一次通话中多个日期范围的总和？

Question

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');

这样做会增加这两个日期之间发生的所有"费用".大.工作良好.

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

但有没有办法将其压缩为所有日期范围的单个查询？

例如,我要求SUM一系列这样的范围:

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

我需要输出在每个日期范围内收集的费用总和(最终需要在数组中).

那么,关于处理和减少数据库事务的方法的任何想法？

FWIW,这是在Rails应用程序内的Postgres上.

Answer 1

假设我正确理解了您的要求,我认为您需要的是这样的:

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句点.由于查询是在前端即时"生成"的,因此您可以根据需要向句点部分添加任意数量的行.

编辑:通过一些试验和错误,我设法使其工作[在sqlFiddle] [1]并相应地更新上面的语法.