Oracle 11g Concat function error - sql

Question

I'm encountering this error:
ORA-00904: "LASTNAME": invalid identifier
When trying to make a report using concat function.
Here is the query:
SELECT 'Full Name','User Name', 'Email' FROM Dual
UNION ALL
SELECT distinct concat(concat(firstname, ' '), lastname), username, Email
FROM
(
select distinct concat(concat(firstname, ' '), lastname), username, Email
from sas_aclentry, sas_usergroup
where sas_aclentry.userkey = sas_usergroup.userkey
and objecttype in (16,3,4,101,14,102) and productkey = 1 and type = 1 and privilege !=0 and isdeleted = 0 and STATUS IN (0, 32)
UNION
select distinct concat(concat(firstname, ' '), lastname), username, Email
from sas_objecttree
join sas_usergroup on sas_usergroup.userkey = sas_objecttree.childkey
where isdeleted = 0 and STATUS IN (0, 32)
and parentkey in (
select distinct sas_aclentry.userkey
from sas_aclentry
join sas_usergroup on sas_usergroup.userkey = sas_aclentry.userkey
where objecttype in (16,3,4,101,14,102) and productkey = 1 and type = 2 and privilege !=0 and isdeleted = 0)
)
WHERE UPPER(Email) LIKE '%SAS%';
Wandered on google but could not find any way to make this works.
Please help.
Appreciate any input.
Will

Answer 1

The error seems to be that your outer query tries to select lastname from the derived table, which does not expose any column with that name. I'm guessing you meant to alias the concated column in the derived table and select that.
Try changing the beginning of the query to this:
SELECT 'Full Name','User Name', 'Email' FROM Dual
UNION ALL
SELECT fullname, username, Email
FROM
(
select distinct firstname || ' ' || lastname as fullname, username, Email
With some databases concat can take more than two arguments, I'm not sure this is true for Oracle though, but you should be able to use the concatenation operator || and change your nested concat functions to this:
firstname || ' ' || lastname as fullname
which makes the code a bit cleaner. (I would also try to be consistent in the use of explicit joins - in the derived table you use implicit joins for the first query and explicit for the second).

Answer 2

There are many mistakes in this query, besides what has already been pointed out (you are selecting "lastname" from a subquery whose projection does not contain a column by that name).
When you do a UNION, the first term of the union must have column names or aliases, which will be used for all the terms of the union. It does not suffice to select three strings from dual (which are probably meant to be used as headers), you must also give each of them an alias. For example, select 'Full Name' as fullname, ... from dual. Alternatively, you may leave the select... from dual for later in the union.
The fact that the "column headers" are shown at the top of the query does not mean they will be at the top of the result set. If you want them to show up at the top of your results, you must use an ORDER BY clause (which probably also means you will need to be able to order by something).
In the "problem" part of the Union, the select with a subquery, with the names and concatenations, you concatenate in the subquery, and then in the select list of the outer query you concatenate again (and supposedly the same three columns that the subquery concatenated already). This will not produce the result you wanted even if there were no syntax errors. What you probably want to do is to do the concatenation in the subquery (and best to use the || operator which may be used repeatedly, instead of concat() which is limited in Oracle); alias the result of the concatenation as fullname, and select fullname in the outer query.
After you fix these issues, others may come to the front; I (we) am/are not able to test, since you didn't provide any test inputs. Please follow up / write back if you need more help. Good luck!