Niuke MySQL - SQL must know and know

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Today's series is ：MYsql——SQL Will know

Retrieving data

The first 1 topic

Existing table Customers as follows ：

cust_id
A
B
C

【 problem 】

To write SQL sentence , from Customers Retrieve all... From the table cust_id

select cust_id from Customers

The first 2 topic

surface OrderItems Contains non empty Columns prod_id On behalf of goods id, Includes all ordered items （ Some have been ordered many times ）.

prod_id
a1
a2
a3
a4
a5
a6
a7

【 problem 】 To write SQL sentence , Retrieve and list all ordered items （prod_id） The list after weight removal .

select  distinct prod_id  from OrderItems

The first 3 topic

Now there is Customers surface （ The table contains columns cust_id On behalf of the customer id,cust_name Name of representative client ）

cust_id	cust_name
a1	andy
a2	ben
a3	tony
a4	tom
a5	an
a6	lee
a7	hex

【 problem 】 You need to write SQL sentence , Retrieve all columns .

select  cust_id,cust_name from Customers

Sorting and retrieving data

The first 1 topic

Have a watch Customers,cust_id On behalf of the customer id,cust_name Name of representative client .

cust_id	cust_name
a1	andy
a2	ben
a3	tony
a4	tom
a5	an
a6	lee
a7	hex

【 problem 】 from Customers Retrieve all customer names in （cust_name）, And press from Z To A Display the results in the order of .

select cust_name from Customers order by cust_name desc

The first 2 topic

Yes Orders surface

cust_id	order_num	order_date
andy	aaaa	2021-01-01 00:00:00
andy	bbbb	2021-01-01 12:00:00
bob	cccc	2021-01-10 12:00:00
dick	dddd	2021-01-11 00:00:00

【 problem 】 To write SQL sentence , from Orders In the customer search table ID（cust_id） And order number （order_num）, And first press the customer ID Sort results , Then arrange the order date in reverse order .

select 
cust_id,order_num
from Orders 
order by cust_id asc,order_date desc

The first 3 topic

Let's say I have a OrderItems surface

quantity	item_price
1	100
10	1003
2	500

【 problem 】

To write SQL sentence , Show OrderItems The quantity in the table （quantity） And the price （item_price）, And according to the quantity from more to less 、 Prices are ranked from high to low .

select quantity,item_price from OrderItems order by quantity desc,item_price desc

The first 4 topic

Yes Vendors surface

vend_name
haidilao
Xiaolongkan
Big dragon

【 problem 】 Below SQL Is there a problem with the statement ？ Try to change it to correct , Make it work correctly , And return the result according to vend_name In reverse order

SELECT vend_name, 
FROM Vendors 
ORDER vend_name DESC;

right key

SELECT vend_name FROM Vendors ORDER by vend_name DESC;

Filtering data

The first 1 topic

Have a watch Products

prod_id	prod_name	prod_price
a0018	sockets	9.49
a0019	iphone13	600
b0018	gucci t-shirts	1000

【 problem 】 from Products Retrieve products from the table ID（prod_id） Product name （prod_name）, Only return the price of 9.49 Dollar products .

【 Sample results 】 return prod_id and prod_name

select prod_id,prod_name from Products where prod_price=9.49

The first 2 topic

Products surface

prod_id	prod_name	prod_price
a0018	sockets	9.49
a0019	iphone13	600
b0019	gucci t-shirts	1000

【 problem 】 To write SQL sentence , from Products Retrieve products from the table ID（prod_id） Product name （prod_name）, Only return the price of 9 Products of US dollars or higher .

【 Example answer 】 return prod_id goods id and prod_name Name of commodity

select prod_id,prod_name from Products where prod_price>=9

The first 3 topic

Yes Products surface

prod_id	prod_name	prod_price
a0011	egg	3
a0019	sockets	4
b0019	coffee	15

【 problem 】 To write SQL sentence , return Products All the prices in the table are at 3 Dollar to 6 The name of the product between US dollars （prod_name） And the price （prod_price）, Then sort the results by price

【 Sample results 】 Return the product name prod_name And commodity prices prod_price

select 
prod_name,
prod_price
from  Products
where prod_price between 3 and 6
order by  prod_price asc

The first 4 topic

OrderItems The table contains ： The order number order_num,quantity Product quantity

order_num	quantity
a1	105
a2	1100
a2	200
a4	1121
a5	10
a2	19
a7	5

【 problem 】 from OrderItems Retrieve all different and non duplicate order numbers in the table （order_num）, Each order must contain 100 One or more products .

【 Sample results 】 Return order number column order_num

select 
 distinct order_num
from OrderItems
where quantity>=100

Come on together