mytable.lhs

> {-# LANGUAGE TemplateHaskell, MultiParamTypeClasses, FlexibleInstances #-}
>
> import Data.Int
>
> import Database.Relational.Query
> import Database.Relational.Query.TH
>
>
> $(defineTableDefault defaultConfig
>   "PUBLIC" "my_table"
>   [ ("person", [t| String |])
>   , ("family", [t| String |])
>   , ("age"   , [t| Int32 |])
>   ]
>   [] [0] (Just 0))
>
>
> agesOfFamiliesQ :: QueryAggregate (Projection Aggregated (String, Maybe Int32))
> agesOfFamiliesQ =  do
>   my <- query myTable
>   gFam <- groupBy $ my ! family'
>   return $ gFam >< sum' (my ! age')
>
> justAgeOfFamilies0 :: Relation () (Maybe Int32)
> justAgeOfFamilies0 =  aggregateRelation $ do
>   pair <- agesOfFamiliesQ
>   return $ pair ! snd'
>
> -- *Main> justAgeOfFamilies0
> -- SELECT ALL SUM (T0.age) AS f0 FROM PUBLIC.my_table T0 GROUP BY T0.family
>
> agesOfFamilies :: Relation () (String, Maybe Int32)
> agesOfFamilies =  aggregateRelation agesOfFamiliesQ
>
> justAgeOfFamilies1 :: Relation () (Maybe Int32)
> justAgeOfFamilies1 =  relation $ do
>   pair <- query agesOfFamilies
>   return $ pair ! snd'
>
> -- *Main> justAgeOfFamilies1
> -- SELECT ALL T1.f1 AS f0
> --   FROM (SELECT ALL T0.family AS f0, SUM (T0.age) AS f1
> --           FROM PUBLIC.my_table T0 GROUP BY T0.family) T1
>
> main :: IO ()
> main =  do
>   putStrLn "0"
>   print justAgeOfFamilies0
>   putStrLn "1"
>   print justAgeOfFamilies1