LeetCode(sql)-0722

高频 SQL50

1757

select product_id from Products where low_fats = 'Y' and recyclable = 'Y'

584

select name from customer where referee_id <> 2 or referee_id is null
# 或者
select name from customer where referee_id != 2 or referee_id is null

595

select name,population,area from World where area >= 3000000 or population >=25000000

1148

select distinct author_id as id from Views where author_id = viewer_id order by author_id

1683

select tweet_id from Tweets where length(content) > 15

1378

左链接的使用

select EmployeeUNI.unique_id,name 
from Employees left join EmployeeUNI on EmployeeUNI.id = Employees.id

1068

使用 关联字段相同时使用using 字句

select product_name,year,price 
from Sales join Product using(product_id)

1581

使用左连接：A 交 B 的补集，group by 统计

select customer_id,count(*) as count_no_trans 
from Visits left join Transactions 
using(visit_id) 
where Transactions.visit_id is null
group by customer_id

197

# 利用 AddDate
select w2.id 
from Weather w1 cross join Weather w2 
on AddDate(w1.recordDate,interval  1 day) = w2.recordDate 
where w1.temperature < w2.temperature

# 利用 DateDiff
select w2.id 
from Weather w1 cross join Weather w2 
on DateDiff(w2.recordDate, w1.recordDate) = 1
where w1.temperature < w2.temperature

1661

平均值的使用，保留 3 位小数

select machine_id,Round(avg(a2.timestamp-a1.timestamp),3) as processing_time
from Activity a1 cross join Activity a2
using(machine_id,process_id)
where a1.activity_type = 'start' and a2.activity_type='end'
group by machine_id

577

select name,bonus
from Employee left join Bonus
using(empId)
where bonus < 1000 or bonus is null

1280

三表联查

select s.student_id,student_name,su.subject_name,count(e.subject_name) as attended_exams
from Students s join Subjects su left join Examinations e
on e.student_id = s.student_id
and e.subject_name = su.subject_name
group by s.student_id,su.subject_name
order by s.student_id,su.subject_name

570

嵌套查询，having 的使用

select name 
from Employee e1 join (
    select managerId 
    from Employee 
    group by managerId
    having count(managerId) >=5 
  ) as e2
on e2.managerId = e1.id;

1934

思路一：把两个数据分别查出来，然后做除法

思路二：在一个表里面利用 sum(iif)统计出来做除法，还需要配合 convert 和

select user_id,Round(Coalesce(confirm,0)/total,2) as confirmation_rate
from (
      select user_id,  count(*) as total
      from Signups left join Confirmations
      using(user_id)
      group by user_id
      ) as t1 left join 
      ( 
        select user_id,count(action) as confirm
        from Confirmations 
        where action = 'confirmed'
        group by user_id
      ) as t2
using(user_id)