Sub query in t sql select statement - sql

Question

I have a query which lists users but it requires a sub query to get whether they are available today. I need the fourth column 'Availability' to iterate through each user and display if they have availability or display a null. I've tried everything I can think of sub queries, cursors etc but no joy. Any pointers welcome!
SELECT inter.authno,
inter.FirstName,
inter.Surname,
COALESCE((
Select at.typeName as [Availability]
FROM [database].[dbo].[Interviewer] inter
full join [database].[dbo].[availability] av
on inter.authno = av.authno
full join [database].[dbo].[availability_days] ad
on av.availID = ad.availID
full join [database].[dbo].[availibiltyType] at
on av.typeID = at.typeid
where exists(
select authno
from [database].[dbo].[Interviewer]
)
and ad.actualDay = '2015-05-21'
), null ) AS [Availability]
FROM [database].[dbo].[Interviewer] inter
The query gives the below results, but it should only show Available for Harry Kane and the rest should be null.
authno FirstName Surname Availability
-------------------------------------
10 Minch Yoda Available
11 Darth Vadar Available
12 Darth Maul Available
14 Obi Wan Kenobi Available
15 Qui-Gon Jinn Available
16 Darth Sidious Available
17 Boba Fett Available
24 Harry Kane Available
39 mark o'neill Available
I also tried the code suggestion below kindly provided which gives some results I need, but it shows all of the results instead of the availability type for today.
SELECT
inter.authno,
inter.FirstName,
inter.Surname,
at.typeName as [Availability]
FROM [database].[dbo].[Interviewer] inter
left JOIN [database].[dbo].[availability] av
on inter.authno = av.authno
left JOIN [database].[dbo].[availability_days] ad
on av.availID = ad.availID
and ad.actualDay = '2015-07-21'
left JOIN [database].[dbo].[availibiltyType] at
on av.typeID = at.typeid
Output:
+----+---------+-----------+--------------+
| 10 | Minch | Yoda | NULL |
+----+---------+-----------+--------------+
| 11 | Darth | Vadar | NULL |
| 12 | Darth | Maul | NULL |
| 13 | Luke | Skywalker | NULL |
| 14 | Obi Wan | Kenobi | NULL |
| 15 | Qui-Gon | Jinn | Annual Leave |
| 16 | Darth | Sidious | NULL |
| 17 | Boba | Fett | UO |
| 17 | Boba | Fett | Available |
| 18 | test22 | test33 | NULL |
| 19 | test7 | test7 | NULL |
| 22 | Bob | Marley | NULL |
| 23 | JO | JO | NULL |
| 24 | Harry | Kane | Annual Leave |
| 24 | Harry | Kane | Available |
| 24 | Harry | Kane | Available |
| 24 | Harry | Kane | Annual Leave |
| 24 | Harry | Kane | Annual Leave |
| 24 | Harry | Kane | NW |
| 24 | Harry | Kane | NW |
| 24 | Harry | Kane | Available |
| 39 | mark | o'neill | US |
+----+---------+-----------+--------------+
I also tried the below which gets me the exact results that I need only that, I need to display all users whether they have a date in the table or not. i.e. If I change the date to last weer Harry Kane disappears.
SELECT
inter.authno,
inter.FirstName,
inter.Surname,
at.typeName as [Availability]
FROM [database].[dbo].[Interviewer] inter
left JOIN [database].[dbo].[availability] av
on inter.authno = av.authno
left JOIN [database].[dbo].[availability_days] ad
on av.availID = ad.availID
left JOIN [database].[dbo].[availibiltyType] at
on av.typeID = at.typeid
where ad.actualDay = '2015-05-21'or ad.actualDay is null
Output for today:
+--------+-----------+-----------+--------------+
| authno | FirstName | Surname | Availability |
+--------+-----------+-----------+--------------+
| 10 | Minch | Yoda | NULL |
| 11 | Darth | Vadar | NULL |
| 12 | Darth | Maul | NULL |
| 13 | Luke | Skywalker | NULL |
| 14 | Obi Wan | Kenobi | NULL |
| 16 | Darth | Sidious | NULL |
| 18 | test22 | test33 | NULL |
| 19 | test7 | test7 | NULL |
| 22 | Bob | Marley | NULL |
| 23 | JO | JO | NULL |
| 24 | Harry | Kane | Available |
+--------+-----------+-----------+--------------+
Output for 2015-05-10
+--------+-----------+-----------+--------------+
| authno | FirstName | Surname | Availability |
+--------+-----------+-----------+--------------+
| 10 | Minch | Yoda | NULL |
| 11 | Darth | Vadar | NULL |
| 12 | Darth | Maul | NULL |
| 13 | Luke | Skywalker | NULL |
| 14 | Obi Wan | Kenobi | NULL |
| 16 | Darth | Sidious | NULL |
| 18 | test22 | test33 | NULL |
| 19 | test7 | test7 | NULL |
| 22 | Bob | Marley | NULL |
| 23 | JO | JO | NULL |
+--------+-----------+-----------+--------------+

Answer 1

If I understand correctly, you want a correlated subquery for your version of the query:
SELECT inter.authno,
inter.FirstName,
inter.Surname,
(Select at.typeName as [Availability]
FROM [database].[dbo].[availability] av join
[database].[dbo].[availability_days] ad
on av.availID = ad.availID join
[database].[dbo].[availibiltyType] at
on av.typeID = at.typeid
where inter.authno = av.authno and ad.actualDay = '2015-05-21'
) AS [Availability]
FROM [database].[dbo].[Interviewer] inter;
Some notes:
COALESCE(<x>, NULL) doesn't make sense. Just use <X>
With a subquery, you should use IFNULL() rather than COALESCE(), because SQL Server has (what I consider to be) a flawed implementation of COALESCE().
Your subquery needs to be correlated to the outer query.
I have no idea what the EXISTS clause was supposed to do. If the table has any rows, then it would always return TRUE.
There is no reason for full joins in the subquery.
I would expect your version to return the error "subquery returns more than one row".

Answer 2

Without seeing your table structure It's a guess, but an educated one.
Try this:
SELECT inter.authno,
inter.FirstName,
inter.Surname,
at.typeName as [Availability]
FROM [database].[dbo].[Interviewer] inter
LEFT JOIN [database].[dbo].[availability] av on inter.authno = av.authno
LEFT JOIN [database].[dbo].[availability_days] ad on av.availID = ad.availID and ad.actualDay = '2015-05-21'
LEFT JOIN [database].[dbo].[availibiltyType] at on av.typeID = at.typeid
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