diff --git a/changelog.d/20231009_170616_shane.obrien_mode.md b/changelog.d/20231009_170616_shane.obrien_mode.md
new file mode 100644
index 00000000..158dea7b
--- /dev/null
+++ b/changelog.d/20231009_170616_shane.obrien_mode.md
@@ -0,0 +1,3 @@
+### Added
+
+- Add support for ordered-set aggregation functions, including `mode`, `percentile`, `percentileContinuous`, `hypotheticalRank`, `hypotheticalDenseRank`, `hypotheticalPercentRank` and `hypotheticalCumeDist`.
diff --git a/src/Rel8.hs b/src/Rel8.hs
index 38cd1f3a..722ffa07 100644
--- a/src/Rel8.hs
+++ b/src/Rel8.hs
@@ -272,7 +272,6 @@ module Rel8
   , groupBy, groupByOn
   , listAgg, listAggOn, listAggExpr, listAggExprOn
   , listCat, listCatOn, listCatExpr, listCatExprOn
-  , mode
   , nonEmptyAgg, nonEmptyAggOn, nonEmptyAggExpr, nonEmptyAggExprOn
   , nonEmptyCat, nonEmptyCatOn, nonEmptyCatExpr, nonEmptyCatExprOn
   , DBMax, max, maxOn
@@ -286,6 +285,14 @@ module Rel8
   , and, andOn
   , or, orOn
 
+  , mode, modeOn
+  , percentile, percentileOn
+  , percentileContinuous, percentileContinuousOn
+  , hypotheticalRank
+  , hypotheticalDenseRank
+  , hypotheticalPercentRank
+  , hypotheticalCumeDist
+
     -- ** Ordering
   , orderBy
   , Order
diff --git a/src/Rel8/Expr/Aggregate.hs b/src/Rel8/Expr/Aggregate.hs
index a9aaeeaf..849cb12c 100644
--- a/src/Rel8/Expr/Aggregate.hs
+++ b/src/Rel8/Expr/Aggregate.hs
@@ -4,6 +4,7 @@
 {-# language NamedFieldPuns #-}
 {-# language OverloadedStrings #-}
 {-# language ScopedTypeVariables #-}
+{-# language TypeApplications #-}
 {-# language TypeFamilies #-}
 
 {-# options_ghc -fno-warn-redundant-constraints #-}
@@ -17,6 +18,13 @@ module Rel8.Expr.Aggregate
   , sum, sumOn, sumWhere
   , avg, avgOn
   , stringAgg, stringAggOn
+  , mode, modeOn
+  , percentile, percentileOn
+  , percentileContinuous, percentileContinuousOn
+  , hypotheticalRank
+  , hypotheticalDenseRank
+  , hypotheticalPercentRank
+  , hypotheticalCumeDist
   , groupByExpr, groupByExprOn
   , distinctAggregate
   , filterWhereExplicit
@@ -28,6 +36,7 @@ module Rel8.Expr.Aggregate
 where
 
 -- base
+import Data.Functor.Contravariant ((>$<))
 import Data.Int ( Int64 )
 import Data.List.NonEmpty ( NonEmpty )
 import Data.String (IsString)
@@ -36,6 +45,7 @@ import Prelude hiding (and, max, min, null, or, show, sum)
 -- opaleye
 import qualified Opaleye.Aggregate as Opaleye
 import qualified Opaleye.Internal.Aggregate as Opaleye
+import qualified Opaleye.Internal.HaskellDB.PrimQuery as Opaleye
 import qualified Opaleye.Internal.Operators as Opaleye
 
