Opaleye.Order

Documentation

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)

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 :: 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.

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

data Order a

An Order represents an expression to order on and a sort direction. Multiple Orders can be composed with mappend. If two rows are equal according to the first Order, the second is used, and so on.

Instances

Divisible Order

Decidable Order

Contravariant Order

Monoid (Order a)

Semigroup (Order a)