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What is MySQL? What is the learning path of MySQL
2022-07-06 09:02:00 【Automated test seventh uncle】
Preface
Today, I want to tell you about MySql, This article is divided into two parts , Namely mysql Basic part and advanced part , I won't say more nonsense , Let's go straight to the topic .
One . Basics
1.1 Database operation
Show databases; Show all databases
Show tables; Show all database tables
Use databasename; Switch database
Desc tablename; Display all field information in the table
explain : Used in notes sql Statements use tables websites and access_log
surface 1:websites
+----+--------------+---------------------------+-------+---------+
| id | name | url | alexa | country |
+----+--------------+---------------------------+-------+---------+
| 1 | Google | https://www.google.cm/ | 1 | USA |
| 2 | TaoBao | https://www.taobao.com/ | 13 | CN |
| 3 | Novice tutorial | http://www.runoob.com/ | 4689 | CN |
| 4 | Microblogging | http://weibo.com/ | 20 | CN |
| 5 | Facebook | https://www.facebook.com/ | 3 | USA |
| 7 | stackoverflow | http://stackoverflow.com/ | 0 | IND |
+----+---------------+---------------------------+-------+---------+
surface 2:access_log
+-----+---------+-------+------------+
| aid | site_id | count | date |
+-----+---------+-------+------------+
| 1 | 1 | 45 | 2022-5-10|
| 2 | 3 | 100 | 2022-05-13|
| 3 | 1 | 230 | 2022-05-14 |
| 4 | 2 | 10 | 2022-05-14 |
| 5 | 5 | 205 | 2022-05-14 |
| 6 | 4 | 13 | 2022-05-15 |
| 7 | 3 | 220 | 2022-05-15 |
| 8 | 5 | 545 | 2022-05-16 |
| 9 | 3 | 201 | 2022-05-17 |
+-----+---------+-------+------------+
1.2 LIKE The operator
example :
select * from websites where url like 'https%';-- url contain https The data of
select * from websites where name like 'G%'; -- name With G start
select * from websites where url like '%h%';-- url contain h Field data of
select * from websites where name like '_o%';-- name in o Data in the second character
1.3ORDER BY keyword
explain : Sort the result set by one or more columns
example :
select name,alexa from websites
order by alexa desc; -- The default time is ascending desc Representation of descending order
select * from websites
order by country, alexa; -- In multi column sorting , First row country In the platoon alexa
1.4 INSERT INTO
explain : Insert data into table
example :
insert into websites
values (6,' Baidu ','http://www.baidu.com',22,'ZG');-- Columns can be omitted , But to insert all values
insert into websites (id ,name,url,alexa,country)
values ('7',' NetEase ','www.wangyi.com','25','ZG');-- You can specify which column to insert
1.5 UPDATE
explain : Update the data in the table
example :
update websites
set url = 'http://www.wangyi.com'
where id = 7;
update websites
set alexa = 5000, country = 'USA'
where id = 3;
1.6 DISTINCT
explain : Filter duplicate data
example :
SELECT DISTINCT country FROM Websites;
1.7 DELETE
explain : Delete data or delete tables
example :
-- Delete a row of data
SELECT FROM WEBSITES
WHERE ID = 7;
-- Delete the entire table , But the structure of the table still exists
SELECT FROM WEBSITES;
1.8 AND, OR ,IN
explain : Are used to filter data
example :
SELECT * FROM WEBSITES
WHERE ID BETWEEN 1 AND 3;
SELECT * FROM WEBSITES
WHERE ID = 1 OR ID =3;-- Screening id by 1 and 3 The data of
SELECT * FROM WEBSITES
WHERE ID IN (1,3);
That's all Mysql The basic part of , Some simple operations of adding, deleting, modifying and querying , Maybe the content is not very complete , But I hope for beginners Mysql Students can play a certain reference and reference role , Next, I will talk about the database building that should be included in the basic part , Table building, etc .. These are added to the advanced part by me .
