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Inner join returns common records between both the tables whereas left join returns all rows from left table & the matching rows from right table.

INNER JOIN: Returns all rows when there is at least one match in BOTH tables
LEFT JOIN: Return all rows from the left table, and the matched rows from the right table
RIGHT JOIN: Return all rows from the right table, and the matched rows from the left table
FULL JOIN: Return all rows when there is a match in ONE of the tables

From W3Schools website.

Inner Join performs join on only common attributes of both the relation table.

Left is Outer Join, in which join is performed on all attributes of left table and NULL or matched rows of Right

R1(C1,C2) and R2(C1,C3)
If I do a inner join,it'll result into
r1.c1 r1.c2 r2.c1 r2.c2

And upon left join,all the entities from the above result set + the remaining from r1 will be produces as a result set.