SQL Joining tables with 'constants' - sql

Question

I have a table of orders,
Invoice Location Customer Code SalesPersonEmail
------------------------------------------------------
300001 001 CUS001 ?
300002 006 CUS002 ?
And a table of email groups,
Role Email
-----------------------------------------------------
Filtered_Group Management#gmail.com;john#gmail.com
When Location = 001, SalesPersonEmail must be the Email field from Filtered_Group
SalesPersonEmail for all other locations must be "Orders#gmail.com;" + the Email for Role No_Filter_Group.
I'm currently using the following to achieve this,
SELECT i.Invoice, i.Location, i.[Customer Code],
CASE WHEN i.Location = 001
THEN f.Email
ELSE N'Orders#gmail.com;' + nf.Email as SalesPersonEmail
END
FROM Invoice i, RoleCodes f, RoleCodes nf
WHERE f.Role = N'Filtered_Group' AND nf.Role = N'No_Filter_Group'
My problem is the Role No_Filter_Group may not exist in the Role table at times, which causes the above query to return nothing.
How do I join these tables properly so if No_Filter_Group does not exist in the table, rows that have a SalesPersonEmail of Filtered_Group are still returned from the query?
Thanks

Answer 1

A relatively simple way is to use LEFT JOIN and put the special number 001 for your location and special role names Filtered_Group and No_Filter_Group in the join condition.
In this SQL Fiddle you can comment/uncomment one line in the schema definition to see how it works when RoleCodes has a row with No_Filter_Group and when it doesn't.
In any case, the query would return all rows from Invoice table.
SELECT
Invoice.Invoice
,Invoice.Location
,Invoice.[Customer Code]
,CASE WHEN Invoice.Location = '001'
THEN RoleCodes.Email
ELSE 'Orders#gmail.com;' + ISNULL(RoleCodes.Email, '')
END AS SalesPersonEmail
FROM
Invoice
LEFT JOIN RoleCodes ON
(Invoice.Location = '001'
AND RoleCodes.Role = 'Filtered_Group')
OR
(Invoice.Location <> '001'
AND RoleCodes.Role = 'No_Filter_Group')

Answer 2

Try something like this.
Note: This is just a example am not sure about the tables and column of your schema. Replace with the respective tables and columns
SELECT CASE
WHEN location = '001' THEN (SELECT TOP 1 email
FROM email_table
WHERE [role] = 'Filtered_Group')
ELSE 'Orders#gmail.com;'
END
FROM orders
If email_table table will have only one row for [role] = 'Filtered_Group' then you can remove the TOP 1 from the sub-query

Answer 3

Left join or an easier, albeit less efficient method would be to do a subquery in the select statement itself.
SELECT i.Invoice, i.Location, i.[Customer Code],
CASE WHEN i.Location = 001
THEN (SELECT TOP 1 f.Email FROM RoleCodes f WHERE f.Role = N'Filtered_Group')
ELSE N'Orders#gmail.com;' + ISNULL( (SELECT nf.Email as SalesPersonEmail FROM RoleCodes nf WHERE nf.Role = N'No_Filter_Group'), '')
END
FROM Invoice i
Normally you would want to join these in on each other but I'm not certain how you would do that with the schema provided.

Answer 4

Nested select will be run for each row, instead, you could try this :-
Select i.Invoice
,i.Location
,i.CustomerCode
,Isnull(r.Email,'Orders#gmail.com') As SalesPersonEmail
From Invoice As i With (Nolock)
Left Join
(
Select rc.Email
,'001' As Location
From RoleCodes As rc With (Nolock)
Where rc.Role = 'Filtered_Group'
) As r On i.Location = r.Location

Answer 5

use the following Query:
select t.Invoice,t.Location,t.[Customer Code],
case t.Location
when '001' then
t2.Email
else
'Orders#gmail.com'
end
as
Salespersonemail
from orders t
join email_groups t2 on t2.Role='Filtered_Group'