Complement of a SQL Join? T-SQL help needed - sql

Question

I will try to make my question sound as unconfusing as possible. I appologize in advance for any wording mistakes as I try to phrase my question as best as I can:
Using T-SQL I need to write a join statement that gets me all the results that have a match in table A and table B
AND (!)
another join statement (or a continuation of the first join) that returns all the results from table A that DID NOT have a match in table B, BUT in this second result set I need to have one of the columns set to "N/A" to identify the records that didn't have a match.
In other words, I need something that would return everything in table A but would also identify the rows that weren't matched in B. That information is then used in a report.
Here is what I have so far:
I have the first part done:
LEFT OUTER JOIN dbo.chart B
ON B.UserName = A.user_name
That gets me the matching records and just the matching records
I tried adding this second join:
JOIN dbo.chart
ON NOT EXISTS (select * from B.UserName = A.user_name)
Hoping it would get me the non-matching records (I was planning to then use REPLACE on the column of interest to label that column "N/A") but there is something clearly wrong with my synthax as that generates exceptions.
My question is what do I need to change to get me the results you need. I do know that I need to have at least one join as I have other part of the query to work with. I just don't know if I need to have that one join return both sets of data of I actually do need a second one just for the non-matching records.
Hope this wasn't too confusing. Any help would be greatly appreciated.
Thank you!
Update: I would just like to emphasize that the reason I considered using a second join instead of getting all of the results at once is because I need to correctly identify and label those rows that weren't matched within everything that I get back.

Answer 1

I'm not sure where you are going with the second join. LEFT JOIN seems to do everything you want...
DECLARE #tableA TABLE (a_id INT) INSERT INTO #tableA VALUES (1), (2), (3), (4)
DECLARE #tableB TABLE (b_id INT) INSERT INTO #tableB VALUES (2), (3)
SELECT * FROM #tableA AS A LEFT JOIN #tableB AS B on A.a_id = b.b_id
a_id | b_id
------+------
1 | NULL
2 | 2
3 | 3
4 | NULL
Unless you mean that you're actually joining 3 tables together?
DECLARE #org TABLE (o_io INT) INSERT INTO #org VALUE (2), (3), (4)
DECLARE #tableA TABLE (a_id INT) INSERT INTO #tableA VALUES (1), (2), (3), (4)
DECLARE #tableB TABLE (b_id INT) INSERT INTO #tableB VALUES (2), (3)
SELECT
*
FROM
#org AS O
INNER JOIN
#tableA AS A
ON O.o_id = A.a_id
LEFT JOIN
#tableB AS B
ON A.a_id = b.b_id
o_id | a_id | b_id
------+------+------
2 | 2 | 2
3 | 3 | 3
4 | 4 | NULL

Answer 2

Sample data:
declare #TableA table
(
TableAID int,
TableAName varchar(10)
)
declare #TableB table
(
TableBID int,
TableBName varchar(10),
TableAID int
)
insert into #TableA values
(1, 'A 1'),
(2, 'A 2'),
(3, 'A 3')
insert into #TableB values
(1, 'B 1', 1),
(2, 'B 2', 2)
N/A instead of TableBName:
select A.TableAName,
coalesce(B.TableBName, 'N/A') as TableBName
from #TableA as A
left outer join #TableB as B
on A.TableAID = B.TableAID
Result:
TableAName TableBName
---------- ----------
A 1 B 1
A 2 B 2
A 3 N/A
Extra column for N/A:
select A.TableAName,
B.TableBName,
case when B.TableBID is null
then 'N/A'
else ''
end as TableBPresent
from #TableA as A
left outer join #TableB as B
on A.TableAID = B.TableAID
Result:
TableAName TableBName TableBPresent
---------- ---------- -------------
A 1 B 1
A 2 B 2
A 3 NULL N/A

Answer 3

Try using a union:
select A.id, b.id, b.desc from tablea A LEFT OUTER JOIN dbo.chart B
ON B.UserName = A.user_name
UNION
select a.id, 0, 'N/A' from tablea where NOT EXISTS (select * from B.UserName = A.user_name)