Aggregate Functions on subsets of data based on current row values with SQL

Posted by aasukisuki on Stack Overflow See other posts from Stack Overflow or by aasukisuki
Published on 2010-05-15T00:55:02Z Indexed on 2010/05/15 1:04 UTC
Read the original article Hit count: 319

Filed under:

mysql

|

aggregate

|

subquery

Hopefully that title makes sense...

Let's say I have an employee table:

ID | Name | Title   | Salary
----------------------------
1  | Bob  | Manager | 15285
2  | Joe  | Worker  | 10250
3  | Al   | Worker  | 11050
4  | Paul | Manager | 16025
5  | John | Worker  | 10450

What I'd like to do is write a query that will give me the above table, along with an averaged salary column, based on the employee title:

ID | Name | Title   | Salary | Pos Avg
--------------------------------------
1  | Bob  | Manager | 15285  | 15655
2  | Joe  | Worker  | 10250  | 10583
3  | Al   | Worker  | 11050  | 10583
4  | Paul | Manager | 16025  | 15655
5  | John | Worker  | 10450  | 10583

I've tried doing this with a sub-query along the lines of:

Select *, (select Avg(e2.salary) from employee e2 where e2.title = e.title) from employee e

But I've come to realize that the sub-query is executed first, and has no knowledge of the table alias'd e

I'm sure I'm missing something REALLY obvious here, can anyone point me in the right diretion?

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