First, the common sql
show variables like 'character_set_client'; # query character set
show databases; # listed in the database alter on all servers
create database if not exists test; # Creating a database
drop database fk; # delete the database
show tables from test; # display a table in the database
use test;
create table tb_dept(
Id int primary key auto_increment, # orthopedic department number from the primary key growth
Name varchar (18), # department name
description varchar (100) # Description
);
show tables from test;
desc tb_dept; # View information table
show create table tb_dept;
use test;
Employees table #
create table tb_emp(
id int primary key auto_increment, # auto_increment just MySQL-specific
Name varchar(18),
sex varchar(2),
age int,
address varchar(200),
email varchar(100)
);
drop table tb_dept;
# Modify column type
# Note: Not all cases can go be modified,
# Can only be changed if the field only contains a null value.
alter table tb_emp modify sex varchar(4);
# Add column
alter table tb_emp add tel varchar(12);
# Remove Columns
alter table tb_emp drop tel;
alter table tb_emp drop column tel;
# Column renamed
alter table tb_emp change Name emp_Name varchar(18);
# Change the name of the table
alter table tb_emp rename emp;
rename table emp to tb_emp;
# Insert | delete | Update
insert into dept_emp (Name,sex,age,address,email)values('','','','','');
delete from tb_info where tmp_name = 'zxm';
update tb_info set tmp_name = 'zrr' where id = 13;
MySql run safe-updates the mode, which will lead to the non-primary key conditions can not perform update or delete command, execute the command SET SQL_SAFE_UPDATES = 0; modify the database schema
Two, mysql the top
When the function select top achieved starting in mysql: select * from tablename limit M, N
Where M represents the (M + 1) record start, N represents the number of records returned
select * from info order by no desc limit 0,5;
Three, MySQL5.7 type in the new JSON
1, native JSON advantages are as follows:
(1) similar to the text storage, can be saved a very large data.
(2) JSON validity check : data must be inserted JSON string type job.
(3) Compared to traditional forms, through all the strings do not need to find data.
(4) Support Index: through a virtual column can be indexed on the part of the data in JSON functions.
(5) JSON makes query performance
2, for a column is json, the need to use built-in functions json_extract ( column name , '$. Key') This function takes two parameters, the first parameter is the column name json column, the second parameter $. wherein the key is a key string json one key.
SELECT uid,json_extract(info,'$.mail') AS 'mail',json_extract(info,'$.name') AS 'name' FROM USER