Add missing sqlite conditional functions.

tests/sqlite/select_test.go

@@ -810,3 +810,75 @@ func TestScanNumericToNumber(t *testing.T) {
 	require.Equal(t, number.Float32, float32(1.234568e+09))
 	require.Equal(t, number.Float64, float64(1.234567890111e+09))
 }
+
+func TestConditionalFunctions(t *testing.T) {
+	stmt := SELECT(
+		EXISTS(
+			Film.SELECT(Film.FilmID).WHERE(Film.RentalDuration.GT(Int(5))),
+		).AS("exists"),
+		CASE(Film.Length.GT(Int(120))).
+			WHEN(Bool(true)).THEN(String("long film")).
+			ELSE(String("short film")).AS("case"),
+		COALESCE(Film.Description, String("none")).AS("coalesce"),
+		NULLIF(Film.ReleaseYear, Int(200)).AS("null_if"),
+	).FROM(
+		Film,
+	).WHERE(
+		Film.FilmID.LT(Int(5)),
+	).ORDER_BY(
+		Film.FilmID,
+	)
+
+	testutils.AssertDebugStatementSql(t, stmt, `
+SELECT (EXISTS (
+          SELECT film.film_id AS "film.film_id"
+          FROM film
+          WHERE film.rental_duration > 5
+     )) AS "exists",
+     (CASE (film.length > 120) WHEN TRUE THEN 'long film' ELSE 'short film' END) AS "case",
+     COALESCE(film.description, 'none') AS "coalesce",
+     NULLIF(film.release_year, 200) AS "null_if"
+FROM film
+WHERE film.film_id < 5
+ORDER BY film.film_id;
+`)
+
+	var res []struct {
+		Exists   bool
+		Case     string
+		Coalesce string
+		NullIf   string
+	}
+
+	err := stmt.Query(db, &res)
+	require.NoError(t, err)
+
+	testutils.AssertJSON(t, res, `
+[
+	{
+		"Exists": true,
+		"Case": "short film",
+		"Coalesce": "A Epic Drama of a Feminist And a Mad Scientist who must Battle a Teacher in The Canadian Rockies",
+		"NullIf": "2006"
+	},
+	{
+		"Exists": true,
+		"Case": "short film",
+		"Coalesce": "A Astounding Epistle of a Database Administrator And a Explorer who must Find a Car in Ancient China",
+		"NullIf": "2006"
+	},
+	{
+		"Exists": true,
+		"Case": "short film",
+		"Coalesce": "A Astounding Reflection of a Lumberjack And a Car who must Sink a Lumberjack in A Baloon Factory",
+		"NullIf": "2006"
+	},
+	{
+		"Exists": true,
+		"Case": "short film",
+		"Coalesce": "A Fanciful Documentary of a Frisbee And a Lumberjack who must Chase a Monkey in A Shark Tank",
+		"NullIf": "2006"
+	}
+]
+`)
+}