追加しようと思うexample

exmaples.hs

account1'' :: Relation () Account1
account1'' = relation $ do
  a  <- query account
  wheres $ a ! Account.productCd' `in'` values ["CHK", "SAV", "CD", "MM"]
  return $ Account1 |$| a ! Account.accountId'
                    |*| a ! Account.productCd'
                    |*| a ! Account.custId'
                    |*| a ! Account.availBalance'

data Account1 = Account1
  { a1AccountId :: Int64
  , a1ProductCd :: String
  , a1CustId :: Int64
  , a1AvailBalance :: Maybe Double
  } deriving (Show)

$(makeRecordPersistableDefault ''Account1)

-- | sql/4.3.3b.sh
--
-- @
--   SELECT account_id, product_cd, cust_id, avail_balance
--   FROM account
--   WHERE product_cd IN (SELECT product_cd FROM product
--   WHERE product_type_cd = 'ACCOUNT')
-- @

productSubQuery :: Relation String String
productSubQuery = relation' $ do
  p <- query product
  (phProductCd,()) <- placeholder (\ph -> wheres $ p ! Product.productTypeCd' .=. ph)
  let productCd = p ! Product.productCd'
  return (phProductCd, productCd)

account1b :: Relation String Account
account1b = relation' $ do
  a <- query account
  (phProductCd,p) <- queryList' productSubQuery
  wheres $ a ! Account.productCd' `in'` p
  return (phProductCd, a)

account1b' :: Relation String (((Int64, String), Int64), Maybe Double)
account1b' = undefined

account1b'' :: Relation String Account
account1b'' = undefined