src/main/java/com/conveyal/gtfs/loader/Table.java
public String generateDeleteSql (String namespace, String fieldName) {
        String whereField = fieldName == null ? "id" : fieldName;
        return String.format("delete from %s where %s = ?", String.join(".", namespace, name), whereField);
    }
public String generateDeleteSql (String namespace, String fieldName) {
        String whereField = fieldName == null ? "id" : fieldName;
        return String.format("delete from %s where %s = ?", String.join(".", namespace, name), whereField);
    }
Generate delete SQL string.