SQL: Build dynamic query from list of tables received from user - sql

Question

I am attempting to build a dynamic query based on a list of tables as received from a user.
I have a couple attempted solutions below.
I think the CTE is the way to go but am having difficulty figuring out how to make it happen.
I would really appreciate whatever genius can let me know how to do this!
these are the tables:
W, WD, WE, WSF, WSFE, XDF, XDFE, Y, YD, Z, ZD
these are the columns to join by for each group of tables:
W, Y, WD, WE, WSF
WID
WSF, WSFE, XDF
WSFID
XDF, XDFE
XDFID
Y, YD, Z
YID
Z, ZD
ZID
if the user selects W, Y, Z then build this query (which could then be executed by exec or sp_executesql):
select * from #W w join #Y y on y.WID = w.WID join #Z z on z.YID = y.YID
declare #Fields table (
ID int identity not NULL,
Name varchar(200)
)
declare #Tables table (
ID int identity not NULL,
Field varchar(200),
TempTable varchar(200)
)
declare #QueryTables table (
ID int identity not NULL,
[Table] varchar(200),
Alias varchar(20)
)
declare #QueryJoins table (
ID int identity not NULL,
Table1 varchar(20),
Col1 varchar(200),
Table2 varchar(20),
Col2 varchar(200)
)
insert #Fields
values
('W'),
('Y'),
('Z')
insert #Tables
values
('W', '#W'),
('WD', '#WD'),
('WE', '#WE'),
('WSF', '#WSF'),
('WSFE', '#WSFE'),
('XDF', '#XDF'),
('XDFE', '#XDFE'),
('Y', '#Y'),
('YD', '#YD'),
('Z', '#Z'),
('ZD', '#ZD')
insert #QueryTables
values
('#W', 'w'),
('#WD', 'wd'),
('#WE', 'we'),
('#WSF', 'wsf'),
('#WSFE', 'wsfe'),
('#XDF', 'xdf'),
('#XDFE', 'xdfe'),
('#Y', 'y'),
('#YD', 'yd'),
('#Z', 'z'),
('#ZD', 'zd')
insert #QueryJoins
values
('w', 'WID', 'wd', 'WID'),
('w', 'WID', 'we', 'WID'),
('w', 'WID', 'wsf', 'WID'),
('w', 'WID', 'xdf', 'WID'),
('w', 'WID', 'y', 'WID'),
('wd', 'WID', 'w', 'WID'),
('we', 'WID', 'wd', 'WID'),
('wsf', 'WID', 'wd', 'WID'),
('wsf', 'WSFID', 'wsfe', 'WSFID'),
('wsfe', 'WSFID', 'wsf', 'WSFID'),
('wsf', 'WSFID', 'xdf', 'WSFID'),
('xdf', 'WID', 'w', 'WID'),
('xdf', 'WSFID', 'wsf', 'WSFID'),
('xdf', 'XDFID', 'xdfe', 'XDFID'),
('xdfe', 'XDFID', 'xdf', 'XDFID'),
('y', 'WID', 'w', 'WID'),
('y', 'YID', 'yd', 'YID'),
('yd', 'YID', 'y', 'YID'),
('y', 'YID', 'z', 'YID'),
('z', 'YID', 'y', 'YID'),
('z', 'ZID', 'zd', 'ZID'),
('zd', 'ZID', 'z', 'ZID')
--attempted solution number 1:
select
*
from #Fields vf
join #Tables vt
on vt.Field = vf.Name
join #QueryTables vqt
on vqt.[Table] = vt.TempTable
join #QueryJoins vqj
on vqj.Table1 = vqt.Alias
join #QueryTables vqt2
on vqt2.Alias = vqj.Table2
join #Tables vt2
on vt2.TempTable = vqt2.[Table]
join #Fields vf2
on vf2.Name = vt2.Field
--attempted solution number 2:
;with cte (FieldID, [Table], Table1, Col1, Table2, Col2, I) as (
select
vf.ID as FieldID,
vqt.[Table],
vqj.Table1,
vqj.Col1,
vqj.Table2,
vqj.Col2,
1
from #Fields vf
join #Tables vt
on vt.Field = vf.Name
join #QueryTables vqt
on vqt.[Table] = vt.TempTable
join #QueryJoins vqj
on vqj.Table1 = vqt.Alias
union all
select
vf.ID as FieldID,
vqt.[Table],
vqj.Table1,
vqj.Col1,
vqj.Table2,
vqj.Col2,
I + 1
from #Fields vf
join #Tables vt
on vt.Field = vf.Name
join #QueryTables vqt
on vqt.[Table] = vt.TempTable
join #QueryJoins vqj
on vqj.Table1 = vqt.Alias
join cte cte
on cte.Table1 = vqj.Table2
and cte.Table2 = vqj.Table1
where I <= FieldID --a feeble attempt to control the recursion
)
select * from cte

