RE: [PHP-DB] Another SELECTING problem :-(

At 12:52 PM +0100 8/9/01, Dave Watkinson wrote:

I have (many many many) tables ... two of which are linked by a third, so that there can be a one-to-many relationship. What I'd like to do is find which ids from table 1 have more than one relation in table 2, via table 3. I've tried this... SELECT empid, COUNT(empid) FROM emp_cont , employers, contacts WHERE emp_cont.empid = employers.uid and emp_cont.contid = contacts.uid and count(empid) > 1;

Your getting a lot of errors, because the statement has well a lot of mistakes. Let's start near the beginning, you state: SELECT empid, COUNT(empid) FROM emp_cont , employers, contacts This statement should produce an error, since you didn't tell the database which table to take empid from. A working statement would look like SELECT empid, COUNT(empid) FROM emp_cont or SELECT emp_cont.empid, COUNT( emp_cont.empid) FROM emp_cont , employers, contacts Either statement provides SQL with implicit instructions, as to which empid to use and where. The next major error is to use a Count function without the group by. I'm not an SQL guru, but I believe whenever you use count you must also use group by or having so adding a SELECT empid, COUNT(empid) FROM emp_cont GROUP BY empid will correct that. Unfortunately, I think the larger issue is how your trying to find your query. Your query did confuse me a little, so I could be wrong, but technically speaking, if you are trying to locate an employee with more than one record in employee contracts, then there's no need to involve the contracts table within the query. So say I have table Employees that contains empid, name, ssn. Then I have table Employee Contracts that contains, empid, contractid. Assuming that all empid(s) on Employee Contracts have a correlating empid in Employees (which they will if the table was defined properly) then the steps to get what you want are: Step 1: Return a Count of empid SELECT COUNT(empid) AS countid FROM emp_cont GROUP BY empid Step 2: Return employees with more than one contract SELECT empid FROM emp_cont WHERE countid >1 You'll note that both step requires a return, which general means a subquery, I believe for MySQL to hanle subqueries you actually have to perform to separate queries. If your not using MySQL then you could write a statement such as: SELECT empid FROM emp_cont WHERE (SELECT COUNT(empid) FROM emp_cont GROUP BY empid) [note statement may need tweaking since I use MySQL and can't test it] If your using MySQL, I believe you need to return the results from one, then use the results to find the next. Or you could use PHP to cheat, and return all results, but only display the ones where the count is greater than 1. A subquery is best if your tables are large, returning 1000 results to display 50 wastes time. But if you have under 200 employees, then just use the SQL statement $results=mysql_query ( SELECT empid, COUNT(empid) AS countid FROM emp_cont GROUP BY empid); while ($row=mysql_fetch_array($results)){ $countid = $row["countid"]; $empid = $row["empid"]; if($countid=="1") { $display_employee .=""; } else { $display_employee .=" <p>$empid</p>"; }; } ?> <? echo "$display_employee"; ?> Alnisa -- ......................................... Alnisa Allgood Executive Director Nonprofit Tech (ph) 415.337.7412 (fx) 415.337.7927 (url) http://www.nonprofit-techworld.org (url) http://www.nonprofit-tech.org (url) http://www.tech-library.org ......................................... Nonprofit Tech E-Update mailto:nonprofit-tech-subscribe@egroups.com ......................................... applying technology to transform .........................................