How to correctly word an inner join - sql

Question

I am trying to learn joins and have read extensively here (SOFlow) and several other places and of course copied code and tried it out.
So I made this code to suit my table:
SELECT
a.FIRSTNAME, a.LASTNAME,
b.[LINE1], b.[LINE2], b.[LINE3], b.[SUBURB],
b.[STATE], b.[POSTCODE],
p.[PRIVATE], p.[BUSINESS], p.[MOBILE]
FROM
(SELECT
a.UNIQID, a.FIRSTNAME, a.LASTNAME
FROM [PTPARTY]) a
INNER JOIN
(SELECT
[LINE1], [LINE2], [LINE3], [SUBURB], [STATE], [POSTCODE], PARTYID
FROM
[PTAddresses]
WHERE
ADDRESS_TYPE = 'Mailing') b ON a.Uniqid = b.Partyid
INNER JOIN
(SELECT
[Uniqid], [PRIVATE], [BUSINESS], [MOBILE]
FROM [PTPhone]) P ON a.Uniqid = P.Uniqid
WHERE
a.UNIQID = 4
But I get:
Msg 4104, Level 16, State 1, Line 3
The multi-part identifier "a.UNIQID" could not be bound.
Msg 4104, Level 16, State 1, Line 3
The multi-part identifier "a.FIRSTNAME" could not be bound.
Msg 4104, Level 16, State 1, Line 3
The multi-part identifier "a.LASTNAME" could not be bound.
Where as this code perform perfectly
SELECT
a.FIRSTNAME, a.LASTNAME,
b.[LINE1], b.[LINE2], b.[LINE3], b.[SUBURB], b.[STATE], b.[POSTCODE],
p.[PRIVATE], p.[BUSINESS], p.[MOBILE]
FROM
(SELECT
PTPARTY.UNIQID, PTPARTY.FIRSTNAME, PTPARTY.LASTNAME
FROM [PTPARTY]) a
INNER JOIN
(SELECT
[LINE1], [LINE2], [LINE3], [SUBURB], [STATE], [POSTCODE], PARTYID
FROM
[PTAddresses]
WHERE
ADDRESS_TYPE = 'Mailing') b ON a.Uniqid = b.Partyid
INNER JOIN
(SELECT
[Uniqid], [PRIVATE], [BUSINESS], [MOBILE]
FROM [PTPhone]) P ON a.Uniqid = P.Uniqid
WHERE
a.UNIQID = 4
I am 99% sure the not Working code was copied from here with changes to fit my tables of course.
Just wondering if I am doing something wrong.
Well I am sure I am doing something wrong, but would like to know what.
Kind regards to you all and keep up the good work

Answer 1

You are qualifying the columns in the subquery but there is no corresponding table alias:
Select p.FIRSTNAME, p.LASTNAME, a.[LINE1],
a.[LINE2], a.[LINE3], a.[SUBURB], a.[STATE], a.[POSTCODE],
ph.[PRIVATE], ph.[BUSINESS], ph.[MOBILE]
from PTPARTY p inner join
PTAddresses a
on p.Uniqid = a.Partyid inner join
PTPhone ph
on p.Uniqid = Ph.Uniqid
where a.ADDRESS_TYPE = 'Mailing' and p.UNIQID = 4;
This is really much simpler.
Notice that I replaced the table alias with meaning aliases. However, you don't need the subqueries:

Answer 2

Check this Code. This will work. The error is due to first subquery as in first subquery you haven't aliased the table but used alias.column name. So change it to the following:
Select a.FIRSTNAME,a.LASTNAME, b.[LINE1],b.[LINE2],b.[LINE3],b.[SUBURB],b.[STATE],b.[POSTCODE],p.[PRIVATE],p.[BUSINESS],p.[MOBILE]
from
(SELECT UNIQID,FIRSTNAME,LASTNAME FROM [PTPARTY]) a
inner join
(SELECT [LINE1],[LINE2],[LINE3],[SUBURB],[STATE],[POSTCODE],PARTYID FROM [PTAddresses]
where ADDRESS_TYPE = 'Mailing') b on a.Uniqid = b.Partyid
inner join
(SELECT [Uniqid],[PRIVATE],[BUSINESS],[MOBILE]FROM [PTPhone]) P on a.Uniqid = P.Uniqid
where a.UNIQID = 4

Answer 3

To help be very specific:
Consider this part of your query:
FROM
(SELECT
a.UNIQID, a.FIRSTNAME, a.LASTNAME
FROM [PTPARTY]) a
When you remove the parenthesis from the subquery you have this:
SELECT
a.UNIQID, a.FIRSTNAME, a.LASTNAME
FROM [PTPARTY]
The item a.UNIQUID is in the form table alias.column name. However, inside the parentheses, you do not specify a table alias for [PTPARTY]. Thus, a.UNIQUID is invalid.
Since there is only 1 table, the alias or table reference is unnecessary. For clarity, I will add the optional "AS" from here on. With only 1 table, you can do this with only the column names:
FROM
(SELECT
UNIQID, FIRSTNAME, LASTNAME
FROM [PTPARTY]) AS a
Of course, you would often have joined tables and want to use aliases, so you can do that inside the parentheses:
FROM
(SELECT
z.UNIQID, z.FIRSTNAME, z.LASTNAME
FROM [PTPARTY] AS z) AS a
In this scenario, the table alias "z" is not available/valid outside of the parentheses. For that reason, even though it is probably not best practice, you can even re-use the same alias. Again, though, this can become confusing.
FROM
(SELECT
a.UNIQID, a.FIRSTNAME, a.LASTNAME
FROM [PTPARTY] AS a) AS a