SQL Query to merge several views into one - sql

Question

I was trying to create a new view out of 3 or 4 other views/tables.
TableA:
title_id
homeTeam
1234
WSV
5678
SSV
7890
NULL
4321
SCC
TableB:
title_id
awayTeam
1234
SSV
5678
SFV
7890
NULL
4321
KFC
TableC:
title_id
homeTeam
1234
SSV
5678
NULL
7890
AAB
4711
BFG
I would like to generate a new view out of those three which looks like:
title_id
Teams
1234
WSV, SSV, SSV
5678
SSV, SFV, N/A
7890
N/A, N/A, AAB
4321
SCC, KFC, N/A
4711
N/A, N/A, BFG
As you can see, NULL should be renamed to N/A, as well if id doesn't exist in one of the other tables. And I would like to get DISTINCT title_id.
#DaleK sure, i tried it like this:
select tableA.title_id, ISNULL(tableA.homeTeam, 'N/A') + ',' +
ISNULL(tableB.awayTeam, 'N/A') + ',' + ISNULL(tableC.homeTeam, 'N/A')
as Teams from tableA, tableB, tableC;
This leads into an neverending query for my tables which has each more than 300k rows.
Next i tried join:
select tableA.title_id, ISNULL(tableA.homeTeam, 'N/A') + ',' +
ISNULL(tableB.awayTeam, 'N/A') + ',' + ISNULL(tableC.homeTeam, 'N/A')
as Teams from tableA FULL JOIN tableB ON tableB.title_id =
tableA.title_id FULL JOIN tableC ON tableC.title_id = tableA.tile_id
But to be honest i wasnt sure about the number of rows.

Answer 1

You can UNION ALL the tables together, then use string aggregation
SELECT
t.title_id,
STRING_AGG(ISNULL(t.team, 'N/A'), ', ') WITHIN GROUP (ORDER BY t.ordering) AS team
FROM (
SELECT
a.title_id,
a.homeTeam AS team,
1 AS ordering
FROM TableA a
UNION ALL
SELECT
b.title_id,
b.awayTeam,
2
FROM TableB b
UNION ALL
SELECT
c.title_id,
c.homeTeam,
3
FROM TableC c
) t
GROUP BY
t.title_id;
For SQL Server 2016 and earlier, you have to use the FOR XML method, and it's less efificent as you have to query the tables multiple times
WITH t AS (
SELECT
a.title_id,
a.homeTeam AS team,
1 AS ordering
FROM TableA a
UNION ALL
SELECT
b.title_id,
b.awayTeam,
2
FROM TableB b
UNION ALL
SELECT
c.title_id,
c.homeTeam,
3
FROM TableC c
)
SELECT
tOuter.title_id,
STUFF(tInner.team.value('text()[1]', 'nvarchar(max)'), 1, LEN(', '), '') AS team
FROM (
SELECT DISTINCT t.title_id
FROM t
) tOuter
CROSS APPLY (
SELECT ', ' + ISNULL(t.team, 'N/A')
FROM t
WHERE t.title_id = tOuter.title_id
ORDER BY t.ordering
FOR XML PATH(''), TYPE
) tInner(team);
db<>fiddle

Answer 2

Try this:
select
COALESCE(a.title_id,b.title_id,c.title_id),
CONCAT(
ISNULL(a.homeTeam,'N/A'),
ISNULL(b.awayTeam,'N/A'),
ISNULL(c.homeTeam,'N/A'),
) 'Teams',
from TableA a
full join TableB b on a.title_id = b.title_id
full join TableC c on c.title_id = a.title_id
where
a.homeTeam is not null
OR b.awayTeam is not null
OR c.homeTeam is not null
group by a.title_id
As for the DISTINCT title_id, it should be unique by default as I assume it is used as the key in each of the tables.