 -- profunctors
@@ -59,17 +69,22 @@ import Rel8.Expr.Opaleye
   , fromPrimExpr
   , toColumn
   , toPrimExpr
+  , unsafeCastExpr
   )
+import Rel8.Expr.Order (asc)
 import Rel8.Expr.Read (sread)
 import Rel8.Expr.Show (show)
 import qualified Rel8.Expr.Text as Text
+import Rel8.Order (Order (Order))
 import Rel8.Schema.Null ( Sql, Unnullify )
+import Rel8.Table.Opaleye (fromOrder, unpackspec)
+import Rel8.Table.Order (ascTable)
 import Rel8.Type ( DBType, typeInformation )
 import Rel8.Type.Array (arrayTypeName, encodeArrayElement)
 import Rel8.Type.Eq ( DBEq )
 import Rel8.Type.Information (TypeInformation)
-import Rel8.Type.Num ( DBNum )
-import Rel8.Type.Ord ( DBMax, DBMin )
+import Rel8.Type.Num (DBFractional, DBNum)
+import Rel8.Type.Ord (DBMax, DBMin, DBOrd)
 import Rel8.Type.String ( DBString )
 import Rel8.Type.Sum ( DBSum )
 
@@ -239,6 +254,132 @@ stringAggOn :: (Sql IsString a, Sql DBString a)
 stringAggOn delimiter f = lmap f (stringAgg delimiter)
 
 
+-- | Corresponds to @mode() WITHIN GROUP (ORDER BY _)@.
+mode :: Sql DBOrd a => Aggregator1 (Expr a) (Expr a)
+mode =
+  unsafeMakeAggregator
+    id
+    (fromPrimExpr . fromColumn)
+    Empty
+    (Opaleye.withinGroup ((\(Order o) -> o) ascTable)
+      (Opaleye.makeAggrExplicit (pure ()) (Opaleye.AggrOther "mode")))
+
+
+-- | Applies 'mode' to the column selected by the given function.
+modeOn :: Sql DBOrd a => (i -> Expr a) -> Aggregator1 i (Expr a)
+modeOn f = lmap f mode
+
+
+-- | Corresponds to @percentile_disc(_) WITHIN GROUP (ORDER BY _)@.
+percentile :: Sql DBOrd a => Expr Double -> Aggregator1 (Expr a) (Expr a)
+percentile fraction = 
+  unsafeMakeAggregator
+    (\a -> (fraction, a))
+    (castExpr . fromPrimExpr . fromColumn)
+    Empty
+    (Opaleye.withinGroup ((\(Order o) -> o) (snd >$< ascTable))
+      (Opaleye.makeAggrExplicit
+        (lmap fst unpackspec)
+        (Opaleye.AggrOther "percentile_disc")))
+
+
+-- | Applies 'percentile' to the column selected by the given function.
+percentileOn ::
+  Sql DBOrd a =>
+  Expr Double ->
+  (i -> Expr a) ->
+  Aggregator1 i (Expr a)
+percentileOn fraction f = lmap f (percentile fraction)
+
+
+-- | Corresponds to @percentile_cont(_) WITHIN GROUP (ORDER BY _)@.
+percentileContinuous ::
+  Sql DBFractional a =>
+  Expr Double ->
+  Aggregator1 (Expr a) (Expr a)
+percentileContinuous fraction = 
+  unsafeMakeAggregator
+    (\a -> (fraction, a))
+    (castExpr . fromPrimExpr . fromColumn)
+    Empty
+    (Opaleye.withinGroup ((\(Order o) -> o) (unsafeCastExpr @Double . snd >$< asc))
+      (Opaleye.makeAggrExplicit
+        (lmap fst unpackspec)
+        (Opaleye.AggrOther "percentile_disc")))
+
+
+
+-- | Applies 'percentileContinuous' to the column selected by the given
+-- function.
+percentileContinuousOn ::
+  Sql DBFractional a =>
+  Expr Double ->
+  (i -> Expr a) ->
+  Aggregator1 i (Expr a)
+percentileContinuousOn fraction f = lmap f (percentileContinuous fraction)
+
+
+-- | Corresponds to @rank(_) WITHIN GROUP (ORDER BY _)@.
+hypotheticalRank ::
+  Order a ->
+  a ->
+  Aggregator' fold a (Expr Int64)
+hypotheticalRank (Order order) args = 
+  unsafeMakeAggregator
+    (\a -> (args, a))
+    (castExpr . fromPrimExpr . fromColumn)
+    (Fallback 1)
+    (Opaleye.withinGroup (snd >$< order)
+      (Opaleye.makeAggrExplicit
+        (fromOrder (fst >$< order))
+        (Opaleye.AggrOther "rank")))
+
+
+-- | Corresponds to @dense_rank(_) WITHIN GROUP (ORDER BY _)@.
+hypotheticalDenseRank ::
+  Order a ->
+  a ->
+  Aggregator' fold a (Expr Int64)
+hypotheticalDenseRank (Order order) args = 
+  unsafeMakeAggregator
+    (const args)
+    (castExpr . fromPrimExpr . fromColumn)
+    (Fallback 1)
+    (Opaleye.withinGroup order
+      (Opaleye.makeAggrExplicit (fromOrder order)
+        (Opaleye.AggrOther "dense_rank")))
+
+
+-- | Corresponds to @percent_rank(_) WITHIN GROUP (ORDER BY _)@.
+hypotheticalPercentRank ::
+  Order a ->
+  a ->
+  Aggregator' fold a (Expr Double)
+hypotheticalPercentRank (Order order) args = 
+  unsafeMakeAggregator
+    (const args)
+    (castExpr . fromPrimExpr . fromColumn)
+    (Fallback 0)
+    (Opaleye.withinGroup order
+      (Opaleye.makeAggrExplicit (fromOrder order)
+        (Opaleye.AggrOther "percent_rank")))
+
+
+-- | Corresponds to @cume_dist(_) WITHIN GROUP (ORDER BY _)@.
+hypotheticalCumeDist ::
+  Order a ->
+  a ->
+  Aggregator' fold a (Expr Double)
+hypotheticalCumeDist (Order order) args = 
+  unsafeMakeAggregator
+    (const args)
+    (castExpr . fromPrimExpr . fromColumn)
+    (Fallback 1)
+    (Opaleye.withinGroup order
+      (Opaleye.makeAggrExplicit (fromOrder order)
+        (Opaleye.AggrOther "cume_dist")))
+
+
 -- | Aggregate a value by grouping by it.
 groupByExpr :: Sql DBEq a => Aggregator1 (Expr a) (Expr a)
 groupByExpr =
@@ -249,7 +390,7 @@ groupByExpr =
     Opaleye.groupBy
 