Answer 1

An interesting problem, definitely a data modeling code smell (if Z, Y, and YD all have a YID column, sounds like you need a bridge table or similar construct to manage the relationships there. Or if Z and YD are small lookups, just join them all and let the optimizer handle the overhead.)
Note: I made the fields self join on Name < Name, so you only need the QueryJoins data where Table1 < Table2. This would cut your QueryJoins table in half, but you're also missing some of the "correct" joins (ie you have we/wd but not wd/we)
declare #Fields table (
ID int identity not NULL,
Name varchar(200)
)
declare #Tables table (
ID int identity not NULL,
Field varchar(200),
TempTable varchar(200)
)
declare #QueryTables table (
ID int identity not NULL,
[Table] varchar(200),
Alias varchar(20)
)
declare #QueryJoins table (
ID int identity not NULL,
Table1 varchar(20),
Col1 varchar(200),
Table2 varchar(20),
Col2 varchar(200)
)
insert #Fields
values
('W'),
('Y'),
('Z')
insert #Tables
values
('W', '#W'),
('WD', '#WD'),
('WE', '#WE'),
('WSF', '#WSF'),
('WSFE', '#WSFE'),
('XDF', '#XDF'),
('XDFE', '#XDFE'),
('Y', '#Y'),
('YD', '#YD'),
('Z', '#Z'),
('ZD', '#ZD')
insert #QueryTables
values
('#W', 'w'),
('#WD', 'wd'),
('#WE', 'we'),
('#WSF', 'wsf'),
('#WSFE', 'wsfe'),
('#XDF', 'xdf'),
('#XDFE', 'xdfe'),
('#Y', 'y'),
('#YD', 'yd'),
('#Z', 'z'),
('#ZD', 'zd')
insert #QueryJoins
values
('w', 'WID', 'wd', 'WID'),
('w', 'WID', 'we', 'WID'),
('w', 'WID', 'wsf', 'WID'),
('w', 'WID', 'xdf', 'WID'),
('w', 'WID', 'y', 'WID'),
('wd', 'WID', 'w', 'WID'),
('we', 'WID', 'wd', 'WID'),
('wsf', 'WID', 'wd', 'WID'),
('wsf', 'WSFID', 'wsfe', 'WSFID'),
('wsfe', 'WSFID', 'wsf', 'WSFID'),
('wsf', 'WSFID', 'xdf', 'WSFID'),
('xdf', 'WID', 'w', 'WID'),
('xdf', 'WSFID', 'wsf', 'WSFID'),
('xdf', 'XDFID', 'xdfe', 'XDFID'),
('xdfe', 'XDFID', 'xdf', 'XDFID'),
('y', 'YID', 'yd', 'YID'),
('yd', 'YID', 'y', 'YID'),
('y', 'YID', 'z', 'YID'),
('z', 'ZID', 'zd', 'ZID'),
('zd', 'ZID', 'z', 'ZID')
;
with a as (
select
row_number() over (order by Name) as rn, Name, Field, TempTable, [Table], Alias
from #Fields vf
join #Tables vt
on vt.Field = vf.Name
join #QueryTables vqt
on vqt.[Table] = vt.TempTable )
select 'select * from ' + stuff((
select
concat(
case when a.rn =1 then a.TempTable else '' end,
' ',
case when a.rn =1 then a.Alias else '' end,
' join ',
a2.TempTable,
' ' ,
a2.alias,
' on ',
q.Table1,
'.',
q.Col1,
' = ',
q.Table2 ,
'.',
q.Col2 ) from a
left join a a2
on a.name < a2.name
inner join #QueryJoins q
on q.Table1 = a.alias
and q.Table2 = a2.alias
for xml path('')), 1, 1, '')