Inner Join returned values

Question

I have a query such as,

select name 

from employee 

inner join task on employee.id = task.employee_id 

order by name asc 

Tables look like:

employee

id name 

1 Emily 

2 Sam 

3 AI 

4 Joe 

5 Daniel 

6 John

task

task_id employee_id

 A123       1 

 D456       3 

 A122       1 

I believed the original query above would result in:

Al
Emily

But it is actually:

Al
Emily
Emily

I thought it would just return Emily once since inner join returns both values in both tables, but doesnt Emily appear only once in the employee table? I dont understand why it returns Emily twice even though it is listed twice in the task table?

Thanks

Answer 1

Emily has two tasks, hence her name record gets duplicated in the join, once for each match. I might use exists logic to get the result you want here:

SELECT e.name
FROM employee e
WHERE EXISTS (SELECT 1 FROM task t WHERE t.employee_id = e.id);

Read in plain English, the above query says to return any employee name (once) for which we can find at least one task in the task table.