mysql basic sql statement usage example

@mysql basic sql statement
DB DBMS SQL to
connect to the database

mysql-> mysql -h ip -uuser -ppassword
 use leaseback

Create table

CREATE TABLE test1 (
	id int(11) PRIMARY KEY,
	city VARCHAR(20) not null,
	count_person int(50)
);

Copy table field structure and index

CREATE TABLE test2 LIKE test1;

Copy table does not copy index can select fields

CREATE table test3 as SELECT id,city FROM test1;

Add column

ALTER TABLE test1 add COLUMN color VARCHAR(20);

Delete primary key

ALTER TABLE test1 DROP PRIMARY KEY;

Add primary key

alter TABLE test1 add PRIMARY KEY(id);

Add data to stored procedure

DROP PROCEDURE IF EXISTS proc_initData;
DELIMITER $
CREATE PROCEDURE proc_initData()
BEGIN
    DECLARE i INT DEFAULT 1;
    WHILE i<=3 DO
        
insert into t_user ( 
    userId,
    userName,
    password,
    phone)
 values (i,'ww','123456','135786');
    SET i = i+1;
    END WHILE;
END $

CALL proc_initData();

Stored procedure cycle add

delimiter $$     
create procedure pre()		
begin
declare i int;	
set i=1;
while i<21 do		
INSERT INTO test.test2(id,city,count_person,color) VALUES (i, CONCAT('西昌',i),CONCAT(220,i), 
  'blue');
set i=i+1;		
end while;
end 
$$
call pre();

Delete stored procedure method

drop procedure if exists pre;	

Add index

ALTER TABLE test1 add UNIQUE INDEX (city);

Show existing indexes

show INDEX from test1;

Delete index

ALTER TABLE test1 drop INDEX city;

Insert a piece of data

INSERT into test1 (id,city,count_person,color) VALUES (1,'成都',10000,'白色');

Query data in the table

SELECT * from test1;
SELECT * from test2;
SELECT * FROM test1 WHERE id<10;
SELECT * from test1 WHERE color LIKE '%白色%';

Sort forward and reverse

SELECT * FROM test1 ORDER BY count_person DESC;
SELECT * FROM test1 ORDER BY count_person ASC;

Built-in function

#总数
SELECT count(city) FROM test1;
#求和
SELECT SUM(count_person) as 'Total' from test1;
#求平均数
SELECT AVG(count_person) as avgperson from test1;
#求最大和最小
SELECT MAX(count_person) as maxperson FROM test1;
SELECT MIN(count_person) as minperson FROM test1;

UNION operator combines the other two result tables

SELECT color FROM test1 UNION ALL SELECT color FROM test2;
SELECT color FROM test1 UNION SELECT color FROM test2;

The EXCEPT operator returns what is in 1 but not in 2 is related to the order

SELECT color FROM test1 EXCEPT SELECT color FROM test2;

The intersect operator returns those records that have the same value in the selected columns of the two tables

SELECT color，city FROM test1 intersect SELECT color,city FROM test2;

Inner connection WHERE or on

SELECT * FROM test1,test2 WHERE test1.color=test2.color;
SELECT * FROM test1 INNER JOIN test2 on test1.color=test2.color;

Outer join the intersection of two tables (left outer join (including the data in the left table), right outer join (including the data in the right table))

SELECT * FROM test1 LEFT JOIN test2 ON test1.color=test2.color;
SELECT * FROM test1 LEFT JOIN test2 ON test1.color=test2.color and test1.count_person>2000;
SELECT * FROM test1 RIGHT JOIN test2 on test1.color=test2.color and test2.count_person>20000;
SELECT * FROM test1 RIGHT JOIN test2 on test1.color=test2.color WHERE test2.count_person>20000;

Fully connected

SELECT * FROM test1 FULL JOIN test2;

Group by

SELECT color FROM test1 Group by color;
SELECT color,count(id) AS sums FROM test1 GROUP BY color;
SELECT test1.color,count(test1.id) as sums FROM test1 LEFT JOIN test2 on test1.color=test2.color GROUP BY test1.color;

change the data

UPDATE test1 set color='pink' WHERE id BETWEEN 1 AND 5

Delete table

DROP TABLE test2;

There are three ways for sql to clear table data:
1. truncate-delete all data, retain the table structure, and cannot be undone to restore the
truncate table table name
2. delete-delete row by row is extremely slow, not suitable for large amounts of data delete
delete from table name
delete from table name where column name="value"
3. drop-delete table, delete data and table structure together, quickly
drop form table name