1064 means syntax error
create database dsay00; create database
create database day00 character set urf8 ; create database specified character set urf8
create database day00 character set utf8 collate utf8_bin; create database specified character set and check rules
show databases; show all databases
show database day00;Display database information
show character set;Display the character set supported by MySQL gbk urf8;
show create database day00 ;Display the character set for creating the database
show collation like 'utf8%';Display the validation rules under the specified character set
use day00 ; enter/switch the corresponding database
drop database day00; delete the database
alter database day00 character set 'gbk'; modify the character set of the
database alter database day00 collate gbk_bin; modify the validation rules
select database(); get the database currently in use
show tables ; show all tables
show create table stu; view the created table
desc stu; show the details of a table
Create table
create table data table name (
column name column type [constraint],
column name column type,
column name column type
);
create table stu(
name varchar(size),
age int,
num int,
birthday date
);
MySQL data types
Numeric type
tinyint
smallint
MEDIUMINT
int (most common)
bigint
time and date type
column type
'zero' value
DATETIME
'0000-00-00 00:00:00'
DATE
'0000-00-00'
TIMESTAMP (timestamp)
000000000000000
TIME
'00:00:00'
time and timestamp Difference:
date: only contains date, if no value is specified when incoming data, it will be null
timestamp: contains date and time, if no value is specified when incoming data, it will be the current system time
string type
char and The length of a varchar type
CHAR column is fixed to the length declared when the table is created. The length can be any value from 0 to 255. The value
in a VARCHAR column is a variable-length string. The length can be specified as a value between 0 and 65,535
char(character) fixed length, for example, the specified length is 100, the actual incoming value is 20, and the rest of the characters are filled with spaces.
varchar(variable character) variable length, for example: the specified length is 100 , the actual incoming value is 20. The actual storage is 20 characters
create table stu2(
name char(20),
age int,
birthday date,
login timestamp,
time time
);
insert into stu2 values('tom',10,'1998-10-10',null,'12:30:50');//Insert data
select * from stu;//Query data
Constraint
not null Non-null constraint
unique Unique (but null value is not equal to null value)
unique not null Unique non-null
primary key Primary key constraint (non-null and unique) auto_increment Automatic growth
create table employee(
id int primary key auto_increment,
name varchar(10) not null,
phone_num varchar(15) unique
); delete table drop table temp
for table operation ; modify table add column alter table employee2 add hobby varchar(20); delete column alter table employee2 drop hobby; modify the length of column alter table employee2 modify name varchar(20); modify the data type of the column alter table employee2 modify name int; modify the name of the column alter table employee2
change name score int;
rename table name
1. rename table employee2 to emp;
2. alter table employee2
rename to tmp; insert delect update select insert data insert into table name (column name 1, column name 2... ) values(value1, value2...); insert into employee2(id,name) values(1,'kk'); insert into employee2(id,name,phone_num) values(02,'kk','1516666666 '); //Generally id column does not need to pass values insert into employee2 values(null,'xx','13945551544',1000); insert into employee2 values(null,'Zhang San','132884884',5000); insert into employee2 values(null,'Zhang Sansi','185445284',200); insert into employee2 values(null,'Li Zhang Wangfei','1355444524',100);
insert into employee2 values(null,'Zhang Changzhang','11528452874',220);
insert into employee2 values(null,'Li Li','195554525278',1200);
delete data
delect from employee2 where id =2;
delect from employee2;Empty the table, keep the table structure (delete one by one)
truncate employee2;Empty the table, keep the table structure (delete the table at one time, equivalent to drop table, then create the same new empty table)
modify the data
update employee2 set name = ' ss' where id = 2;
update employee2 set salary= salary+100 where id = 3;
query data
select column name from table name where condition;
select * from employee2;
select name from employee2 where id>2;
select name,phone_num from employee2 where id>2;
//Query to remove duplicate distinct
select distinct salary from employee2;
//The column after the query is operated
select salary+100 from employee2;
//After the query, take the alias as (as can be omitted)
select salary+100 as new_salary from employee2;
Chinese garbled problem
Client server
cmd --> client -->server
1. Temporarily set cmd code
mysql --dafault-character-set=gbk -uroot -proot
will be invalid after the window is closed
2. Permanently set
modify the configuration file my.ini line 57 utf8 to GBK
restart mysql net stop mysql
net start mysql
common symbols
> < = <> !=
in(10,20,30)
like 'Zhang%' // %One or more characters
like '%Zhang'
like '%Zhang%' //As long as it includes Zhang
like 'Zhang_' // Only one wildcard can be matched
is null //judging empty
is not null //judging not empty
not
and
or
select* from stu where name = 'Li Si';
select * from employee2 where salary in(1000,200,1200);
select * from employee2 where name like 'Zhang%';
select * from employee2 where name like '__'; //Two underscores represent two words
select * from employee2 where name is null;
select * from employee2 where salary between 81 and 90;
select * from employee2 where salary 1000 or 2000;
sort
order by
asc ascending order (default)
desc descending order
select name,math,english from stu order by math asc,english desc;
select name,math+english as sum from stu order by sum desc;alias+sort sort
the English grades of all students surnamed Zhang in descending order
select * from stu where name like 'Zhang%' order by english desc ;
//Create student table
create table stu(
id int primary key auto_increment,
name varchar(10) not null,
age varchar(15) unique ,
math int,
english int
);
insert into stu values(null,'Li Hua', '15',60,30);
insert into stu values(null,'Li Ming','14',80,60);
insert into stu values(null,'Zhang Shi','22',40,96);
insert into stu values(null,' Wangwu','54',66,50);
insert into stu values(null,'angel','25',25,70);
insert into stu values(null,'devil','12',90, 52);
insert into stu values(null,'Li Si','31',98,90);
Aggregate function, usually used with grouping
count() count
count(*)
select count(name) from stu;
select count (*) as count from stu;//The query record is aliased
select count(*) as count from stu where math>80;
select count(*) as count as sum from stu where sum>120;
sum
sum()
select sum(math) as sum from stu;
select sum(math) ,sum(english) from stu;
if the aggregate function sum() is used, null is treated as 0;
select sum(math)+sum(english) from stu;
when there is a null value in a column in the record, if you use + to add, it will be null;
select sum(math+english) from stu;
solution: use ifnull(column name , specify the default value) function to solve the problem of adding to 0
select sum(ifnull(math,0)+ifnull(english,0)) from stu;
average
avg()
select avg(math) from stu;
求max() min()
select max(math) from stu;
select min(english) from stu;
//Create sales record table
create table orders(
id int primary key auto_increment,
product varchar(12) not null,
date timestamp,
price int
);
insert into orders values(null,'washing machine',null,1000);
insert into orders values(null,'TV',null,2200);
insert into orders values(null,'TV',null,2200);
insert into orders values(null,'washing machine',null,1000);
insert into orders values( null,'air conditioner',null,5000);
insert into orders values(null,'washing machine',null,1000);
insert into orders values(null,'air conditioner',null,5000);
insert into orders values(null, 'TV', null, 2200);
grouping operation group by
group by having followed by conditions // filter the results after group by again, cannot use where with having
select * from 表名 where 条件 group by 列名 having分组后的条件 order by 列名desc/asc；
select product, sum(price) from orders group by product;
select product, sum(price) from orders where price>1000 group by product having sum(price) >10000;
//出错，应该加别名 select product, sum(price) from orders where price>1000 group by product having sum >10000;
select product, sum(price) as sum from orders where price>1000 group by product having sum >10000;
select product, sum(price) as sum from orders where price>1000 group by product having sum >10000 order by sum desc;