USING Keyword vs ON clause - MYSQL
The USING clause
TheUSINGclause is used if several columns share the same name but you don’t want to join using all of these common columns. The columns listed in the USING clause can’t have any qualifiers in the statement, including the WHERE clause.
The ON clause
TheONclause is used to join tables where the column names don’t match in both tables. The join conditions are removed from the filter conditions in the WHERE clause.
https://leetcode.com/problems/combine-two-tables/
175. Combine Two Tables
Table:
Person+-------------+---------+ | Column Name | Type | +-------------+---------+ | PersonId | int | | FirstName | varchar | | LastName | varchar | +-------------+---------+ PersonId is the primary key column for this table.
Table:
Address+-------------+---------+ | Column Name | Type | +-------------+---------+ | AddressId | int | | PersonId | int | | City | varchar | | State | varchar | +-------------+---------+ AddressId is the primary key column for this table.
Write a SQL query for a report that provides the following information for each person in the Person table, regardless if there is an address for each of those people:
FirstName, LastName, City, State
# Write your MySQL query statement below
from Person left join Address
on Person.PersonId = Address.PersonId
;
577. Employee Bonus
https://leetcode.com/problems/employee-bonus/
Select all employee's name and bonus whose bonus is < 1000.
Table:
Employee+-------+--------+-----------+--------+ | empId | name | supervisor| salary | +-------+--------+-----------+--------+ | 1 | John | 3 | 1000 | | 2 | Dan | 3 | 2000 | | 3 | Brad | null | 4000 | | 4 | Thomas | 3 | 4000 | +-------+--------+-----------+--------+ empId is the primary key column for this table.
Table:
Bonus+-------+-------+ | empId | bonus | +-------+-------+ | 2 | 500 | | 4 | 2000 | +-------+-------+ empId is the primary key column for this table.
Example ouput:
+-------+-------+ | name | bonus | +-------+-------+ | John | null | | Dan | 500 | | Brad | null | +-------+-------+
#select empId, name, bonus #ERR, Column 'empId' in field list is ambiguous
#select Employee.empId, name, bonus #ERR, Column 'empId' in field list is not need
#select Employee.name, Bonus.bonus #ok
select name, bonus #ok
from Employee
left outer join Bonus
on Employee.empId = Bonus.empId
#where Bonus.bonus between 0 and 1000 or bonus is null #ok, not best
where bonus < 1000 OR bonus IS NULL
;
1082. Sales Analysis I
Table:
Product+--------------+---------+ | Column Name | Type | +--------------+---------+ | product_id | int | | product_name | varchar | | unit_price | int | +--------------+---------+ product_id is the primary key of this table.
Table:
Sales+-------------+---------+ | Column Name | Type | +-------------+---------+ | seller_id | int | | product_id | int | | buyer_id | int | | sale_date | date | | quantity | int | | price | int | +------ ------+---------+ This table has no primary key, it can have repeated rows. product_id is a foreign key to Product table.
Write an SQL query that reports the best seller by total sales price, If there is a tie, report them all.
The query result format is in the following example:
Product table:
+------------+--------------+------------+
| product_id | product_name | unit_price |
+------------+--------------+------------+
| 1 | S8 | 1000 |
| 2 | G4 | 800 |
| 3 | iPhone | 1400 |
+------------+--------------+------------+
Sales table:
+-----------+------------+----------+------------+----------+-------+
| seller_id | product_id | buyer_id | sale_date | quantity | price |
+-----------+------------+----------+------------+----------+-------+
| 1 | 1 | 1 | 2019-01-21 | 2 | 2000 |
| 1 | 2 | 2 | 2019-02-17 | 1 | 800 |
| 2 | 2 | 3 | 2019-06-02 | 1 | 800 |
| 3 | 3 | 4 | 2019-05-13 | 2 | 2800 |
+-----------+------------+----------+------------+----------+-------+
Result table:
+-------------+
| seller_id |
+-------------+
| 1 |
| 3 |
+-------------+
Both sellers with id 1 and 3 sold products with the most total price of 2800.
# Write your MySQL query statement below
SELECT seller_id
FROM Sales
GROUP BY seller_id
HAVING sum(price) =
(
SELECT sum(price)
FROM sales
group by seller_id
order by sum(price) desc
limit 1
)
#way2:
SELECT seller_id
FROM Sales
GROUP BY seller_id
Having SUM(price)=(SELECT SUM(price)AS total
FROM Sales S
GROUP BY seller_id
ORDER BY total DESC
LIMIT 1)
1083. Sales Analysis II
Table:
Product+--------------+---------+ | Column Name | Type | +--------------+---------+ | product_id | int | | product_name | varchar | | unit_price | int | +--------------+---------+ product_id is the primary key of this table.
Table:
Sales+-------------+---------+ | Column Name | Type | +-------------+---------+ | seller_id | int | | product_id | int | | buyer_id | int | | sale_date | date | | quantity | int | | price | int | +------ ------+---------+ This table has no primary key, it can have repeated rows. product_id is a foreign key to Product table.
Write an SQL query that reports the buyers who have bought S8 but not iPhone. Note that S8 and iPhone are products present in the
Product table.
The query result format is in the following example:
Product table:
+------------+--------------+------------+
| product_id | product_name | unit_price |
+------------+--------------+------------+
| 1 | S8 | 1000 |
| 2 | G4 | 800 |
| 3 | iPhone | 1400 |
+------------+--------------+------------+
Sales table:
+-----------+------------+----------+------------+----------+-------+
| seller_id | product_id | buyer_id | sale_date | quantity | price |
+-----------+------------+----------+------------+----------+-------+
| 1 | 1 | 1 | 2019-01-21 | 2 | 2000 |
| 1 | 2 | 2 | 2019-02-17 | 1 | 800 |
| 2 | 1 | 3 | 2019-06-02 | 1 | 800 |
| 3 | 3 | 3 | 2019-05-13 | 2 | 2800 |
+-----------+------------+----------+------------+----------+-------+
Result table:
+-------------+
| buyer_id |
+-------------+
| 1 |
+-------------+
The buyer with id 1 bought an S8 but didn't buy an iPhone. The buyer with id 3 bought both.
