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

When using a left join to connect two tables, the concepts of left table and right table are introduced, and a join predicate is also required. It returns all rows in the left table, including rows that satisfy the join predicate and rows that do not.

For rows that do not match the join-predicate, NULL will appear in the column of the right table in the result set. 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 LEFT JOIN can be as follows -

mysql> SELECT tbl_1.id,tbl_2.id FROM tbl_1 LEFT JOIN tbl_2 ON tbl_1.name = tbl_2.name;
+----+------+
| id | id   |
+----+------+
| 1  | NULL |
| 2  | NULL |
| 3  | NULL |
| 4  | A    |
+----+------+
4 rows in set (0.02 sec)

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