Error in select statement, with union all in a subquery - sql

Question

In Oracle 11g, I came across an error for a query and cannot figure why it is erroring on me. Here is the query:
select
main_data.issue_number,
main_data.transaction_number
from
(
select
p1.payment_date,
p1.media_number,
p1.payment_amount,
p1.issue_number,
p1.advice_na_number,
name.name_address_line_1,
name.name_address_line_2,
name.name_address_line_3,
name.name_address_line_4,
name.name_address_line_5,
name.name_address_line_6,
name.name_address_line_7,
name.name_address_city,
name.state_code,
name.address_country_code,
name.zip_code,
name.tax_id_number,
p1.output_tx_number_prin,
p1.output_tx_number_int,
'' as "transaction_number",
p1header.check_account_number
from
p1
left join name on p1.name_address_number = name.name_address_number
left join p1header on p1.issue_number = p1header.issue_number
UNION ALL
select
check.date_of_payment,
check.media_number,
check.payment_amount,
check.issue_number,
check.payee_na_number,
name.name_address_line_1,
name.name_address_line_2,
name.name_address_line_3,
name.name_address_line_4,
name.name_address_line_5,
name.name_address_line_6,
name.name_address_line_7,
name.name_address_city,
name.state_code,
name.address_country_code,
name.zip_code,
name.tax_id_number,
'' as "output_tx_number_prin",
'' as "output_tx_number_int",
check.transaction_number,
check.dda_number as "check_account_number"
from check
left join name on check.payee_na_number = name.name_address_number
) main_data
Selecting individual fields like above will give me an "invalid identifier error". If I do select * then it gives me back the data without any error. What am I doing wrong here? Thank you.

Answer 1

The old quoted identifier problem... see point 9 in the database object naming documentation, and note that Oracle does not recommend using quoted identifiers.
You've put your column alias as lower case inside double-quotes. That means that any references to it also have to be quoted and exactly match the case. So this would work:
select
main_data.issue_number,
main_data."transaction_number"
from
...
But unless you have a burning need to have that alias like that - and I doubt you do as all the identifier names from the actual table columns are not quoted - it would be simpler to remove the double quotes from the inner selects:
select
main_data.issue_number,
main_data.transaction_number
from
(
select
...
'' as transaction_number,
p1header.check_account_number
...
UNION ALL
select
...
'' as output_tx_number_prin,
'' as output_tx_number_int,
check.transaction_number,
check.dda_number as check_account_number
...
You don't actually need to alias the columns in the second branch of the union; the column identifiers will all be taken from the first branch.