SQL question brushing and sorting in leetcode of partial deduction

1873. Calculate special bonuses

select employee_id,
case
when employee_id in (select employee_id from Employees where name not like "M%" and employee_id%2=1) then salary
else 0 
end as bonus
from Employees
order by employee_id;

practice case when...then... when...then... else... end Judgment statement , The results are stored in end In the field immediately following .

196. Delete duplicate email

DELETE p1 from Person p1 join Person p2 on p1.email=p2.email and p1.id>p2.id;

The title requires the use of delete sentence , You can use first select do .

Input

Person surface :
+---+-------+
| id | email |
+---+-------+
| 1  | A       |
| 2  | B      |
| 3  | A       |
+---+-------+

Through the first select View all results

select * from Person p1 join Person p2 on p1.email=p2.email;

The result is ：（ The fields from left to right are ：p1.id,p1.email,p2.id,p2.email）

1 A 1 A

3 A 1 A

2 B 2 B

1 A 3 A

3 A 3 A

According to the title , Try to delete 3 A that will do ,

if delete p1（ Just look at the first two fields ） Add criteria to filter out 3 A 1 A perhaps 3 A 3 A,

if delete p2（ Just look at the last two fields ） Add criteria to filter out 1 A 3 A perhaps 3 A 3 A,

If you want to filter out 3 A 3 A, Only use p1.id=p2.id, here 1 A 1 A and 2 B 2 B Will also be screened out , It doesn't fit the question ,

therefore about delete p1 Only use p1.id>p2.id, about delete p1 Only use p1.id<p2.id.

1484. Sell products by date

select
sell_date,
count(distinct product) num_sold,
group_concat(distinct product order by product asc separator ',') products
from
Activities
group by
sell_date;

group_concat： Connect the data in the group

distinct： By default, they are arranged in ascending field order , To change the sort by order by modify

order by product asc separator ','：distinct Default ascending order ,group_concat Default ‘,’ Connect , So this paragraph sql It can be omitted