More tests.

ext/stats/TODO.md

@@ -44,4 +44,12 @@ https://sqlite.org/lang_aggfunc.html
 - [ ] `PERCENTILE_CONT(percentile) OVER window`
 - [ ] `PERCENTILE_DISC(percentile) OVER window`
 
-https://sqlite.org/windowfunctions.html#builtins
+https://sqlite.org/windowfunctions.html#builtins
+
+## Additional aggregates
+
+- [X] `MEDIAN(expression)`
+- [X] `QUANTILE_CONT(expression, quantile)`
+- [X] `QUANTILE_DISC(expression, quantile)`
+
+https://duckdb.org/docs/sql/aggregates.html

ext/stats/quantile.go

@@ -35,7 +35,7 @@ func (q *quantile) Step(ctx sqlite3.Context, arg ...sqlite3.Value) {
 }
 
 func (q *quantile) Value(ctx sqlite3.Context) {
-	if q.list == nil {
+	if len(q.list) == 0 {
 		return
 	}
 	if q.kind == median {
@@ -49,7 +49,7 @@ func (q *quantile) Value(ctx sqlite3.Context) {
 	i, f := math.Modf(q.pos * float64(len(q.list)-1))
 	m0 := quick.Select(q.list, int(i))
 
-	if q.kind == quant_disc {
+	if f == 0 || q.kind == quant_disc {
 		ctx.ResultFloat(m0)
 		return
 	}

ext/stats/quantile_test.go

@@ -34,13 +34,11 @@ func TestRegister_quantile(t *testing.T) {
 		SELECT
 			median(x),
 			quantile_disc(x, 0.5),
-			quantile_cont(x, 0.3)
+			quantile_cont(x, 0.25)
 		FROM data`)
 	if err != nil {
 		t.Fatal(err)
 	}
-	defer stmt.Close()
-
 	if stmt.Step() {
 		if got := stmt.ColumnFloat(0); got != 10 {
 			t.Errorf("got %v, want 10", got)
@@ -48,8 +46,68 @@ func TestRegister_quantile(t *testing.T) {
 		if got := stmt.ColumnFloat(1); got != 7 {
 			t.Errorf("got %v, want 7", got)
 		}
-		if got := stmt.ColumnFloat(2); got != 6.699999999999999 {
-			t.Errorf("got %v, want 6.7", got)
+		if got := stmt.ColumnFloat(2); got != 6.25 {
+			t.Errorf("got %v, want 6.25", got)
 		}
 	}
+	stmt.Close()
+
+	stmt, _, err = db.Prepare(`
+		SELECT
+			median(x),
+			quantile_disc(x, 0.5),
+			quantile_cont(x, 0.25)
+		FROM data
+		WHERE x < 5`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if stmt.Step() {
+		if got := stmt.ColumnFloat(0); got != 4 {
+			t.Errorf("got %v, want 4", got)
+		}
+		if got := stmt.ColumnFloat(1); got != 4 {
+			t.Errorf("got %v, want 4", got)
+		}
+		if got := stmt.ColumnFloat(2); got != 4 {
+			t.Errorf("got %v, want 4", got)
+		}
+	}
+	stmt.Close()
+
+	stmt, _, err = db.Prepare(`
+		SELECT
+			median(x),
+			quantile_disc(x, 0.5),
+			quantile_cont(x, 0.25)
+		FROM data
+		WHERE x < 0`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if stmt.Step() {
+		if got := stmt.ColumnType(0); got != sqlite3.NULL {
+			t.Error("want NULL")
+		}
+		if got := stmt.ColumnType(1); got != sqlite3.NULL {
+			t.Error("want NULL")
+		}
+		if got := stmt.ColumnType(2); got != sqlite3.NULL {
+			t.Error("want NULL")
+		}
+	}
+	stmt.Close()
+
+	stmt, _, err = db.Prepare(`
+		SELECT
+			quantile_disc(x, -2),
+			quantile_cont(x, +2)
+		FROM data`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if stmt.Step() {
+		t.Fatal("want error")
+	}
+	stmt.Close()
 }

ext/stats/stats.go

@@ -18,9 +18,9 @@
 //   - regr_slope: slope of the least-squares-fit linear equation
 //   - regr_intercept: y-intercept of the least-squares-fit linear equation
 //   - regr_json: all regr stats in a JSON object
-//   - median: median value
-//   - quantile_cont: continuous quantile
 //   - quantile_disc: discrete quantile
+//   - quantile_cont: continuous quantile
+//   - median: median value
 //
 // These join the [Built-in Aggregate Functions]:
 //   - count: count rows/values
@@ -29,8 +29,7 @@
 //   - min: minimum value
 //   - max: maximum value
 //
-// See: [ANSI SQL Aggregate Functions]
-// See: [DuckDB Aggregate Functions]
+// See: [ANSI SQL Aggregate Functions], [DuckDB Aggregate Functions]
 //
 // [Built-in Aggregate Functions]: https://sqlite.org/lang_aggfunc.html
 // [ANSI SQL Aggregate Functions]: https://www.oreilly.com/library/view/sql-in-a/9780596155322/ch04s02.html