What are the different types of connections in MySQL and how do they differ from each other?
There are three main types of joins in MySQL: inner join, outer join, and cross join.
- Inner join: only returns rows that have a match in both of the two data tables, specifically where the join keys in the tables are equal. Rows that do not have a match in both tables will not be returned.
- Outer join: An outer join can be divided into left outer join and right outer join. A left outer join will return all records from the left table, as well as matching records from the right table. A right outer join will return all records from the right table, as well as matching records from the left table. If there are no matching rows in a table, it will return a NULL value.
- Cross join: A cross join returns the Cartesian product of two tables, meaning it returns all possible combinations of the two tables. This type of join typically results in a very large result set and should be avoided on large tables.
The main difference in logic among these three types of joins is in the results returned. Inner joins only return matching rows, outer joins return matching rows as well as non-matching rows (NULL values), and cross joins return all possible combinations. In practical applications, the appropriate join type should be chosen based on specific business requirements and the relationship between data tables.
