Subquery in FROM cannot refer to other relations of same query level - sql

Question

I have 4 tables from which I want to select data based on some conditions: organisationunit,orgunitgroupmembers,orgunitgroup, orgunitgroupsetmember
and the select code:
SELECT *
FROM organisationunit,
orgunitgroupmembers,
orgunitgroup,
orgunitgroupsetmembers
WHERE organisationunit.comment = '1'
AND orgunitgroupmembers.organisationunitid = organisationunit.organisationunitid
AND orgunitgroup.orgunitgroupid = orgunitgroupmembers.orgunitgroupid
AND orgunitgroupsetmembers.orgunitgroupid = orgunitgroup.orgunitgroupid
AND orgunitgroupsetmembers.orgunitgroupsetid = '15633'
It does return what I want but now, I want to add these part
(select name
from organisationunit tt
where tt.organisationunitid =organisationunit.parentid) as rayon
after the select method:
SELECT *
FROM organisationunit,
orgunitgroupmembers,
orgunitgroup,
orgunitgroupsetmembers,
(SELECT NAME
FROM organisationunit tt
WHERE tt.organisationunitid = organisationunit.parentid) AS rayon
WHERE organisationunit.comment = '1'
AND orgunitgroupmembers.organisationunitid = organisationunit.organisationunitid
AND orgunitgroup.orgunitgroupid = orgunitgroupmembers.orgunitgroupid
AND orgunitgroupsetmembers.orgunitgroupid = orgunitgroup.orgunitgroupid
AND orgunitgroupsetmembers.orgunitgroupsetid = '15633'
and it gives the error
Subquery in FROM cannot refer to other relations of same query level
As you can see the table organisationunit has a parentid, which is a number and the same table organisationunit contains the name for that parentid. So I want at the end of the row in one column show the name of that parentid.
P.S I hope you got want I wanted, otherwise please feel free to ask the questions. Its first time that I do DB manipulations so far, if something is too obvious, believe me its NOT for me.

Answer 1

If am not wrong this is what you need. Here I made few changes.
Converted old style of join to proper INNER JOIN and moved the filters to where clause .
Next as mentioned in error you cannot refer the other tables in from clause of subquery. Actually you need to use correlated subquery to find the parent name or self join. or even a cross apply if it is supported
SELECT *,
(SELECT NAME
FROM organisationunit tt
WHERE tt.organisationunitid = organisationunit.parentid) AS rayon
FROM organisationunit
INNER JOIN orgunitgroupmembers
ON orgunitgroupmembers.organisationunitid = organisationunit.organisationunitid
INNER JOIN orgunitgroup
ON orgunitgroup.orgunitgroupid = orgunitgroupmembers.orgunitgroupid
INNER JOIN orgunitgroupsetmembers
ON orgunitgroupsetmembers.orgunitgroupid = orgunitgroup.orgunitgroupid
WHERE organisationunit.comment = '1'
AND orgunitgroupsetmembers.orgunitgroupsetid = '15633'
or even a self join to the same table to find the parent details.
SELECT *,
tt.NAME AS rayon
FROM organisationunit
INNER JOIN orgunitgroupmembers
ON orgunitgroupmembers.organisationunitid = organisationunit.organisationunitid
INNER JOIN orgunitgroup
ON orgunitgroup.orgunitgroupid = orgunitgroupmembers.orgunitgroupid
INNER JOIN orgunitgroupsetmembers
ON orgunitgroupsetmembers.orgunitgroupid = orgunitgroup.orgunitgroupid
INNER JOIN organisationunit tt
ON tt.organisationunitid = organisationunit.parentid
WHERE organisationunit.comment = '1'
AND orgunitgroupsetmembers.orgunitgroupsetid = '15633'

Answer 2

To get the name of the parent, use a self-join. Include one more reference to organisationunit in the from clause, with an alias tt or whatever. Something like this :
select A.*, B.*, C.*, D.*. tt.name as Rayon from organisationunit A,orgunitgroupmembers B,orgunitgroup C, orgunitgroupsetmembers D, organisationunit tt
where organisationunit.comment='1'
and orgunitgroupmembers.organisationunitid=organisationunit.organisationunitid
and orgunitgroup.orgunitgroupid =orgunitgroupmembers.orgunitgroupid
and orgunitgroupsetmembers.orgunitgroupid=orgunitgroup.orgunitgroupid
and orgunitgroupsetmembers.orgunitgroupsetid='15633'
and tt.organisationunitid =A.organisationunit.parentid
Of course, you may want to note that if the datasets are large, self-join may have some performance issues, in that case, you can use multi-step operation after selecting into temporary tables or whatever.