Call sqlite3_clear_bindings() in bind() to reset parameters

Closes #1063

sqlite3.go

@@ -1958,6 +1958,8 @@ func (s *SQLiteStmt) bind(args []driver.NamedValue) error {
 		return s.c.lastError()
 	}
 
+	C.sqlite3_clear_bindings(s.s)
+
 	bindIndices := make([][3]int, len(args))
 	prefixes := []string{":", "@", "$"}
 	for i, v := range args {

sqlite3_test.go

@@ -2023,6 +2023,48 @@ func TestNamedParam(t *testing.T) {
 	}
 }
 
+func TestNamedParamClearBindings(t *testing.T) {
+	tempFilename := TempFilename(t)
+	defer os.Remove(tempFilename)
+	db, err := sql.Open("sqlite3", tempFilename)
+	if err != nil {
+		t.Fatal("Failed to open database:", err)
+	}
+	defer db.Close()
+
+	_, err = db.Exec("create table foo (x integer, y integer, z text)")
+	if err != nil {
+		t.Fatal("Failed to create table:", err)
+	}
+
+	// First insert with all named params specified
+	_, err = db.Exec("insert into foo(x, y, z) values($x, $y, $z)",
+		sql.Named("x", 1), sql.Named("y", 2), sql.Named("z", "three"))
+	if err != nil {
+		t.Fatal("Failed to insert:", err)
+	}
+
+	// Second insert: $y should be NULL since we pass nil explicitly
+	_, err = db.Exec("insert into foo(x, y, z) values($x, $y, $z)",
+		sql.Named("x", 10), sql.Named("y", nil), sql.Named("z", nil))
+	if err != nil {
+		t.Fatal("Failed to insert:", err)
+	}
+
+	var x int
+	var y, z sql.NullInt64
+	err = db.QueryRow("select x, y, z from foo where x = 10").Scan(&x, &y, &z)
+	if err != nil {
+		t.Fatal("Failed to query:", err)
+	}
+	if y.Valid {
+		t.Errorf("Expected y to be NULL, got %d", y.Int64)
+	}
+	if z.Valid {
+		t.Errorf("Expected z to be NULL, got %d", z.Int64)
+	}
+}
+
 var customFunctionOnce sync.Once
 
 func BenchmarkCustomFunctions(b *testing.B) {