 
--- | Applies 'groupByExprOn' to the column selected by the given function.
+-- | Applies 'groupByExpr' to the column selected by the given function.
 groupByExprOn :: Sql DBEq a => (i -> Expr a) -> Aggregator1 i (Expr a)
 groupByExprOn f = lmap f groupByExpr
 
diff --git a/src/Rel8/Expr/Num.hs b/src/Rel8/Expr/Num.hs
index 32c06c66..f1f58767 100644
--- a/src/Rel8/Expr/Num.hs
+++ b/src/Rel8/Expr/Num.hs
@@ -33,7 +33,7 @@ fromIntegral :: (Sql DBIntegral a, Sql DBNum b, Homonullable a b)
 fromIntegral (Expr a) = castExpr (Expr a)
 
 
--- | Cast 'DBNum' types to 'DBFractional' types. For example, his can be useful
+-- | Cast 'DBNum' types to 'DBFractional' types. For example, this can be useful
 -- to convert @Expr Float@ to @Expr Double@.
 realToFrac :: (Sql DBNum a, Sql DBFractional b, Homonullable a b)
   => Expr a -> Expr b
diff --git a/src/Rel8/Query/Aggregate.hs b/src/Rel8/Query/Aggregate.hs
index 2e3a215d..1a5348a5 100644
--- a/src/Rel8/Query/Aggregate.hs
+++ b/src/Rel8/Query/Aggregate.hs
@@ -6,13 +6,11 @@ module Rel8.Query.Aggregate
   ( aggregate
   , aggregate1
   , countRows
-  , mode
   )
 where
 
