What are the SQL add / delete / modify queries?

SQL Can not do without adding, deleting, modifying and checking , Part of this article SQL It may not belong to “ Additions and deletions ” Range , therefore , This article only represents the personal idea that “ Additions and deletions ” To summarize

One 、 increase

database

• Create database

CREATE DATABASE  Database name ;

View

• Create a single table view

CREATE VIEW  View name  AS SELECT  Data table fields  FROM  Data table name ;

• Create a multi table view

CREATE VIEW  View name  AS SELECT  surface 1. Field , surface 2. Field  FROM  surface 1, surface 2 WHERE  Conditions ;

• Insert a piece of data

INSERT INTO  View name  VALUES ( Insert value );

• Insert multiple data

INSERT INTO  View name  ( Insert sub segment ) VALUES ( Insert value ),( Insert value );

Data sheet

• Create data table

CREATE TABLE  Table name (
	 Column name 1  data type ,
	 Column name 2  data type ,
	.......
);

• Add fields

ALTER TABLE  Table name   Field name   Field data type ;

• Insert a piece of data

INSERT INTO  Table name  VALUES ( Insert value );

• Insert the value of the corresponding field

INSERT INTO  Table name  ( Field ) VALUE ( Insert value );

• Insert multiple data

INSERT INTO  Table name  ( Field ) VALUES ( Insert value ),( Insert value );

Two 、 Delete

database

• Delete database

DROP DATABASE  Table name ;

View

• Delete data

DELETE FROM  View name  WHERE  Conditions ;

Data sheet

• Delete data table

DROP TABLE  Table name ;

• Delete field

ALTER TABLE  Table name  DROP COLUMN  Field name ;

• Delete data ( Remember to add WHERE Clause , nothing WHERE Clause is to delete all the data in the table by default )

DELETE FROM  Table name  WHERE  Conditions ;

• Delete table data

TRUNCATE TABLE  Table name ;

DROP、TRUNCATE、DELETE The difference between

3、 ... and 、 Change

database

• Modify the database name

ALTER DATABASE  Original name  MODIFY NAME =  New name ;

View

• Modify view fields

CREATE OR REPLACE VIEW  View name  AS SELECT * FROM  Data table name ;
 or 
ALTER VIEW  View name  AS SELECT * FROM  Data table name ;

• Modify view data

UPDATE  View name  SET  Fields that need to be modified  = ' Modified value ';

Data sheet

• Modify the name of the table

ALTER TABLE  Original table name  RENAME TO  The new name of the table ;

• Modify field name

ALTER TABLE  Table name  CHANGE  Original field name   new field name   New field data type ;

• Modify field data type

ALTER TABLE  Table name  ALTER COLUMN  Field   data type ;

• Modify the data of a field in the table , Multiple fields are separated by commas ( Remember to add WHERE Clause , nothing WHERE Clause is to modify all contents of the field by default )

UPDATE  Table name  SET  Field  = '' WHERE  Conditions ;

Four 、 check

database

• view the database

SHOW DATABASES;

View

• View view structure

DESC  View name ;
 or 
DESCRIBE  View name ;

• Check out the SQL sentence

SHOW CREATE VIEW  View ;

• View view

SELECT * FROM  View name ;
 or 
SHOW CREATE VIEW  View name ;
 or 
SHOW TABLE STATUS LIKE ' View name ';

Data sheet

• View table structure

DESC  Table name ;
 or 
DESCRIBE  Table name ;

• View the SQL sentence

SHOW CREATE TABLE  Table name ;

• View table data

SELECT * FROM  Table name ;

• View the specified field data

SELECT  Specify the field name  FROM  Table name ;

• View matching fields 1 Indexes （ Conditions ） The data of

SELECT * FROM  Table name  WHERE  Conditions ;

• View the matching fields 1、 Field 2 Indexes （ Conditions ） The data of , Intermediate use AND Connected to a

SELECT * FROM  Table name  WHERE  Conditions 1 AND  Conditions 2; 

• View matching fields 1、 Field 2 One of the indexes （ Conditions ） The data of , Intermediate use OR Connected to a

SELECT * FROM  The name of the table  WHERE  Conditions 1 OR  Conditions 2; 

