############### CRUD operation in MySql####################
show create database tedu;
create database db2 charset utf8;
show create database db2;
#Create person table
use db2;
create table person(
name varchar(50),
age int
) charset utf8;
/* Insert data (full table insert) */
-- The order of insertion should be consistent
-- The type of insertion should be consistent
-- integers can be passed in as string types, but must be strings composed of pure numbers
-- if you determine the inserted value, you can use null
select * from person;
insert into person
values ('Zhang San', 34);
insert into person
values ('Liu Bei',null);
/* specify fingertip to insert records*/
insert into person(name) values ('Tom');
insert into person(name, age) values ('Luo Youquan' ,30); -- It is recommended to list the fields in the table in order
/* Full table insert multi-table records*/
insert into person values('Dafei',21),
('Erfei',18),
('Three Fei',16);
insert into person(name) values (' Villa'),('jack'),('lossi');
#person Insert record--
if the insertion string contains single quotes, you can use two single quotes to convert it into a single quote--
single quotes can prevent SQL injection
create table user(
username varchar(50),
password varchar(50)
)charset utf8;
insert into user(username, password) values ('Zhang Zhang','234134'),('Li Xiaofeng','adfc') ,('Liu Zilong','fadfsdg'),('Wang Dafei','5464re');
select * from user where username='Li Xiaofeng' and password='adfc';
#but input username:xxxx 密码： 1' OR '1'='1
select * from user where username='xxxx' and password='1' OR '1'='1';
* Modify data*/
select * from person;
update person set age=45 where name='Liu Bei';
update person set name='Guan Yu',age=42 where name='Tom';
/* delete data*/
delete from person where name=' lossi';
delete from person where age<20;
/* data type*/
-- value, date, string
-- value type tinyint smallint int[commonly used] bigint float doubl[commonly used] decimal(m,n)[commonly used]
drop table tb1;
create table tb1(
a tinyint,
b smallint,
c int,
d bigint(4), -- specify the display width, you can not specify
e float,
f double,
f1 double(6,4), -- also Can be displayed like decimal, but not strict, generally do not write
g decimal(6,4) -- strictly control the number of digits
)
insert into tb1(f1) values (22.33344);
insert into tb1(g) values (22.33344);
insert into tb1(f1) values (222.33344);
insert into tb1(g) values (222.33344);
select * from tb1;
/* String type
fixed-length character string, up to 255, if the insertion length is insufficient, it will be automatically filled, if it exceeds Assignment failed,
variable length string varchar; length must be specified;
-- char is more efficient than varchar;
text; 65535 bytes;
*/
/* date type
timestamp timestamp, will automatically record the inserted time
YY-MM- DD
HH:mm:SS
*/
create table tb3(
a time,
b date,
c datetime,
d timestamp
);
select * from tb3;
insert into tb3(a) values (' 21:51:00');
update tb3 set b='2023-06-11' where a='21:51: 00';