 -- base
 import Control.Applicative (liftA2)
-import Data.Functor.Contravariant ( (>$<) )
 import Data.Int ( Int64 )
 import Prelude
 
@@ -24,15 +22,10 @@ import Rel8.Aggregate (Aggregator' (Aggregator), Aggregator)
 import Rel8.Aggregate.Fold (Fallback (Fallback))
 import Rel8.Expr ( Expr )
 import Rel8.Expr.Aggregate ( countStar )
-import Rel8.Expr.Order ( desc )
 import Rel8.Query ( Query )
-import Rel8.Query.Limit ( limit )
 import Rel8.Query.Maybe ( optional )
 import Rel8.Query.Opaleye ( mapOpaleye )
-import Rel8.Query.Order ( orderBy )
 import Rel8.Table (Table)
-import Rel8.Table.Aggregate (groupBy)
-import Rel8.Table.Eq (EqTable)
 import Rel8.Table.Maybe (fromMaybeTable)
 
 
@@ -55,11 +48,3 @@ aggregate1 (Aggregator _ aggregator) = mapOpaleye (Opaleye.aggregate aggregator)
 -- will return @0@.
 countRows :: Query a -> Query (Expr Int64)
 countRows = aggregate countStar
-
-
--- | Return the most common row in a query.
-mode :: forall a. EqTable a => Query a -> Query a
-mode rows =
-  limit 1 $ fmap snd $
-    orderBy (fst >$< desc) $ do
-      aggregate1 (liftA2 (,) countStar groupBy) rows
diff --git a/src/Rel8/Schema/HTable.hs b/src/Rel8/Schema/HTable.hs
index 477fad14..2642f205 100644
--- a/src/Rel8/Schema/HTable.hs
+++ b/src/Rel8/Schema/HTable.hs
@@ -15,15 +15,17 @@
 
 module Rel8.Schema.HTable
   ( HTable (HField, HConstrainTable)
-  , hfield, htabulate, htraverse, hdicts, hspecs
-  , hfoldMap, hmap, htabulateA, htabulateP, htraverseP, htraversePWithField
+  , hfield, htabulate, hdicts, hspecs
+  , hfoldMap, hmap, htabulateA, htabulateP
+  , htraverse, htraverse_, htraverseP, htraversePWithField
   )
 where
 
 -- base
+import Data.Functor (void)
+import Data.Functor.Compose ( Compose( Compose ), getCompose )
 import Data.Functor.Const ( Const( Const ), getConst )
 import Data.Kind ( Constraint, Type )
-import Data.Functor.Compose ( Compose( Compose ), getCompose )
 import Data.Proxy ( Proxy )
 import GHC.Generics
   ( (:*:)( (:*:) )
@@ -46,7 +48,7 @@ import Rel8.Schema.HTable.Product ( HProduct( HProduct ) )
 import qualified Rel8.Schema.Kind as K
 
 -- semigroupoids
-import Data.Functor.Apply ( Apply, (<.>) )
+import Data.Functor.Apply (Apply, (<.>), liftF2)
 
 -- | A @HTable@ is a functor-indexed/higher-kinded data type that is
 -- representable ('htabulate'/'hfield'), constrainable ('hdicts'), and
@@ -130,6 +132,20 @@ hmap :: HTable t
 hmap f a = htabulate $ \field -> f (hfield a field)
 
 
+newtype Ap f a = Ap
+  { getAp :: f a
+  }
+
+
+instance (Apply f, Semigroup a) => Semigroup (Ap f a) where
+  Ap a <> Ap b = Ap (liftF2 (<>) a b)
+
+
+htraverse_ :: (HTable t, Apply f)
+  => (forall a. context a -> f b) -> t context -> f ()
+htraverse_ f a = getAp $ hfoldMap (Ap . void . f) a
+
+
 htabulateA :: (HTable t, Apply m)
   => (forall a. HField t a -> m (context a)) -> m (t context)
 htabulateA f = htraverse getCompose $ htabulate $ Compose . f
diff --git a/src/Rel8/Table/Opaleye.hs b/src/Rel8/Table/Opaleye.hs
index 8a168962..3f468b26 100644
--- a/src/Rel8/Table/Opaleye.hs
+++ b/src/Rel8/Table/Opaleye.hs
@@ -23,10 +23,12 @@ module Rel8.Table.Opaleye
   , valuesspec
   , view
   , castTable
+  , fromOrder
   )
 where
 
