Complex query in QSqlQuery

[wysota]

Just a side note - I'd use a different query (it may be invalid but I mean the general idea):

SELECT
          MAX(cardid)+1 AS 'id',
          t.date,
          o.name,
          t.amount
      FROM `transactions` AS t
      INNER JOIN `operations` AS o ON t.operation=o.id
      WHERE
          operation>=1000 && operation<2000 GROUP BY cardid
      ORDER BY date;

SELECT
          MAX(cardid)+1 AS 'id',
          t.date,
          o.name,
          t.amount
      FROM `transactions` AS t
      INNER JOIN `operations` AS o ON t.operation=o.id
      WHERE
          operation>=1000 && operation<2000 GROUP BY cardid
      ORDER BY date;

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MAX is safer than COUNT.

But honestly that's a perfect usecase for triggers - you can have a trigger that will calculate the id itself and modify the query on the fly.