How to use an alias name in the current select

[Guy Deleeuw <G.De_Leeuw@xxxxxxxxxx>]

Hello

I have :
   SELECT
         t_orders_articles.k_id            AS k_id
        ,t_orders_articles.quantity        AS order_qty
        ,(SELECT sum(quantity) FROM t_deliveries_articles WHERE 
article_id = t_orders_articles.k_id) AS delivery_qty
        , (t_orders_articles.quantity - delivery_qty)       AS qty
      FROM t_orders_articles
       ......;

But it's not working I receive the error :
ERROR : The column delivery_qty does not exist.

How can I make that without having 2 select call ?

Regards
Guy


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