If there are three records in the first table and three in the second, how many records will be returned by a left join?

When performing a LEFT JOIN, the number of records in the result depends on the number of records in the left (first) table and the matches with the right (second) table.

If the first table has 3 records, and the second also has 3 records, then the result of the LEFT JOIN will be at least 3 records — one for each record from the left table.

If each record from the left table has a match in the right table, then there will be exactly 3 records.

If some records from the left table do not have matches, then for those records, the result set will contain NULL values from the right table, but the number of records will remain 3.

In conclusion: in a LEFT JOIN, the number of records equals the number of records in the left table, which is 3.