Left join results in extra records - sql-server

Question

This is a basic left join problem and I have read many articles explaining what is going on but somehow the resolution is not clicking in my head. My left table has unique records. My right table has several records for each record in the left.
In the articles I have been reading this is often explained as left table has customers and right table has orders. That is very similar but not exactly what I am facing.
In my situation the left table has unique records and the right has repetitive data to be migrated into db the left table is in. So I am trying to write a query that will join on the key shared by both but I only need one record from the right. The results I am getting of course have multiple records since the single left matches multiple times on the right.
I am thinking I need to add some sort of filtering such as Top(1) but still reading / learning and wanted to get feedback / direction from the brainiacs on this list.
Here is a simple schema of what I am working with:
DECLARE #Customer TABLE
(
Id int,
Name varchar(50),
email varchar(50)
)
INSERT #Customer VALUES(1, 'Frodo', 'frodo#middleearth.org')
INSERT #Customer VALUES(2, 'Bilbo', 'Bilbo#middleearth.org')
INSERT #Customer VALUES(3, 'Galadriel', 'Galadriel#middleearth.org')
INSERT #Customer VALUES(4, 'Arwen', 'Arwen#middleearth.org')
INSERT #Customer VALUES(5, 'Gandalf', 'Gandalf#middleearth.org')
DECLARE #CustomerJobs TABLE
(
Id int,
email varchar(50),
jobname varchar(50)
)
INSERT #CustomerJobs VALUES(1, 'frodo#middleearth.org', 'RingBearer')
INSERT #CustomerJobs VALUES(2, 'frodo#middleearth.org', 'RingBearer')
INSERT #CustomerJobs VALUES(3, 'frodo#middleearth.org', 'RingBearer')
INSERT #CustomerJobs VALUES(4, 'frodo#middleearth.org', 'RingBearer')
INSERT #CustomerJobs VALUES(5, 'frodo#middleearth.org', 'RingBearer')
INSERT #CustomerJobs VALUES(6, 'Bilbo#middleearth.org', 'Burglar')
INSERT #CustomerJobs VALUES(7, 'Bilbo#middleearth.org', 'Burglar')
INSERT #CustomerJobs VALUES(8, 'Bilbo#middleearth.org', 'Burglar')
INSERT #CustomerJobs VALUES(9, 'Galadriel#middleearth.org', 'MindReader')
INSERT #CustomerJobs VALUES(10, 'Arwen#middleearth.org', 'Evenstar')
INSERT #CustomerJobs VALUES(10, 'Arwen#middleearth.org', 'Evenstar')
INSERT #CustomerJobs VALUES(11, 'Gandalf#middleearth.org', 'WhiteWizard')
INSERT #CustomerJobs VALUES(12, 'Gandalf#middleearth.org', 'WhiteWizard')
SELECT
Cust.Name,
Cust.email,
CJobs.jobname
FROM
#Customer Cust
LEFT JOIN #CustomerJobs CJobs ON
Cjobs.email = Cust.email
I'm toying with row_number over partition() as maybe I should be joining to a cte with the row_number over partition instead of the table itself???
One other constraint I have is I can't delete the duplicates from the right table.
So again my apologies for the simplistic question and thank you for the help.

Answer 1

Instead of using a left join, use an outer apply... you can then use the top clause to limit the rows returned...
select
Cust.Name
, Cust.email
, CJobs.jobname
from #Customer Cust
outer apply (
select top 1 *
from #CustomerJobs CJobs
where Cjobs.email = Cust.email
) cjobs;

Answer 2

You have to come up with some artificial method of reducing the second table to one row per email. For example:
SELECT
Cust.Name,
Cust.ID,
Cust.email,
CJobs.jobname
FROM
#Customer Cust
LEFT JOIN
(select min(id) as id,email, jobname
from
#CustomerJobs
group by email, jobname) as CJobs ON
Cjobs.email = Cust.email
But that's pretty much random. Is there a way to determine which row from your CustomerJobs table is the "right" one?

Answer 3

SELECT DISTINCT
Cust.Name,
Cust.email,
CJobs.jobname
FROM
#Customer Cust
LEFT JOIN #CustomerJobs CJobs ON
Cjobs.email = Cust.email
The additional of the DISTINCT keyword should get you what you want.

Answer 4

This will work:
SELECT
Cust.Name,
Cust.ID,
Cust.email,
CJobs.jobname
FROM #Customer Cust
LEFT JOIN
(SELECT DISTINCT email, jobname
FROM #CustomerJobs) C2 ON C2.email = C.email