 -- base
+import Data.Foldable (traverse_)
 import Data.Functor.Const ( Const( Const ), getConst )
 import Data.List.NonEmpty ( NonEmpty )
 import Prelude
@@ -36,6 +38,9 @@ import qualified Opaleye.Adaptors as Opaleye
 import qualified Opaleye.Field as Opaleye ( Field_ )
 import qualified Opaleye.Internal.HaskellDB.PrimQuery as Opaleye
 import qualified Opaleye.Internal.Operators as Opaleye
+import qualified Opaleye.Internal.Order as Opaleye
+import qualified Opaleye.Internal.PackMap as Opaleye
+import qualified Opaleye.Internal.Unpackspec as Opaleye
 import qualified Opaleye.Internal.Values as Opaleye
 import qualified Opaleye.Table as Opaleye
 
@@ -48,8 +53,10 @@ import Rel8.Expr.Opaleye
   ( fromPrimExpr, toPrimExpr
   , scastExpr, traverseFieldP
   )
-import Rel8.Schema.HTable ( htabulateA, hfield, hspecs, htabulate,
-                            htraverseP, htraversePWithField )
+import Rel8.Schema.HTable
+  ( htabulateA, hfield, hspecs, htabulate
+  , htraverseP, htraversePWithField
+  )
 import Rel8.Schema.Name ( Name( Name ), Selects, ppColumn )
 import Rel8.Schema.QualifiedName (QualifiedName (QualifiedName))
 import Rel8.Schema.Spec ( Spec(..) )
@@ -153,3 +160,9 @@ castTable (toColumns -> as) = fromColumns $ htabulate \field ->
   case hfield hspecs field of
     Spec {info} -> case hfield as field of
         expr -> scastExpr info expr
+
+
+fromOrder :: Opaleye.Order a -> Opaleye.Unpackspec a a
+fromOrder (Opaleye.Order o) =
+  Opaleye.Unpackspec $ Opaleye.PackMap $ \f a ->
+    a <$ traverse_ (f . snd) (o a)
diff --git a/src/Rel8/Type/Eq.hs b/src/Rel8/Type/Eq.hs
index 02e11273..426f8c65 100644
--- a/src/Rel8/Type/Eq.hs
+++ b/src/Rel8/Type/Eq.hs
@@ -14,9 +14,10 @@ where
 import Data.Aeson ( Value )
 
 -- base
-import Data.List.NonEmpty ( NonEmpty )
+import Data.Fixed (Fixed)
 import Data.Int ( Int16, Int32, Int64 )
 import Data.Kind ( Constraint, Type )
+import Data.List.NonEmpty ( NonEmpty )
 import Prelude
 
 -- bytestring
@@ -29,6 +30,7 @@ import Data.CaseInsensitive ( CI )
 -- rel8
 import Rel8.Schema.Null ( Sql )
 import Rel8.Type ( DBType )
+import Rel8.Type.Decimal (PowerOf10)
 
 -- scientific
 import Data.Scientific ( Scientific )
@@ -58,6 +60,7 @@ instance DBEq Char
 instance DBEq Int16
 instance DBEq Int32
 instance DBEq Int64
+instance PowerOf10 n => DBEq (Fixed n)
 instance DBEq Float
 instance DBEq Double
 instance DBEq Scientific
diff --git a/src/Rel8/Type/Num.hs b/src/Rel8/Type/Num.hs
index da13ef09..98c04e89 100644
--- a/src/Rel8/Type/Num.hs
+++ b/src/Rel8/Type/Num.hs
@@ -12,12 +12,14 @@ module Rel8.Type.Num
 where
 
