[Postgres] Add order set aggregate functions support.

internal/jet/order_set_aggregate_functions.go

@@ -0,0 +1,60 @@
+package jet
+
+// MODE computes the most frequent value of the aggregated argument
+func MODE() *OrderSetAggregateFunc {
+	return newOrderSetAggregateFunction("MODE", nil)
+}
+
+// PERCENTILE_CONT computes a value corresponding to the specified fraction within the ordered set of
+// aggregated argument values. This will interpolate between adjacent input items if needed.
+func PERCENTILE_CONT(fraction FloatExpression) *OrderSetAggregateFunc {
+	return newOrderSetAggregateFunction("PERCENTILE_CONT", fraction)
+}
+
+// PERCENTILE_DISC computes  the first value within the ordered set of aggregated argument values whose position
+// in the ordering equals or exceeds the specified fraction. The aggregated argument must be of a sortable type.
+func PERCENTILE_DISC(fraction FloatExpression) *OrderSetAggregateFunc {
+	return newOrderSetAggregateFunction("PERCENTILE_DISC", fraction)
+}
+
+// OrderSetAggregateFunc implementation of order set aggregate function
+type OrderSetAggregateFunc struct {
+	name     string
+	fraction FloatExpression
+	orderBy  Window
+}
+
+func newOrderSetAggregateFunction(name string, fraction FloatExpression) *OrderSetAggregateFunc {
+	return &OrderSetAggregateFunc{
+		name:     name,
+		fraction: fraction,
+	}
+}
+
+// WITHIN_GROUP_ORDER_BY specifies ordered set of aggregated argument values
+func (p *OrderSetAggregateFunc) WITHIN_GROUP_ORDER_BY(orderBy OrderByClause) Expression {
+	p.orderBy = ORDER_BY(orderBy)
+	return newOrderSetAggregateFuncExpression(*p)
+}
+
+func newOrderSetAggregateFuncExpression(aggFunc OrderSetAggregateFunc) *orderSetAggregateFuncExpression {
+	ret := &orderSetAggregateFuncExpression{
+		OrderSetAggregateFunc: aggFunc,
+	}
+
+	ret.ExpressionInterfaceImpl.Parent = ret
+
+	return ret
+}
+
+type orderSetAggregateFuncExpression struct {
+	ExpressionInterfaceImpl
+	OrderSetAggregateFunc
+}
+
+func (p *orderSetAggregateFuncExpression) serialize(statement StatementType, out *SQLBuilder, options ...SerializeOption) {
+	out.WriteString(p.name)
+	WRAP(p.fraction).serialize(statement, out, FallTrough(options)...)
+	out.WriteString("WITHIN GROUP")
+	p.orderBy.serialize(statement, out)
+}

internal/jet/utils.go

@@ -34,7 +34,9 @@ func serializeExpressionList(
 			out.WriteString(separator)
 		}
 
-		expression.serialize(statement, out, options...)
+		if expression != nil {
+			expression.serialize(statement, out, options...)
+		}
 	}
 }