Introduction to SQL joins

- [Instructor] The SQL join clause allows us to combine recommend codes from two tables. A join in SQL locates related column values across two or more tables. So for example, assume that we have an employees table as well as a departments table. And lets say, in our example, we would like to retrieve the employee ID, employee name. But instead of retrieving the department number from the employee table, which makes little sense.

I mean, what's department 20, right? So assuming that instead of retrieving the department number we want to retrieve the department name. But the department name column exists in the departments table, not in the employees table. Using a SQL join, we can choose which column links both tables together, department number in our case. And produce a unified result, combining data from the two tables together.

So in our case we can choose to display the employee ID and employee name from the employees table but display the department name from the departments table. We will see joins in action throughout this chapter so don't worry if it all seems a little bit to theoretical for now. Also note that there are multiple types of joins you can use in your SQL quarries. These include inner joins, left joins, right joins, and full outer joins.

Inner joins will select records that have matching values in both tables. Left join will select records from the first table with any matching records from the right table. A right join selects records from the second that is right most table, with matching rows from the left most table. And a full outer join selects all records that match from in the left or right tables. So don't sweat it. We'll see all of this in action throughout our chapter.