在对表格进行分组时避免重复值

Question

表：员工

empid depti salary hired_date
1   1   4000    2012-01-01
2   1   3000    2015-11-01
3   1   3000    2015-01-11
4   2   4000    2015-11-01
5   1   3000    2014-11-01
6   2   5000    2015-01-01

查询：

select emp1.empid, emp1.salary as higher, emp2.empid, emp2.salary as lower_sal
from employee as emp1, employee as emp2
where emp1.salary >= 4000 and emp2.salary < 4000 
group by emp1.empid, emp2.empid, emp1.salary, emp2.salary

以上查询结果：

empid higher empid lower_sal
1   4000    2   3000
1   4000    3   3000
1   4000    5   3000
4   4000    2   3000
4   4000    3   3000
4   4000    5   3000
6   5000    2   3000
6   5000    3   3000
6   5000    5   3000

预期结果：

empid higher empid lower_sal
1   4000    2   3000
4   4000    3   3000
6   5000    5   3000

需要在查询中包含哪些内容才能获得此输出并避免重复值。

Answer 1

你尝试过使用distinct吗？这是您可以添加的子句，表示您不需要重复值。在“选择”之后添加。

select distinct emp1.empid, emp1.salary as higher, emp2.empid, emp2.salary as lower_sal
from employee as emp1, employee as emp2
where emp1.salary >= 4000 and emp2.salary < 4000 
group by emp1.empid, emp2.empid, emp1.salary, emp2.salary

Answer 2

根据我的理解，您可以使用交叉申请，

SELECT      *
FROM        Employee A
CROSS APPLY (SELECT Min(B.Salary) AS Min_Salary
             FROM   Employee B
             WHERE B.salary < 4000)B 
WHERE  A.Salary >= 4000

Answer 3

尝试以下查询

$first_letter = mb_strtoupper(substr(apply_filters('the_title',$post->post_title),0,1), 'UTF-8');

结果如下所示