Two 、 senior
2.1 CREATE DATABASE Building database
CREATE DATABASE BOKEYUAN;-- Create a name for BOKEYUAN The database of
2.2 CREATE TABLE Build table
USE BOKEYUAN;-- Use the newly created database
CREATE TABLE MYTABLE -- Create a name for MYTABLE Table of
(
ID INT(4) PRIMARY KEY COMMENT ' Serial number - The only key ' ,
NAME VARCHAR(255) NOT NULL COMMENT ' Website name ',
URL VARCHAR(255) UNIQUE COMMENT ' website ',
ALEXA INT(5) COMMENT ' Traffic volume ',
COUNTRY CHAR(20) COMMENT ' The country of the website '
);
2.3 INSER INTO SELECT
explain : We have created the table structure above , But the data has not been inserted yet , Then the basic part of the previous section has written about inserting data SQL sentence , In this part, we use another method to insert data , It is actually copying data from other tables
example 1: hypothesis MYTABLE Table does not exist , We can use the following method to copy the structure and data of other tables ( Because we use the same table data , So I will consider this method , If you are a new table, you can only create a table first and then insert data )
-- Suppose our websites Table in MYDATABASE In the database
CREATE TABLE MYTABLE SELECT * FROM MYDATABASE.WEBSITES;
example 2: We need a watch MYTABLE Already exist , Then the above table has been established , Then we can use INSERT INTO SELECT Statement to insert data directly ( Here is also a copy websites Data in )
INSERT INTO MYTABLE SELECT * FROM MYDATABASE.WEBSITES;
example 3: Insert a column of data
-- Insert only one column of data
INSERT INTO MYTABLE(NAME)
SELECT NAME FROM MYDATABASE.WEBSITES;
2.4 LIMIT
explain : Return record line , above SQL After execution, we will generate the following data table
# ID, NAME, URL, ALEXA, COUNTRY
'1', 'Google', 'https://www.google.cm/', '1', 'USA'
'2', ' TaoBao ', 'https://www.taobao.com/', '13', 'CN'
'3', ' Novice tutorial ', 'http://www.runoob.com/', '5000', 'USA'
'4', ' Microblogging ', 'http://weibo.com/', '20', 'CN'
'5', 'Facebook', 'https://www.facebook.com/', '3', 'USA'
'6', ' Baidu ', 'http://www.baidu.com', '22', 'ZG'
example 1:
-- Before acquisition 3 Row data 2 SELECT * FROM MYTABLE LIMIT 3;
-- obtain 3,4,5 Row data
SELECT * FROM MYTABLE LIMIT 2,3;
2.5 BETWEEN AND
explain : coordination WHERE Query condition statements used , Here is 3 Implementation acquisition 1 To 3 Method of row data , But in general, examples 1 It's more convenient , It's logical , And simple and easy to understand
example :
-- obtain 1 To 3 Row data
SELECT * FROM MYTABLE WHERE ID BETWEEN 1 AND 3;
example 2:
-- obtain 1 To 3 Row data can also be WHERE IN To achieve
SELECT * FROM MYTABLE WHERE ID IN (1,2,3);
example 3:
-- obtain 1 To 3 Another implementation of row data
SELECT * FROM MYTABLE WHERE ID < 4;
2.6 AS The operator
explain : Give column , Table alias
example 1:
-- Alias a column
SELECT NAME AS ' name ', URL AS ' website ' FROM MYTABLE;
example 2:
-- Merge 2 Columns , names need CONCAT keyword
SELECT NAME AS ' name ', CONCAT(URL,COUNTRY) AS ' Website country ' FROM MYTABLE;
example 3:
-- Aliasing tables , You can use aliases to access field elements
SELECT M.ID,M.NAME,M.COUNTRY FROOM MYTABLE AS M;
2.7 JOIN
explain : Connect two tables , Split left connection , Right connection and full connection , Here we need another table , Suppose the table is ACCESS_LOG, The structure is as follows :
# aid, site_id, count, date
'1', '1', '45', '2016-05-10'
'2', '3', '100', '2016-05-13'
'3', '1', '230', '2016-05-14'
'4', '2', '10', '2016-05-14'
'5', '5', '205', '2016-05-14'
'6', '4', '13', '2016-05-15'
'7', '3', '220', '2016-05-15'
'8', '5', '545', '2016-05-16'
'9', '3', '201', '2016-05-17'
example 1:
-- INNER JOIN Here we put MYTABLE Look at the left table ACCESS_LOG It's the right table , Below sql Statement will return the line that meets the condition , It can be imagined as the intersection of two sets in a set
SELECT M.*,A.SITE_ID FROM MYTABLE AS M
INNER JOIN ACCESS_LOG AS A
ON M.ID = A.SITE_ID
ORDER BY M.ID;
example 2:
-- Left connection , All rows of the left table will be returned , If there is no match, it will also return
SELECT M.* FROM MYTABLE AS M
LEFT JOIN ACCESS_LOG AS A
ON M.ID = A.SITE_ID
ORDER BY M.ID;
example 3:
-- The right connection , Return the rows of all right tables that meet the conditions
SELECT * FROM MYTABLE AS M
RIGHT JOIN ACCESS_LOG AS A
ON M.ID = A.SITE_ID
ORDER BY A.SITE_ID;
example 4:
-- Full connection
SELECT M.name, A.count, A.date
FROM MYTABLE AS M
FULL OUTER JOIN access_log
ON M.id=A.site_id
ORDER BY A.count DESC;
2.8 UNION
explain : The operator is used to merge two or more SELECT The result set of the statement . Be careful ,UNION Everyone inside SELECT Statements must have the same number of columns . Columns must also have similar data types . meanwhile , Every SELECT The order of the columns in the statement must be the same .
Hypothetical existence table MYSOFTW
# id, soft_name, url, country
'1', 'QQ APP', 'http://im.qq.com/', 'CN'
'2', ' Microblogging APP', 'http://weibo.com/', 'CN'
'3', ' TaoBao APP', 'https://www.taobao.com/', 'CN'
example 1:
-- Screening all countries , Do not include duplicate data
SELECT M.COUNTRY FROM MYTABLE AS M
UNION
SELECT W.COUNTRY FROM MYSOFTW AS W;
example 2:
-- The query country is “cn” All websites and software
SELECT M.URL ,W.COUNTRY FROM MYTABLE AS W
WHERE M.COUNTRY = 'CN'
UNION
SELECT S.APP_NAME,A.COUNTRY FROM MYSOFTW AS S
WHERE S.COUNTRY = 'CN';
summary
Today's content is a little more , But the feeling is still quite simple , As the saying goes, who makes perfect , Do more, write more, practice more , All in front SQL Statements are relatively simple , Because there is no practical significance , Just to learn , At work SQL Statements are more complex , A complex SQL Statements are simply a combination of several statements , As long as you comb your thoughts carefully .
I hope this article can help you , Favorite friends can like collection comments and pay attention , Of course, I also prepare a teaching video about database for you , Friends in need can privately send keywords “ Information ” Get it .
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