Summary of database Simple query

Basic classification of query operations for databases:
1. Projection Operation 2. Select Action 3. Sort operations

Projection operation:

SELECT column list from table name;
SELECT * from table name; (Query entire table)
SELECT column name as new column name from table name; (Query column displays new column name)
SELECT DISTINCT column name from table name; (excluding duplicate data)
SELECT CONCAT (column name 1, '-', column Name 2, '-', column name 3) as ' title ' from table name; (String connection)
SELECT column name from table name limit start ordinal, return row number; (return qualified row query)

Select action:

SELECT column name from table name WHERE condition;
SELECT column name from table name WHERE condition and condition;
SELECT column name from table name WHERE condition or condition;
SELECT COUNT (*) as ' title ' from table name WHERE condition; (statistic satisfies the number of conditions)
SELECT column name from table name WHERE condition between upper and lower bounds;
SELECT * FROM table name WHERE age in (11,13,14); (Find the specified range)
SELECT * FROM table name WHERE age not In (11,13,14) (Find out in the specified range);

SELECT column name from table name WHERE condition like ' _% '; (Fuzzy query)
Escape character '%50p%% ' escape ' P ' or '%50<escape char>%% ' or '%50[%% '
Not the latter two escaped MySQL

SELECT column name from table name WHERE column Name 1 is not NULL; (Query test column name 1 not empty)
SELECT column name from table name WHERE column name 1 is null; (Query test column name 1 is empty)

Sort operations:

SELECT column name from table name ORDER by column name ASC (ascending);
SELECT column name from table name ORDER by column name DESC (descending);

Execution Order of SQL:
1.FROM 2.WHERE 3.SELECT 4.ORDER by

--standard structure of simple query statements
--Select Column1,column2,column3 from t_name where Column1 > ORDER by column1 ASC; --desc

-Drop database demo;
--Create DATABASE demo;
-Use demo;
/*
CREATE TABLE Student (
ID int primary KEY auto_increment,
' Name ' varchar (255) is not NULL,
Age int,
Gender char (2),
Address varchar (255) Default ' Chengdu City '
) Charset=utf8;
*/
/*
INSERT into student (name, age, gender) values
(' Zhang San ', 17, ' Male '),
(' John Doe ', 19, ' Male '),
(' Harry ', 23, ' female '),
(' Type builded with ', 22, ' Male '),
(' David ', 30, ' male '),
(' Heshasha ', 22, ' female '),
(' Wang Dan ', 20, ' female '),
(' Liu Tangyuan ', 24, ' Male '),
(' In the Ocean ', 15, ' Male '),
(' Nie Fengtao ', 39, ' Male ');
*/
--Select Id,name,age,gender from student where the age >18 order by Age,name,id;

--Select ID as ' number ', name as ' student name ', age as ' old ', gender as ' gender ' from student;

--Select Age+10 as ' ten years later ', name as ' name ' from student;

--Update student Set gender = ' female ' where id = 4;

--select distinct age,gender from student; --Filter duplicate data, use combination match when multiple columns

--Select CONCAT (Name, '-', gender, '-', age) as ' student information ' from student;

--Select ID, name, age, gender from student limit 5;

--Select ID, name, age, gender from student limit 4, 2;

--select * FROM student where name! = ' Zhang San ' or age > 18;

--select * from student where age between and 22;

--select * from student where Age in (15,18,22);

--select * from student where age is not in (15,22);

--INSERT into student (name, age, gender, address) VALUES (' Search ', 80, ' Male ', ' Chengdu [');

--Select id,name,address from the student where address like '%a%% ' escape ' a ';

SELECT * FROM student where gender is null;

SELECT * from student where name is not null;

Summary of database Simple query