Firebird 如何在带有子查询列的 ORDER BY 中使用 IIF

Question

以下查询不起作用，因为 Firebird (2.1) 无法识别子查询的列。我如何重写它才能工作？

SELECT I.InvoiceID,
  I.PayByDate,
  (SELECT FIRST 1 I2.PayByDate
  FROM Invoices I2
  WHERE I2.OriginalInvoiceID = I.InvoiceID
    AND I2.IsDraft < 1
  ORDER BY I2.InvoiceID DESC) AS NewPayByDate
FROM Invoices I
WHERE
  I.IsDraft < 1
ORDER BY
  IIF(NewPayByDate IS NULL,
    PayByDate,
    NewPayByDate),
  I.InvoiceRefNum

Answer 1

使用子查询：

SELECT InvoiceID, PayByDate, NewPayByDate
FROM (SELECT I.*
             (SELECT FIRST 1 I2.PayByDate
              FROM Invoices I2
              WHERE I2.OriginalInvoiceID = I.InvoiceID AND
                    I2.IsDraft < 1
              ORDER BY I2.InvoiceID DESC
             ) AS NewPayByDate
      FROM Invoices I
      WHERE I.IsDraft < 1
     ) I
ORDER BY IIF(NewPayByDate IS NULL, PayByDate, NewPayByDate),
         I.InvoiceRefNum;

我还建议在 ORDER BY:

中使用 COALESCE()

ORDER BY COALESCE(NewPayByDate, PayByDate),
         I.InvoiceRefNum;

Firebird 如何在带有子查询列的 ORDER BY 中使用 IIF

Firebird how to use IIF in ORDER BY with a subquery's column

sql

firebird

firebird2.1