SQL SELECT from and EAV table - sql

Question

Based on my previous questions I have this following tables:
IrisColor
ID Description
1 Blue
2 Gray
3 Green
4 Brown
SkinColor
ID Description
1 White
2 Asian
3 Dark
Gender
ID Description
1 Male
2 Female
And the Attributes table
Attributes
ID Description
1 SkinColor
2 IrisColor
3 Gender
And also the EAV table:
PersonDetails
PersonID AttributeID ValueID
121 1 1
121 2 2
121 3 1
122 1 2
122 2 1
122 3 1
So if I would want to select the Name, the attribute name and value for only the SkinColor I would do something like this:
SELECT p.Name,
a.Description,
v.Description
FROM PersonDetails AS sd
INNER JOIN Subjects AS p ON sd.PersonID=p.ID
INNER JOIN SubjectAttributes AS a ON sd.AttributeID=a.ID
INNER JOIN SkinColor AS v ON sd.ValueID= v.ID
But what should I do If I would want to select all the information for all of the persons from the database, not only skin color but iris color and gender too?
Previously I knew that from SkinColor I wanted to select that value, but in the PersonDetails I also have Values for IrisColor and Gender.
INNER JOIN SkinColor AS v ON sd.ValueID= v.ID this won't be appropriate anymore. How to replace this with something more dynamical?
Update:
I used this statement:
SELECT
SubjectID,
SkinColor,
IrisColor,
EyeLidFlisure,
KnownEyeDeffect,
Ethnicity,
Height,
DrivingLicense,
Gender
FROM
(
SELECT SubjectID, attr.Description as attribute, ValueID from SubjectDetails, SubjectAttributes as attr WHERE SubjectDetails.AttributeID=attr.ID
) as t
PIVOT(MAX(ValueID) FOR attribute IN (SkinColor,IrisColor,Gender,EyeLidFlisure,KnownEyeDeffect,Ethnicity,Height,DrivingLicense)) AS t1
Now, I have all the attributes listed in separate columns, but instead of Value description I have Value ID. How should I continue?

Answer 1

Guess you need dynamic sql built from attributes dictionary
declare #sql varchar(max)=
'select PersonID , ' +
+ stuff((select ','+Description + '.Description as ' + Description
from Attributes
for xml path ('')),1,1,'')
+ ' from (select PersonID, '
+ stuff((select ',max(case AttributeID when ' + cast(ID as varchar(5)) +' then ValueID end) as ' + Description
from Attributes
for xml path ('')),1,1,'')
+' from PersonDetails group by PersonID ) pvt'
+ (select ' left join ' + Description + ' on pvt.' + Description + ' = '+ Description + '.ID'
from Attributes
for xml path (''));
exec (#sql);

Answer 2

Your data model is a bit arcane, because you have ids in the "person details" table that cannot have proper foreign key relationships. You could put all the attributes in the same table. Or have a separate table for each attribute. Or -- as is common with EAV models -- put the descriptions directly into PersonDetails.
You are going to need to do something like this:
SELECT p.Name,
sa.Description,
ic.Description as IrisColor,
g.Description as gender
FROM PersonDetails sd INNER JOIN
Subjects p
ON sd.PersonID = p.ID INNER JOIN
SubjectAttributes sa
ON sd.AttributeID = sa.ID
ON LEFT JOIN
SkinColor sc
ON sd.ValueID = sc.ID AND sa.Description = 'SkinColor' LEFT JOIN
IrisColor ic
ON sd.ValueId = ic.ID AND sa.Description = 'IrisColor' LEFT JOIN
Gender g
ON sd.ValueId = g.ID AND sa.Description = 'Gender';

Answer 3

This would be the complete solution (don't know if it is the easiest one.. but it works)
WITH Subject AS (
SELECT
SubjectID,
SkinColor,
IrisColor,
EyeLidFlisure,
KnownEyeDeffect,
Ethnicity,
Height,
DrivingLicense,
Gender
FROM
(
SELECT SubjectID, attr.Description as attribute, ValueID from SubjectDetails, SubjectAttributes as attr WHERE SubjectDetails.AttributeID=attr.ID
) as t
PIVOT(MAX(ValueID) FOR attribute IN (SkinColor,IrisColor,Gender,EyeLidFlisure,KnownEyeDeffect,Ethnicity,Height,DrivingLicense)) AS t1
)
SELECT SubjectID,
whole.Name as Name,
whole.eMail as eMail,
skincolor.Description as SkinColor,
iriscolor.Description as IrisColor,
eyelid.Description as EyeLidFlisure,
defect.Description as KnownEyeDeffect,
eth.Description as Ethnicity,
height.Description as Height,
dl.Description as DrivingLicense,
gender.Description as Gender
FROM Subject S
Left JOIN Subjects whole ON whole.ID=S.SubjectID
Left JOIN SkinColor skincolor ON S.SkinColor=skincolor.ID
Left JOIN IrisColor iriscolor ON S.IrisColor=iriscolor.ID
Left JOIN EyeLidFlisure eyelid ON S.EyeLidFlisure=eyelid.ID
Left JOIN KnownEyeDeffect defect ON S.KnownEyeDeffect=defect.ID
Left JOIN Ethnicity eth ON S.Ethnicity=eth.ID
Left JOIN Height height ON S.Height=height.ID
Left JOIN DrivingLicense dl ON S.DrivingLicense=dl.ID
Left JOIN Gender gender ON S.Gender=gender.ID