What would be the output of a left join? Suppose the master table is A and the other table is B. If we perform a left join, what would be the output?

A left join (or left outer join) returns all rows from the left (master) table, and the matching rows from the right (joined) table. For each row in the left table, the database searches for rows in the right table that satisfy the join condition. If a match is found, the columns from both tables are combined into a single result row. If no match is found, the columns from the right table are filled with NULLs, but the left table’s row still appears in the result.

For example, if table A has rows (1, 'Alice'), (2, 'Bob'), (3, 'Carol') and table B has rows (1, 'NY'), (3, 'LA'), a left join on the first column would produce:

1, 'Alice', 'NY'

2, 'Bob', NULL

3, 'Carol', 'LA'

Thus, the output preserves all rows from A, with B’s data where available, and NULLs where there is no matching key in B.