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What is MySQL RIGHT JOIN and how do we write MySQL queries for it?

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2023-09-05 15:09:021571browse

什么是 MySQL RIGHT JOIN 以及我们如何为其编写 MySQL 查询?

It is similar to LEFT join, except that the table processing is reversed. Using a RIGHT join, every row from the right table will appear in the result set. For rows in the right table that do not match rows in the left table, the columns in the left table will display NULL. To understand it, let’s take an example of two tables named tbl_1 and tbl_2, which have the following data -

mysql> Select * from tbl_1;
+----+--------+
| Id | Name   |
+----+--------+
| 1  | Gaurav |
| 2  | Rahul  |
| 3  | Raman  |
| 4  | Aarav  |
+----+--------+
4 rows in set (0.00 sec)

mysql> Select * from tbl_2;
+----+---------+
| Id | Name    |
+----+---------+
| A  | Aarav   |
| B  | Mohan   |
| C  | Jai     |
| D  | Harshit |
+----+---------+
4 rows in set (0.00 sec)

Now, the query for RIGHT JOIN can be as follows -

mysql> SELECT tbl_1.id,tbl_2.id FROM tbl_1 RIGHT JOIN tbl_2 ON tbl_1.name = tbl_2.name;
+------+----+
| id   | id |
+------+----+
| 4    | A  |
| NULL | B  |
| NULL | C  |
| NULL | D  |
+------+----+
4 rows in set (0.00 sec)

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