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Common SQL commands

2022-04-23 19:09:00 【Game programming】

Catalog

First choose database

USE DatabaseName;


About table	Code
establish table	create table xx();
Copy table	create table xx1 like xx;
change table name	rename table xx to xx2;

establish table Writing

CREATE TABLE lesson (
id int(11) NOT NULL AUTO_INCREMENT,
name varchar(32) default '',
views int(11) NOT NULL default '0',
created_at DATETIME,
PRIMARY KEY (id,name)
FOREIGN KEY () REFERENCES XX()
);


alter	code
Delete	ALTER TABLE xx DROP COLUMN c
increase	ALTER TABLE xx ADD COLUMN c a varchar(50)
renamed	ALTER TABLE xx CHANGE COLUMN c C
Change properties	ALTER TABLR xx CHANGE COLUMN c c age int()
increase primary key	ALTER TABLE xx ADD CONSTRAINT Constraint name PRIMARY KEY
Delete primary key	ALTER TABLE xx DROP primary key

to tablle Add data

Query data

duplicate problem

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	place table/column	column Data processing	Sort	Customize table	Data attribute
Code	where	avg,count	oder by(desc,asc	as	null
	in	like		some(select ...)	exist
	from	distinct xx/unique(select)		all(select..)
	with	having(group by)	group by
		between and

For select Must ignore null value

distinct & unique

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Choice problem

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Use where

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Use like

Use in To execute multi table queries

as Usage: multi table query

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some & as swap

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Use many = Do multi table query

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order by

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Set performance

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avg,count

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group by

having

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exits

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author ：DendenTaytay

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https://yzsam.com/2022/04/202204231906382002.html

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