The LEFT JOIN clause is used to join two or more tables together. The main table will return all of its rows and the matching rows from the joining tables. If the joining tables don’t have the matching rows then MySQL will use NULL to represent those rows.
SELECT t1.c1, t1.c2, t2.c1, t2.c2 FROM main_table_name t1 LEFT JOIN table2 t2 ON t1.c1 = t2.c1;
Basically, you are getting everything from the main table and the matching rows from the joining tables.
Note that if LEFT JOIN is used with WHERE or/and HAVING then all rows must satisfy all conditions.