我的员工表如下：

+-------------+---------+------------------+
| employee_id |  phone  |       dept       |
+-------------+---------+------------------+
|           1 | 7738474 | marketing        |
|           2 | [null]  | marketing        |
|           3 | 9938475 | customer service |
|           4 | 4233474 | customer service |
|           5 | 1738477 | marketing        |
|           6 | [null]  | marketing        |
|           7 | [null]  | customer service |
+-------------+---------+------------------+

我想如果市场部有空电话值，他们不显示，如果客户服务部，他们显示所有的价值，即使电话是空的

+-------------+---------+------------------+
| employee_id |  phone  |       dept       |
+-------------+---------+------------------+
|           1 | 7738474 | marketing        |
|           3 | 9938475 | customer service |
|           4 | 4233474 | customer service |
|           5 | 1738477 | marketing        |
|           7 | [null]  | customer service |
+-------------+---------+------------------+

有没有不使用union的查询？

select * from employee where dept ='customer service'
union ALL 
select * from employee where dept = 'marketing' and phone is not null