 -- base
+import Data.Fixed (Fixed)
 import Data.Int ( Int16, Int32, Int64 )
 import Data.Kind ( Constraint, Type )
 import Prelude
 
 -- rel8
 import Rel8.Type ( DBType )
+import Rel8.Type.Decimal (PowerOf10)
 import Rel8.Type.Ord ( DBOrd )
 
 -- scientific
@@ -31,6 +33,7 @@ class DBType a => DBNum a
 instance DBNum Int16
 instance DBNum Int32
 instance DBNum Int64
+instance PowerOf10 n => DBNum (Fixed n)
 instance DBNum Float
 instance DBNum Double
 instance DBNum Scientific
@@ -49,6 +52,7 @@ instance DBIntegral Int64
 -- | The class of database types that support the @/@ operator.
 type DBFractional :: Type -> Constraint
 class DBNum a => DBFractional a
+instance PowerOf10 n => DBFractional (Fixed n)
 instance DBFractional Float
 instance DBFractional Double
 instance DBFractional Scientific
diff --git a/src/Rel8/Type/Ord.hs b/src/Rel8/Type/Ord.hs
index a89c40fa..5b67d8eb 100644
--- a/src/Rel8/Type/Ord.hs
+++ b/src/Rel8/Type/Ord.hs
@@ -12,6 +12,7 @@ module Rel8.Type.Ord
 where
 
 -- base
+import Data.Fixed (Fixed)
 import Data.Int ( Int16, Int32, Int64 )
 import Data.Kind ( Constraint, Type )
 import Data.List.NonEmpty ( NonEmpty )
@@ -26,6 +27,7 @@ import Data.CaseInsensitive ( CI )
 
 -- rel8
 import Rel8.Schema.Null ( Sql )
+import Rel8.Type.Decimal (PowerOf10)
 import Rel8.Type.Eq ( DBEq )
 
 -- scientific
@@ -53,6 +55,7 @@ instance DBOrd Char
 instance DBOrd Int16
 instance DBOrd Int32
 instance DBOrd Int64
+instance PowerOf10 n => DBOrd (Fixed n)
 instance DBOrd Float
 instance DBOrd Double
 instance DBOrd Scientific
@@ -79,6 +82,7 @@ instance DBMax Char
 instance DBMax Int16
 instance DBMax Int32
 instance DBMax Int64
+instance PowerOf10 n => DBMax (Fixed n)
 instance DBMax Float
 instance DBMax Double
 instance DBMax Scientific
@@ -104,6 +108,7 @@ instance DBMin Char
 instance DBMin Int16
 instance DBMin Int32
 instance DBMin Int64
+instance PowerOf10 n => DBMin (Fixed n)
 instance DBMin Float
 instance DBMin Double
 instance DBMin Scientific
diff --git a/src/Rel8/Type/Sum.hs b/src/Rel8/Type/Sum.hs
index 3808b321..3daeb360 100644
--- a/src/Rel8/Type/Sum.hs
+++ b/src/Rel8/Type/Sum.hs
@@ -12,12 +12,14 @@ module Rel8.Type.Sum
 where
 
 -- base
+import Data.Fixed (Fixed)
 import Data.Int ( Int16, Int32, Int64 )
 import Data.Kind ( Constraint, Type )
 import Prelude
 
 -- rel8
 import Rel8.Type ( DBType )
+import Rel8.Type.Decimal (PowerOf10)
 
 -- scientific
 import Data.Scientific ( Scientific )
@@ -32,6 +34,7 @@ class DBType a => DBSum a
 instance DBSum Int16
 instance DBSum Int32
 instance DBSum Int64
+instance PowerOf10 n => DBSum (Fixed n)
 instance DBSum Float
 instance DBSum Double
 instance DBSum Scientific