• View matching fields 1 Indexes , And match the field 2、 Field 3 One of the indexes （ Conditions ） The data of , use AND While connecting, you should also OR Enclosed in brackets

SELECT * FROM  The name of the table  WHERE  Conditions 1 AND ( Conditions 2 OR  Conditions 3); 

• Internal connection （INNER ）JOIN

SELECT * FROM  surface 1, surface 2 WHERE  surface 1. Field  =  surface 2. Field 
 or 
SELECT * FROM  surface 1 JOIN  surface 2 ON  surface 1. Field  =  surface 2. Field 
 or 
SELECT * FROM  surface 1 INNER JOIN  surface 2 ON  surface 1. Field  =  surface 2. Field 
--  Use... For multiple conditions And Connected to a 
SELECT * FROM  surface 1 INNER JOIN  surface 2 ON  Conditions 1 AND  Conditions 2

• Left connection LEFT JOIN

SELECT * FROM  Table name 1 LEFT JOIN  Table name 2 ON  Connection condition （ Multi conditional use AND or OR Connect ）

• The right connection RIGHT JOIN

SELECT * FROM  Table name 1 RIGHT JOIN  Table name 2 ON  Connection condition （ Multi conditional use AND or OR Connect ）

• Group query GROUP BY

SELECT * FROM  Table name  GROUP BY  Group query fields ;

• Group query Filter grouping data GROUP BY + HAVING

SELECT * FROM  Table name  GROUP BY TIME HAVING  Field  = '';

• Group query , Get the grouped set GROUP BY + GROUP_CONCAT

SELECT GROUP_CONCAT( Fields that require a collection ) FROM images GROUP BY  Grouped fields ;

• Ascending query ASC

SELECT * FROM  Table name  ORDER BY  Fields for ascending query  ASC;

• Descending query DESC

SELECT * FROM  Table name  ORDER BY  Fields queried in descending order  DESC;

• The query returns the specified number LIMIT

SELECT * FROM  Table name  LIMIT  Limit the number of returned entries ;
 or 
SELECT * FROM  Table name  LIMIT  Limit the number of returned entries , To which article ;

• Fuzzy query LIKE

SELECT * FROM  Table name  WHERE  Field  LIKE '% value %';

• nested queries

SELECT * FROM  Table name 1 WHERE  Table name 1 Field  = (SELECT  Table name 2 Field  FROM  Table name 2 WHERE  Conditions );

Function query

Aggregate functions

• Query average AVG

SELECT AVG( Field ) FROM  Table name ;

• Number of query table rows COUNT

SELECT COUNT(*) FROM  Table name ;

• Query maximum MAX

SELECT MAX( Field ) FROM  Table name ;

• Query minimum MIN

SELECT MIN( Field ) FROM  Table name ;

• Sum up SUM

SELECT SUM( Field ) FROM  Table name ;

Date function

• Query the current date

-- MySQL usage ：
SELECT NOW();
-- SQL Server usage :
SELECT GETDATE();

• Query the difference between dates

-- MYSQL usage :
SELECT DATEDIFF( date 1, date 2);
-- SQL Server
--  The return format can be year 、 quarter 、 month 、 Day, etc. , For details, please refer to ：https://www.w3school.com.cn/sql/func_datediff.asp
SELECT DATEDIFF( Returns the format , date 1, date 2);

• Query the specified date year

--  result ：2021
SELECT YEAR('2021-05-01');

• Query the specified date and month

--  result ：5
SELECT MONTH('2021-05-01');

• Query the specified date and days

--  result ：1
SELECT DAY('2021-05-01');

• Query the day of the week when a date is

--  result ：4
SELECT DAYOFWEEK('2021-04-28'); 

Summary ：
1、 Data table and view are related , When the view （ Data sheet ） Data deletion , Corresponding data sheet （ View ） Data will also be deleted .
2、 About functions , Only a few are listed here , And string functions 、 System function 、 There was no introduction to mathematical functions , If you are interested, you can find out by yourself .
High EQ ： These are just what I know SQL The tip of the iceberg , It's just a simple use , complex SQL I seldom use it .
Low EQ ： That's all I know ！