First CAST then concatenate (||) in Firebird - sql

Question

How does one cast and then join elements together in Firebird?
SELECT
ARTICLE_NAME ||','||CAST
FROM
(select cast(QUANTITY as varchar(50)) from PREORDER_ITEM)
I also tried
with DATA as ( select cast(QUANTITY as varchar(50) ) from PREORDER_ITEM )
SELECT
ARTICLE_NAME ||','||QUANTITY
FROM
DATA
Why doesn't this work?

Answer 1

There are multiple problems with your query:
When you do select cast(QUANTITY as varchar(50) ) from PREORDER_ITEM you have only one (1) column in the derived table. In other words, there is no ARTICLE_NAME in either query.
For a select expression of a derived table or common table expression, all columns must have an explicit column name. So, for an expression you need to specify an explicit alias using (AS <alias>). In other words, there is no column CAST in your first query, and no column QUANTITY in the second.
CAST is a reserved word, so when used as a column name like in your first query, it must be delimited by double quotes.
So, use:
select article_name || quantity
from (
select article_name, cast(quantity as varchar(50)) as quantity
from preorder_item
)
or
with data as (
select article_name, cast(quantity as varchar(50)) as quantity
from preorder_item
)
select article_name || quantity
from data
As an aside, you don't need to explicitly cast. When concatenating values, Firebird will automatically coerce to a string value, so you can also use:
select article_name || quantity
from preorder_item