# Write your MySQL query statement below
/* Way1: ok
select distinct buyer_id
from sales join product using(product_id)
where product_name = 'S8'
and buyer_id not in (select distinct buyer_id
from sales join product using(product_id)
where product_name = 'iPhone' )
*/
SELECT s.buyer_id
FROM Sales AS s INNER JOIN Product AS p
ON s.product_id = p.product_id
GROUP BY s.buyer_id
HAVING SUM(CASE WHEN p.product_name = 'S8' THEN 1 ELSE 0 END) > 0
AND SUM(CASE WHEN p.product_name = 'iPhone' THEN 1 ELSE 0 END) = 0;
1084. Sales Analysis III
Table:
Product+--------------+---------+ | Column Name | Type | +--------------+---------+ | product_id | int | | product_name | varchar | | unit_price | int | +--------------+---------+ product_id is the primary key of this table.
Table:
Sales+-------------+---------+ | Column Name | Type | +-------------+---------+ | seller_id | int | | product_id | int | | buyer_id | int | | sale_date | date | | quantity | int | | price | int | +------ ------+---------+ This table has no primary key, it can have repeated rows. product_id is a foreign key to Product table.
Write an SQL query that reports the products that were only sold in spring 2019. That is, between 2019-01-01 and 2019-03-31 inclusive.
The query result format is in the following example:
Product table:
+------------+--------------+------------+
| product_id | product_name | unit_price |
+------------+--------------+------------+
| 1 | S8 | 1000 |
| 2 | G4 | 800 |
| 3 | iPhone | 1400 |
+------------+--------------+------------+
Sales table:
+-----------+------------+----------+------------+----------+-------+
| seller_id | product_id | buyer_id | sale_date | quantity | price |
+-----------+------------+----------+------------+----------+-------+
| 1 | 1 | 1 | 2019-01-21 | 2 | 2000 |
| 1 | 2 | 2 | 2019-02-17 | 1 | 800 |
| 2 | 2 | 3 | 2019-06-02 | 1 | 800 |
| 3 | 3 | 4 | 2019-05-13 | 2 | 2800 |
+-----------+------------+----------+------------+----------+-------+
Result table:
+-------------+--------------+
| product_id | product_name |
+-------------+--------------+
| 1 | S8 |
+-------------+--------------+
The product with id 1 was only sold in spring 2019 while the other two were sold after.
# Write your MySQL query statement below
#Solution1:
SELECT s.product_id, product_name
FROM Sales s
LEFT JOIN Product p
ON s.product_id = p.product_id
GROUP BY s.product_id
HAVING MIN(sale_date) >= CAST('2019-01-01' AS DATE) AND
MAX(sale_date) <= CAST('2019-03-31' AS DATE)
#Solution2:
SELECT product_id, product_name
FROM Sales
LEFT JOIN Product #same as JOIN Product
Using(product_id)
GROUP BY product_id
HAVING MIN(sale_date) >= '2019-01-01' AND MAX(sale_date) <= '2019-03-31'
1142. User Activity for the Past 30 Days II
Table:
Activity+---------------+---------+
| Column Name | Type |
+---------------+---------+
| user_id | int |
| session_id | int |
| activity_date | date |
| activity_type | enum |
+---------------+---------+
There is no primary key for this table, it may have duplicate rows.
The activity_type column is an ENUM of type ('open_session', 'end_session', 'scroll_down', 'send_message').
The table shows the user activities for a social media website.
Note that each session belongs to exactly one user.
Write an SQL query to find the average number of sessions per user for a period of 30 days ending 2019-07-27 inclusively, rounded to 2 decimal places. The sessions we want to count for a user are those with at least one activity in that time period.
The query result format is in the following example:
Activity table: +---------+------------+---------------+---------------+ | user_id | session_id | activity_date | activity_type | +---------+------------+---------------+---------------+ | 1 | 1 | 2019-07-20 | open_session | | 1 | 1 | 2019-07-20 | scroll_down | | 1 | 1 | 2019-07-20 | end_session | | 2 | 4 | 2019-07-20 | open_session | | 2 | 4 | 2019-07-21 | send_message | | 2 | 4 | 2019-07-21 | end_session | | 3 | 2 | 2019-07-21 | open_session | | 3 | 2 | 2019-07-21 | send_message | | 3 | 2 | 2019-07-21 | end_session | | 3 | 5 | 2019-07-21 | open_session | | 3 | 5 | 2019-07-21 | scroll_down | | 3 | 5 | 2019-07-21 | end_session | | 4 | 3 | 2019-06-25 | open_session | | 4 | 3 | 2019-06-25 | end_session | +---------+------------+---------------+---------------+ Result table: +---------------------------+ | average_sessions_per_user | +---------------------------+ | 1.33 | +---------------------------+ User 1 and 2 each had 1 session in the past 30 days while user 3 had 2 sessions so the average is (1 + 1 + 2) / 3 = 1.33.
# Write your MySQL query statement below
from activity
where activity_date <= '2019-07-27' and activity_date > '2019-06-27'
#Way2:
select round(coalesce(avg(n_session),0),2) average_sessions_per_user
from
(select count(distinct session_id) n_session
from activity
where activity_date between '2019-06-28' and '2019-07-27'
group by user_id) a;
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