题解：

select employee_id,name,reports_count,average_age
from Employees t1,(
    select reports_to,count(*) reports_count,round(avg(age)) average_age
    from Employees
    where reports_to is not null
    group by reports_to
) t2
where t1.employee_id=t2.reports_to
order by employee_id asc

题解：

select employee_id,department_id from Employee
group by employee_id
having count(department_id)=1

union 

select employee_id,department_id from Employee
where primary_flag='Y'

select employee_id,department_id from Employee
where primary_flag='Y' or employee_id in (
    select employee_id from Employee
    group by employee_id
    having count(department_id)=1
)

题解：

select x,y,z,
if(x+y>z and x+z>y and y+z>x,'Yes','No') triangle
from Triangle

select x, y, z,
    case
        when x+y>z and x+z>y and y+z>x then 'Yes'
        else 'No'
    end as triangle
from Triangle

题解：

select distinct l1.num ConsecutiveNums from 
Logs l1,
Logs l2,
Logs l3
where l1.id=l2.id+1 and l2.id=l3.id+1
and l1.num=l2.num and l2.num=l3.num