[force deduction 10 days SQL introduction] Day10 control flow

182. Find duplicate email

 Write a  SQL  Inquire about , lookup  Person  All duplicate email addresses in the table .

 Example ：
+----+---------+
| Id | Email   |
+----+---------+
| 1  | [email protected] |
| 2  | [email protected] |
| 3  | [email protected] |
+----+---------+
 According to the above input , Your query should return the following results ：
+---------+
| Email   |
+---------+
| [email protected] |
+---------+

Analysis of the answer

Group by mailbox , The number is larger than 1 Output

SELECT A.Email
FROM (
    SELECT Email, count(Id) id
    FROM Person
    GROUP BY Email) A
WHERE A.id > 1

solution 2, HAVING Sentences are usually associated with GROUP BY Statements are used in conjunction with , Used to filter by GROUP BY Statement returned recordset .

SELECT Email
FROM Person
GROUP BY Email
HAVING count(Id) > 1

1050. Actors and directors who have worked together at least three times

ActorDirector  surface ：
+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| actor_id    | int     |
| director_id | int     |
| timestamp   | int     |
+-------------+---------+
timestamp  It's the primary key of this table .
 Write a SQL Query statement to get actors and directors who have cooperated at least three times  id  Yes  (actor_id, director_id)

ActorDirector  surface ：
+-------------+-------------+-------------+
| actor_id    | director_id | timestamp   |
+-------------+-------------+-------------+
| 1           | 1           | 0           |
| 1           | 1           | 1           |
| 1           | 1           | 2           |
| 1           | 2           | 3           |
| 1           | 2           | 4           |
| 2           | 1           | 5           |
| 2           | 1           | 6           |
+-------------+-------------+-------------+

Result  surface ：
+-------------+-------------+
| actor_id    | director_id |
+-------------+-------------+
| 1           | 1           |
+-------------+-------------+

Analysis of the answer

SELECT actor_id, director_id
FROM ActorDirector 
GROUP BY actor_id, director_id 
HAVING COUNT(1) >= 3

1587. Bank account summary II

 surface : Users
+--------------+---------+
| Column Name  | Type    |
+--------------+---------+
| account      | int     |
| name         | varchar |
+--------------+---------+
account  Is the primary key of the table . Each row in the table contains the account number of each user in the bank .
 
 surface : Transactions
+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| trans_id      | int     |
| account       | int     |
| amount        | int     |
| transacted_on | date    |
+---------------+---------+
trans_id  Is the primary key of the table . Each row of the table contains the transaction changes of all accounts .
 If the user receives the money ,  Then the amount is positive ;  If the user transfers money ,  Then the amount is negative .
 The starting balance of all accounts is  0.
 
 Write a  SQL,   The reported balance is higher than  10000  The names and balances of all users .  The balance of the account is equal to the sum of all transactions including the account .
 The returned result form has no sequence requirements .


Users table:
+------------+--------------+
| account    | name         |
+------------+--------------+
| 900001     | Alice        |
| 900002     | Bob          |
| 900003     | Charlie      |
+------------+--------------+

Transactions table:
+------------+------------+------------+---------------+
| trans_id   | account    | amount     | transacted_on |
+------------+------------+------------+---------------+
| 1          | 900001     | 7000       |  2020-08-01   |
| 2          | 900001     | 7000       |  2020-09-01   |
| 3          | 900001     | -3000      |  2020-09-02   |
| 4          | 900002     | 1000       |  2020-09-12   |
| 5          | 900003     | 6000       |  2020-08-07   |
| 6          | 900003     | 6000       |  2020-09-07   |
| 7          | 900003     | -4000      |  2020-09-11   |
+------------+------------+------------+---------------+

Result table:
+------------+------------+
| name       | balance    |
+------------+------------+
| Alice      | 11000      |
+------------+------------+

Analysis of the answer

SELECT A.name NAME, sum(B.amount) BALANCE 
FROM Users A LEFT JOIN Transactions B ON A.account = B.account
GROUP BY A.account
HAVING balance > 10000

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 the table .
 Each row of the table shows the name and price of each product .
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 duplicate lines .product_id  yes  Product  Table foreign key .
 Each row of the table contains some information about a sale .
 
 Write a SQL Inquire about , The report 2019 Products sold only in the spring of . namely   Only in 2019-01-01 to 2019-03-31（ contain ） Sale between   The goods .
 With   In any order   Return result table .
 Input ：
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  |
+-----------+------------+----------+------------+----------+-------+
 Output ：
+-------------+--------------+
| product_id  | product_name |
+-------------+--------------+
| 1           | S8           |
+-------------+--------------+
id by 1 Of products are only available in 2019 Spring sales .
id by 2 Our products are in 2019 Spring sales , But also 2019 Sales after spring 2004 .
id 3 Our products are in 2019 Sales after spring 2004 .

Analysis of the answer

SELECT A.product_id, A.product_name
FROM Product A LEFT JOIN Sales B ON A.product_id = B.product_id
GROUP BY A.product_id
HAVING SUM(B.sale_date NOT BETWEEN '2019-01-01' AND '2019-03-31') = 0

summary

HAVING Sentences are usually associated with GROUP BY Statements are used in conjunction with , Used to filter by GROUP BY Statement returned recordset .

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