Re: Combining two SQL Statements

gonnot_at_gmx.de (Michael) wrote in message news:<89cf72b0.0410070017.26d34736_at_posting.google.com>...
> Hello,
> I need to combine this two SQL-Statements to one SQL:
>
> 1. select UserId, UsedSlots from user_used_slots;
>
> UserId UsedSlots
> a 3
> b 5
> a 4
> c 3
> b 5
>
> 2. select UserId, FreeSlots from user_free_slots;
>
> UserId FreeSlots
> a 4
> b 5
> b 3
> c 3
> b 5
>
> ==> The resulting SQL-Staetement should show something like this:
> (TotalSlots = UsedSlots + FreeSlots)
>
> UserId UsedSlots FreeSlots TotalSlots
> a 7 4 11
> b 10 15 25
> c 3 3 6
>
> How can I produce a Output which calculates everything correctly??
> Thanks,
> Michael

Here's a hint which is actually a good general principle to follow. Even experienced developers can benefit from being reminded of this. Here it is:

<HINT>
This is a relational database and as such, everything is a table (or set).
Even the results of a query are a table. </HINT>

So think of the problem that way. Imagine writing the final query from two tables which hold the free slots and used slots by user, as listed above. Once you can write that, look up in-line views or subqueries in your SQL manual.

  HTH,
 ed Received on Thu Oct 07 2004 - 12:39:14 CDT