Dynamically Join Enum Table with other Table - sql

Question

I have the following table. These are not the real tables but the concept is here.
Table1
----------------------------------
FieldID|EnumeratedValue|TextValue
----------------------------------
Col1 |1 |Hey
----------------------------------
Col1 |2 |Test
----------------------------------
Col1 |3 |George
----------------------------------
Col2 |1 |Random
----------------------------------
Col2 |2 |Wesley
----------------------------------
Col3 |1 |Tompson
----------------------------------
Col3 |2 |Oooo
----------------------------------
Table2
----------------------------------
Col1 |Col2 |Col3
----------------------------------
1 |2 |1
----------------------------------
2 |1 |1
----------------------------------
3 |1 |2
----------------------------------
The desired result would be a view
----------------------------------
Col1 |Col2 |Col3
----------------------------------
Hey |Wesley |Tompson
----------------------------------
Test |Random |Tompson
----------------------------------
George |Random |Oooo
----------------------------------
So you could write something like
SELECT col1.TextValue,col2.TextValue,col3.TextValue
FROM Table2 t2,
(SELECT * FROM Table1 WHERE FieldID = 'Col1') col1,
(SELECT * FROM Table1 WHERE FieldID = 'Col2') col2,
(SELECT * FROM Table1 WHERE FieldID = 'Col3') col3
WHERE t2.col1 = col1.EnumeratedValue and t2.col2 = col2.EnumeratedValue and t2.col3 = col3.EnumeratedValue
The problem is that in our real tables there ~20 of these columns per table. I would like to find a simpler means of writing this code. I do not want to hard code 20 joins for each view that I am making. Let me know if there are any alternatives.

Answer 1

As with any variable join solution, a dynamic pivot is really the better way to look at this. It's not as performance as a hard-coded, non-pivot solution, but this will involve the least development hours, and can be adapted to generate view definitions rather than made into a table-valued function (which could be fed a table name and possibly column names to pivot and join)
First, the demo data setup:
if object_id('dbo.test_enum') is not null drop table dbo.test_enum
create table dbo.test_enum (
FieldID sysname
, EnumeratedValue int not null
, TextValue sysname
, primary key (FieldID, EnumeratedValue)
)
INSERT INTO dbo.test_enum
(FieldID, EnumeratedValue, TextValue)
VALUES
('Col1', 1, 'Hey'),
('Col1', 2, 'Test'),
('Col1', 3, 'George'),
('Col2', 1, 'Random'),
('Col2', 2, 'Wesley'),
('Col3', 1, 'Tompson'),
('Col3', 2, 'Oooo')
;
if object_id('dbo.test_table') is not null drop table dbo.test_table
create table test_table (
id int primary key identity(1,1)
, Col1 int not null
, Col2 int not null
, Col3 int not null
);
INSERT INTO dbo.test_table
(Col1, Col2, Col3)
VALUES
(1,2,1),
(2,1,1),
(3,1,2)
Next is the dynamic selection part:
declare #cols nvarchar(max) = (select stuff((
select ',' + quotename(c.name)
from sys.objects o
inner join sys.columns c on c.object_id = o.object_id
where o.name = 'test_table'
and c.name in ('Col1', 'Col2', 'Col3')
for xml path ('')
),1,1,''))
declare #SQL nvarchar(max) = N'
select p.id, ' + #cols + '
from (
select unp.id, unp.FieldID, e.TextValue
from dbo.test_table
unpivot (
EnumeratedValues FOR FieldID IN (' + #cols + ')
) unp
inner join dbo.test_enum e on e.EnumeratedValue = unp.EnumeratedValues
and e.FieldID = unp.FieldID
) z
pivot (
min(z.TextValue) FOR z.FieldID IN (' + #cols + ')
) p
'
exec sp_executesql #sql
On its own, this will return the result set desired in the question, but can be adapted to return view definitions of any given table/column data set, and then further adapted per table/view.