MySQL选择不同的值时工作不正常

我试图使用这个查询从我的工资表中检索不同的值

SELECT DISTINCT gross,sl_month,sl_year 
FROM wp_attn_emp_salary where `emp_id` = 22 order by gross DESC

但它也会返回重复值。请检查图像。

Query Result

我的预期结果是这样的

Array
(
[0] => stdClass Object
    (
        [gross] => 9595
        [sl_month] => 2
        [sl_year] => 2021
    )

[1] => stdClass Object
    (
        [gross] => 9226
        [sl_month] => 1
        [sl_year] => 2020
    )

[2] => stdClass Object
    (
        [gross] => 8875
        [sl_month] => 2
        [sl_year] => 2019
    
    )

[3] => stdClass Object
    (
        [gross] => 8420
        [sl_month] => 1
        [sl_year] => 2019
    )

[4] => stdClass Object
    (
        [gross] => 8405
        [sl_month] => 12
        [sl_year] => 2018
    )

[5] => stdClass Object
    (
        [gross] => 6464
        [sl_month] => 1
        [sl_year] => 2018
    )

)

我也需要按降序排列的sl_月和sl_年。