单个查询中多个日期范围的总和？

我有以下查询：

SELECT 
   SUM("balance_transactions"."fee") AS sum_id 
   FROM "balance_transactions" 
   JOIN charges ON balance_transactions.source = charges.balance_id 
   WHERE "balance_transactions"."account_id" = 6 
      AND (balance_transactions.type = 'charge' 
      AND charges.refunded = false 
      AND charges.invoice IS NOT NULL) 
      AND ("balance_transactions"."created" BETWEEN '2013-12-20' AND '2014-01-19');

其作用是将这两个日期之间发生的所有“费用”相加。伟大的。工作正常。

问题是我几乎总是一次需要数百个日期范围的这些费用，这相当于我运行相同的查询数百次。效率不高。

但是有什么方法可以将其压缩为所有日期范围的单个查询吗？

例如，我会打电话SUM对于这样的一系列范围：

2013-12-20 to 2014-01-19
2013-12-21 to 2014-01-20
2013-12-22 to 2014-01-21
2013-12-23 to 2014-01-22
2013-12-24 to 2014-01-23
...so on and so on

我需要输出每个日期范围内收取的费用总和（最终需要将其放入数组中）。

那么，有什么办法可以处理这个问题并减少数据库事务吗？

FWIW，这是在 Rails 应用程序内的 Postgres 上。

假设我正确理解您的请求，我认为您需要的是以下内容：

SELECT "periods"."start_date", 
       "periods"."end_date", 
       SUM(CASE WHEN "balance_transactions"."created" BETWEEN "periods"."start_date" AND "periods"."end_date" THEN "balance_transactions"."fee" ELSE 0.00 END) AS period_sum
  FROM "balance_transactions" 
  JOIN charges ON balance_transactions.source = charges.balance_id 
  JOIN ( SELECT '2013-12-20'::date as start_date, '2014-01-19'::date as end_date UNION ALL
         SELECT '2013-12-21'::date as start_date, '2014-01-20'::date as end_date UNION ALL
         SELECT '2013-12-22'::date as start_date, '2014-01-21'::date as end_date UNION ALL
         SELECT '2013-12-23'::date as start_date, '2014-01-22'::date as end_date UNION ALL
         SELECT '2013-12-24'::date as start_date, '2014-01-23'::date as end_date
         ) as periods
    ON "balance_transactions"."created" BETWEEN "periods"."start_date" AND "periods"."end_date"
 WHERE "balance_transactions"."account_id" = 6 
   AND "balance_transactions"."type" = 'charge' 
   AND "charges"."refunded" = false 
   AND "charges"."invoice" IS NOT NULL
 GROUP BY "periods"."start_date", "periods"."end_date"

这应该会在一个结果集中返回您感兴趣的所有期间。 由于查询是在前端动态“生成”的，因此您可以根据需要向周期部分添加任意多的行。

编辑：经过一些试验和错误，我设法让它工作 [in sqlFiddle][1] 并相应地更新了上面的语法。