src/Rel8/Table/Window.hs · rel8

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rel8/src/Rel8/Table/Window.hs

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1{-# language MonoLocalBinds #-}

3module Rel8.Table.Window

4 ( cumulative

5 , cumulative_

6 , currentRow

7 )

8where

10-- base

11import Prelude

13-- opaleye

14import qualified Opaleye.Window as Opaleye

16-- rel8

17import Rel8.Aggregate ( Aggregates )

18import qualified Rel8.Expr.Window as Expr

19import Rel8.Schema.HTable ( hfield, htabulateA )

20import Rel8.Table ( fromColumns, toColumns )

21import Rel8.Window ( Window( Window ) )

24-- | 'cumulative' allows the use of aggregation functions in 'Window'

25-- expressions. In particular, @'cumulative' 'Rel8.sum'@

26-- (when combined with 'Rel8.Window.orderPartitionBy') gives a running total,

27-- also known as a \"cumulative sum\", hence the name @cumulative@.

28cumulative :: Aggregates aggregates exprs => (a -> aggregates) -> Window a exprs

29cumulative f =

30 fmap fromColumns $

31 htabulateA $ \field ->

32 Expr.cumulative ((`hfield` field) . toColumns . f)

35-- | A version of 'cumulative' for use with nullary aggregators like

36-- 'Rel8.Expr.Aggregate.countStar'.

37cumulative_ :: Aggregates aggregates exprs => aggregates -> Window a exprs

38cumulative_ = cumulative . const

41-- | Return every column of the current row of a window query.

42currentRow :: Window a a

43currentRow = Window $ Opaleye.over (Opaleye.noWindowFunction id) mempty mempty