 2;
+----+------------------------+-------------+-------+--------------+----+---------------------+------------+---------------------+----------+
| id | book_name | book_author | price | publish_date | id | date1 | date2 | date3 | time |
+----+------------------------+-------------+-------+--------------+----+---------------------+------------+---------------------+----------+
| 1 | Webdriver Framework Practical Guide | Mr. Wu | 100 | 2018-05-05 | 1 | 2018-05-05 00:08:24 | 2018-05-05 | :08:24|
| 2 | how google test | Mr. Li | 99 | 2018-05-05 | 2 | 2018-05-05 00:08:54 | 2018-05-05 | 08:54 |
+----+------------------------+-------------+-------+--------------+----+---------------------+------------+---------------------+----------+
2 rows in set (0.00 sec)
Left join:
mysql> select a.* from author_wangjing as a left join book_wangjing as b on a.author_name=b.book_author;
+----+-------------+--------+
| id | author_name | salary |
+----+-------------+--------+
| 1 | Mr. Wu | 10000 |
| 3 | Mr Jackson | 15000 |
| 2 | Mr. Zhang | 13000 |
+----+-------------+--------+
3 rows in set (0.07 sec)
Right join:
mysql> select * from user_wangjing as user_1 right join book_wangjing as book_1 on user_1.id=book_1.id;
+------+---------------------+------------+---------------------+----------+----+------------------------+-------------+-------+--------------+
| id | date1 | date2 | date3 | time | id | book_name | book_author | price | publish_date |
+------+---------------------+------------+---------------------+----------+----+------------------------+-------------+-------+--------------+
| 1 | 2018-05-05 00:08:24 | 2018-05-05 | 2018-05-05 00:08:24 | 00:08:24 | 1 | Webdriver Framework Practical Guide | Mr. Wu | 100 | 2018 -05-05 |
| 2 | 2018-05-05 00:08:54 | 2018-05-05 | 2018-05-05 00:08:54 | 00:08:54 | 2 | how google test | Mr. Li | 99 | 2018- 05-05 |
| 3 | 2018-05-05 00:08:55 | 2018-05-05 | 2018-05-05 00:08:55 | 00:08:55 | 3 | unit test | Mr. Li | 1 | 2018-05 -05 |
| 4 | 2018-05-05 00:08:56 | 2018-05-05 | 2018-05-05 00:08:56 | 00:08:56 | 4 | function test | Mr. Li | 10 | 2017-11 -10 |
| NULL | NULL | NULL | NULL | NULL | 5 | function test | Mr Jackson | 10 | 2013-06-10 |
+------+---------------------+------------+---------------------+----------+----+------------------------+-------------+-------+--------------+
5 rows in set (0.07 sec)
mysql> select a.* from author_wangjing as a right join book_wangjing as b on a.author_name=b.book_author;
+------+-------------+--------+
| id | author_name | salary |
+------+-------------+--------+
| 1 | Mr. Wu | 10000 |
| 3 | Mr Jackson | 15000 |
| NULL | NULL | NULL |
| NULL | NULL | NULL |
| NULL | NULL | NULL |
+------+-------------+--------+
union：
mysql> select book_author from book_wangjing union select author_name from author_wangjing;
+-------------+
| book_author |
+-------------+
| Teacher Wu |
| Mr. Li |
| Mr Jackson |
| Teacher Zhang |
+-------------+
4 rows in set (0.06 sec)
1. Inner join: a.author_name and b.book_author appearing in the result set must exist in both tables at the same time
2. Left join: a.author_name in the result set must exist in the left table (author_wangjing table) and be displayed in all
3. Right join: b.book_author that appears in the result set must exist in the right table (book_wangjing table) and display all
4. union: for merging, when using union, the data columns of the left table should be as many as the data columns of the right table