Opaleye.Order

Ordering, LIMIT and OFFSET

Order by

orderBy :: Order a -> Query a -> Query a

Order the rows of a Query according to the Order.

import Data.Monoid ((<>))

-- Order by the first column ascending.  When first columns are equal
-- order by second column descending.
example :: Query (Column PGInt4, Column PGText)
        -> Query (Column PGInt4, Column PGText)
example = orderBy (asc fst <> desc snd)

data Order a

An Order a represents a sort order and direction for the elements of the type a. Multiple Orders can be composed with mappend or (<>) from Data.Monoid. If two rows are equal according to the first Order in the mappend, the second is used, and so on.

Instances

Divisible Order

Methods

divide :: (a -> (b, c)) -> Order b -> Order c -> Order a

conquer :: Order a

Decidable Order

Methods

lose :: (a -> Void) -> Order a

choose :: (a -> Either b c) -> Order b -> Order c -> Order a

Contravariant Order

Methods

contramap :: (a -> b) -> Order b -> Order a

(>$) :: b -> Order b -> Order a

Semigroup (Order a)

Methods

(<>) :: Order a -> Order a -> Order a

sconcat :: NonEmpty (Order a) -> Order a

stimes :: Integral b => b -> Order a -> Order a

Monoid (Order a)

Methods

mempty :: Order a

mappend :: Order a -> Order a -> Order a

mconcat :: [Order a] -> Order a

Order direction

asc :: PGOrd b => (a -> Column b) -> Order a

Specify an ascending ordering by the given expression. (Any NULLs appear last)

desc :: PGOrd b => (a -> Column b) -> Order a

Specify an descending ordering by the given expression. (Any NULLs appear first)

ascNullsFirst :: PGOrd b => (a -> Column b) -> Order a

Specify an ascending ordering by the given expression. (Any NULLs appear first)

descNullsLast :: PGOrd b => (a -> Column b) -> Order a

Specify an descending ordering by the given expression. (Any NULLs appear last)

Limit and offset

limit :: Int -> Query a -> Query a

Limit the results of the given query to the given maximum number of items.

offset :: Int -> Query a -> Query a

Offset the results of the given query by the given amount, skipping that many result rows.

Other

class PGOrd a

Typeclass for Postgres types which support ordering operations.

Instances

PGOrd PGCitext

PGOrd PGUuid

PGOrd PGTimestamptz

PGOrd PGTimestamp

PGOrd PGTime

PGOrd PGText

PGOrd PGNumeric

PGOrd PGInt2

PGOrd PGInt4

PGOrd PGInt8

PGOrd PGFloat8

PGOrd PGFloat4

PGOrd PGDate

PGOrd PGBool

PGOrd a => PGOrd (Nullable a)