SQL join and Bring in 1 column into 2 columns - sql

Question

I have two tables shown as above. I want to create a select statement that would have the following result:
Basically, I want to join on 'Model' and 'Num' columns and bring 'Val' vales but break it into two columns based on 'Ver'.
SELECT 'a' as Model ,'1' as Num ,'v1' as Ver ,'9' as val INTO #RefTbl UNION ALL
SELECT 'a','2','v1','10' UNION ALL
SELECT 'a','3','v1','11' UNION ALL
SELECT 'a','1','v2','5' UNION ALL
SELECT 'a','2','v2','6' UNION ALL
SELECT 'a','3','v2','7' UNION ALL
SELECT 'b','1','v1','20' UNION ALL
SELECT 'b','1','v2','21' UNION ALL
SELECT 'b','2','v1','25' UNION ALL
SELECT 'b','2','v2','26'
SELECT '519' as ID,'a' as Model,'1' as Num INTO #OrderTbl UNION ALL
SELECT '5616','a','3' UNION ALL
SELECT '871','b','1'
-- failed attempt
SELECT o.*, '' as v1_val, '' as v2_val FROM #OrderTbl as o left join #RefTbl as r on o.Model = r.Model and o.Num = r.Num

Answer 1

You can join and do conditional aggregation:
select
d.ID,
d.Model,
d.Num,
max(case when r.Ver = 'val1' then Val end) V1_Val,
max(case when r.Ver = 'val2' then Val end) V2_Val
from DataTbl d
inner join ReferenceTbl r
on r.Model = d.Model
and r.Num = d.Num
group by
d.ID,
d.Model,
d.Num
Alternatively, you can join twice - depending on your dataset, this might (or might not) perform better:
select
d.ID,
d.Model,
d.Num,
r1.Val V1_Val,
r2.Val V2_Val
from DataTbl d
left join ReferenceTbl r1
on r1.Model = d.Model
and r1.Num = d.Num
and r1.Ver = 'val1'
left join ReferenceTbl r2
on r2.Model = d.Model
and r2.Num = d.Num
and r2.Ver = 'val2'

Answer 2

Case + Group by works on most db system which is nice.
Alternative answer using SQL Server PIVOT (for reference)
WITH RefTbl AS (
SELECT 'a' as Model ,'1' as Num ,'v1' as Ver ,'9' as val UNION ALL
SELECT 'a','2','v1','10' UNION ALL
SELECT 'a','3','v1','11' UNION ALL
SELECT 'a','1','v2','5' UNION ALL
SELECT 'a','2','v2','6' UNION ALL
SELECT 'a','3','v2','7' UNION ALL
SELECT 'b','1','v1','20' UNION ALL
SELECT 'b','1','v2','21' UNION ALL
SELECT 'b','2','v1','25' UNION ALL
SELECT 'b','2','v2','26'),
OrderTbl AS (
SELECT '519' as ID,'a' as Model,'1' as Num UNION ALL
SELECT '5616','a','3' UNION ALL
SELECT '871','b','1'
)
SELECT Id, Model, Num AS Model, [v1] AS v1_Val, [v2] as v2_Val
FROM
(SELECT o.id, r.Model, r.Num, r.val, r.ver from OrderTbl as o
left join RefTbl as r on o.Model = r.Model and o.Num = r.Num) AS SourceTable
PIVOT
(MAX(val) FOR ver IN ([v1], [v2])) AS PivotTable;
Id Model Model v1_Val v2_Val
519 a 1 9 5
5616 a 3 11 7
871 b 1 20 21