SQL -- SELECT 3 TABLES WITH 2 IDs - sql

Question

I'm trying to join 3 tables where the two IDs from two tables are related but the third table is not related but the values are. It's very convoluted. I tried running a subquery without luck.
Here's the first table:
+---------------------------------+
| ListID | ListValue | ListLabel |
+--------------------------------+
| 1 | 1 | Male |
+--------------------------------+
Second table:
+--------------------+
| ListID | ListName |
+-------------------+
| 1 | Gender |
+-------------------+
Third table:
+---------------------------------+
| ClientID | Name | Gender |
+--------------------------------+
| 23422 | John West | 1 |
+--------------------------------+
So basically I'm looking for the Gender column from the third table to reference the first table where the ListValue column equals the Gender column. Yes, the Gender column value is stored as INT.
+---------------------------------+
| ClientID | Name | Gender |
+--------------------------------+
| 23422 | John West | Male |
+--------------------------------+

Answer 1

From a complete guess, the problem is your design, fix that, fix the problem. You should have 2 tables here, not 3. A Client table and a gender table, and then you can do a trivial JOIN:
CREATE TABLE dbo.Client (ClientID int NOT NULL,
[Name] nvarchar(50) NOT NULL,
Gender tinyint NULL); --As Gender is Sensitive data, and probably not mandatory as some don't wish to share
ALTER TABLE dbo.Client ADD CONSTRAINT PK_Client PRIMARY KEY CLUSTERED (ClientID);
GO
CREATE TABLE dbo.Gender (GenderID tinyint IDENTITY(1,1) NOT NULL,
GenderDescription varchar(15) NOT NULL);
ALTER TABLE dbo.Gender ADD CONSTRAINT PK_Gender PRIMARY KEY CLUSTERED (GenderID);
GO
ALTER TABLE dbo.Client ADD CONSTRAINT FK_ClientGender FOREIGN KEY (Gender) REFERENCES dbo.Gender (GenderID);
GO
--Assume existance of data
SELECT C.ClientID,
C.[Name],
G.GenderDescription AS Gender
FROM dbo.Client C
LEFT JOIN dbo.Gender G On C.Gender = G.GenderID; --LEFT JOIN as it's NULLable
GO
If you must stick with the design you have, you'll probably want to write it as subqueries; and it'll get messy pretty fast:
SELECT T3.ClientID,
T3.[Name],
(SELECT T1.ListLabel
FROM dbo.Table2 T2
JOIN dbo.Table1 T1 ON T2.ListID = T1.ListID
WHERE T2.ListName = N'Gender'
AND T1.ListValue = T3.Gender) AS Gender,
(SELECT T1.ListLabel
FROM dbo.Table2 T2
JOIN dbo.Table1 T1 ON T2.ListID = T1.ListID
WHERE T2.ListName = N'PrimaryLanguage'
AND T1.ListValue = T3.PrimaryLanguage) AS PrimaryLanguage
FROM dbo.Table3 T3;
You can put these (sub)queries in the FROM is you prefer using APPLY. I've used an OUTER rather than CROSS APPLY, as I assume that the value could be NULL and thus acts like a LEFT JOIN, rather than an INNER JOIN:
SELECT T3.ClientID,
T3.[Name],
G.Gender,
PL.PrimaryLanguage
FROM dbo.Table3 T3
OUTER APPLY (SELECT T1.ListLabel AS Gender
FROM dbo.Table2 T2
JOIN dbo.Table1 T1 ON T2.ListID = T1.ListID
WHERE T2.ListName = N'Gender'
AND T1.ListValue = T3.Gender) G
OUTER APPLY (SELECT T1.ListLabel AS PrimaryLanguage
FROM dbo.Table2 T2
JOIN dbo.Table1 T1 ON T2.ListID = T1.ListID
WHERE T2.ListName = N'PrimaryLanguage'
AND T1.ListValue = T3.Gender) PL;
To make it shorter, you could turn the "look up" part of the above into an inline table-value function, but I feel that entertaining that is validating the design, and I specifically don't want to do that.
This'll be a real pain to keep rewriting, but forced by the design choice. Though you could do this with Dynamic SQL, I doubt you'll be able to understand it or maintain it (as if you could understand dynamic SQL you'd have likely at least got the solution I give above), and I doubt you want to write all of your queries as a dynamic statement.
Fix the design, fix the problem (as I mentioned at the start).

Answer 2

This is a very bad data model. Change it if you can.
If there is a column gender in the client table, why muddle through with some generic list? Just add a table gender and link to its rows with client.gender_id:
table gender (gender_id, description)
table client (client_id, name, gender_id)
If you really must make this generic and are ready to live with the consequences (slower access, no guaranteed consistency, ...), then remove the gender column and add a table client_attribut instead, consisting of client_id, list_id and list_value.
Anyway, with your current design the query would be
select c.clientid, c.name, la.listlabel
from client c
join list_attribute la
on la.listvalue = c.gender
and la.listid = (select listid from list where listname = 'Gender')
order by c.clientid;

Answer 3

A simple join is of course possible, it's just unecessarily convoluted!
select t3.ClientId, t3.Name, t1.ListLabel as Gender
from t3 join t2 on t2.ListName='Gender'
join t1 on t1.ListId=t2.ListId and t2.ListValue=t3.Gender