subquery using IN clause

Question

----------
User
----------
user_ID(pk)
UserEmail

----------
Employer1
----------
Emp1ID(pk)
Emp1NO

----------
Employer2
----------
Emp2ID(pk)
Emp2NO

----------
Pr         


        

Answer 1

You can only return one column from your subquery. If you just want both the employee ID and manager ID consider a union query as your subquery:

    emp.Emp2NO IN
(select ProjEmpID from project
 union
 select ProjEmpMGRID from project)

or rewriting to use two IN queries with separate subqueries for each.

Answer 2

emp.Emp2NO IN
 (select ProjEmpID from project) or (select ProjEmpMGRID from project)

Hope you will understant why it should be so. u can put a mail to me at gnmsr@ap.nic.in

Ok i will expalin. Emp1NO is one value chcked with every value in the list of values return by a single column values where as ur query returns a matrix of many(no. of rows) X 2

Answer 3

I would recommend not using the IN statement. Use EXISTS instead.

http://www.techonthenet.com/sql/exists.php

Example #1

Answer 4

Eric Hauser is correct - you can't specify two columns in SELECT contained in an IN clause to one column outside.

That said, I re-wrote your query so you don't need to use UNIONs at all:

SELECT DISTINCT u.user_email
  FROM USERS u
  JOIN EMPLOYER e ON u.user_id IN (e.emp1id, e.emp2id) 
  JOIN PROJECT p ON e.emp1no IN (p.projempid, p.projempmgrid)
                 OR e.emp2no IN (p.projempid, p.projempmgrid)

I also changed the query to use ANSI-92 JOIN syntax - your original uses ANSI-89.