What are other ways to get this result set - sql-server

Question

What are other ways to get the same result set
I am using 4 tables
SELECT * FROM Terminal
SELECT * FROM Customer
SELECT * FROM Contract
SELECT * FROM ExternalTable
Data in these 4 tables are as below:
The query that i've written is
select ex.TerminalName,ex.CustomerName from ExternalTable ex
except
select t.TerminalName,ct.CustomerName from [Contract] c
inner join Terminal t on t.TerminalID=c.TerminalID
inner join Customer ct on ct.CustomerId=c.CustomerId
Which gets the below result
So just curious to know what are the other ways to get this same result

Answer 1

I'm not really what you are looking for, but here is another way to write the query that should produce the same results:
SELECT
ex.TerminalName,
ex.CustomerName
FROM
ExternalTable ex
WHERE
NOT EXISTS( SELECT
NULL
FROM
[Contract] c
INNER JOIN
Terminal t on t.TerminalID = c.TerminalID
INNER JOIN
Customer ct on ct.CustomerId = c.CustomerId
WHERE
t.TerminalName = ex.TerminalName
AND
ex.CustomerName = ct.CustomerName
)

Answer 2

This ought to be equivalent:
select ex.TerminalName,ex.CustomerName
from
ExternalTable ex
left outer join
(
[Contract] c
inner join Terminal t
on t.TerminalID=c.TerminalID
inner join Customer ct
on ct.CustomerId=c.CustomerId
)
on ex.TerminalName = t.TerminalName and ex.CustomerName = ct.CustomerName
where t.TerminalName is null and ct.CustomerName is null
You should note that except returns distinct results and to be strictly equivalent I would need to specify select distinct.

Answer 3

Here is a self-contained example that shows two alternatives.
One uses NOT IN, and the other uses a LEFT OUTER JOIN, but they should be equivalent.
--set up temp tables with dummy data to replicate the issue
declare #Terminal table(terminalid int,terminalname nvarchar(100));
insert into #Terminal select 1,'Terminal1' union select 2,'Terminal2'
declare #Customer table(customerid int,customername nvarchar(100));
insert into #Customer select 1,'Customer1' union select 2,'Customer2';
declare #Contract table(contractid int,terminalid int,customerid int,contractname nvarchar(100));
insert into #Contract select 1,1,1,'Contract1';
declare #ExternalTable table(externalid int,terminalname nvarchar(100),customername nvarchar(100),contractname nvarchar(100));
insert into #ExternalTable select 1,'Terminal1','Customer1','Contract1' union select 2,'Terminal2','Customer1','Contract1'
--SELECT * FROM #Terminal
--SELECT * FROM #Customer
--SELECT * FROM #Contract
--SELECT * FROM #ExternalTable
--goal: show records that are in the external table, but are not fully linked in the other tables
--original
select ex.TerminalName,ex.CustomerName from #ExternalTable ex
except
select t.TerminalName,ct.CustomerName from #Contract c
inner join #Terminal t on t.TerminalID=c.TerminalID
inner join #Customer ct on ct.CustomerId=c.CustomerId
--revised (left outer join method)
select et.TerminalName,et.CustomerName
from
#ExternalTable et
left join (
select ex.externalid
from
#Contract c
inner join #Terminal t on t.TerminalID=c.TerminalID
inner join #Customer ct on ct.CustomerId=c.CustomerId
inner join #ExternalTable ex on ex.terminalname = t.terminalname and ex.customername = ct.customername
) excludes on excludes.externalid = et.externalid
where excludes.externalid is null
--revised ("not in" method)
select et.TerminalName,et.CustomerName
from
#ExternalTable et
where et.externalid not in(
select ex.externalid
from
#Contract c
inner join #Terminal t on t.TerminalID=c.TerminalID
inner join #Customer ct on ct.CustomerId=c.CustomerId
inner join #ExternalTable ex on ex.terminalname = t.terminalname and ex.customername = ct.customername
)