create table test_data
(
    id   bigint not null primary key auto_increment,
    name varchar(100) null
);
insert into test_data
values (1, '1');
insert into test_data
values (2, '2');

var sql = """
select * from test_data
<where>
    <if test='id != null'>
        and id = #{id}
    </if>
</where>
"""
return db.select(sql)

select * from test_data WHERE

select * from test_data