如何计算两个别名的差异以进行排序

Question

考虑以下代码：

SELECT SUM(w.valor),
SUM(CASE WHEN w.tipo = '+' THEN w.valor ELSE 0 END) AS total_credit,
SUM(CASE WHEN w.tipo = '-' THEN w.valor ELSE 0 END) AS total_debit,
w.clientUNIQUE,
c.client as cclient
FROM wallet AS w
LEFT JOIN clients AS c ON w.clientUNIQUE = c.clientUNIQUE
WHERE w.status='V'
GROUP BY w.clientUNIQUE
ORDER BY total_credit-total_debit

我正在尝试计算两个别名计算值的差值以进行排序，但出现以下错误：

Reference 'total_credit' not supported (reference to group function)

我哪里做错了，如何使用两个别名之间的差值对结果进行排序？

Answer 1

您不能在同一 select 表达式中通过别名引用列，因此有 2 个选项...

重复 order by 中的表达式（yuk）：

ORDER BY
  SUM(CASE WHEN w.tipo = '+' THEN w.valor ELSE 0 END) AS total_credit -
  SUM(CASE WHEN w.tipo = '-' THEN w.valor ELSE 0 END) AS total_debit

或者更容易大脑和更容易维护（DRY），通过子查询订购：

select * from (
  <your query without the ORDER BY>
) q
ORDER BY total_credit - total_debit

如何计算两个别名的差异以进行排序

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