database DATABASE
MySql oracle port 3306
Oracle port 1521
Sqlserver port 1433
divided into
DDL defines the class statement such as building a table library and changing the table structure
DML operation class statement Data addition, deletion, modification, search, etc.
DCL Control Statement Privilege Control Transaction Control
DDL:
create database create database database name
delete library drop database library name
switch database use library name
create table create table table name (
column name column type,
column name column type
)
create table myuser(
hat int
uname VARCHAR(20),
sex varchar(2)
);
drop table drop table myuser;
Modify the table structure alter table myuser ADD age int;
DML manipulation data
add insert into table(column,column) values(value,value);
insert into myuser(uid,uname,sex,age) values(1,'小强','男',22);
delete delete from table where condition
delete from myuser where uid>=3;
delete from myuser where uname='张三丰' or uid=2 ;
change
update table set column=value, column=value where condition
update myuser set sex='女' ,age=18 where uid=3 and uname='张三丰'
check
select column,column,column from table where condition
* represents all columns
select * from myuser where age>18;
column type
Numerical
tinyint smallint int 整数 bigint
float double
character type
char 0~255 fixed-length characters
In name char(10) ______ exchange space for time
Insufficient right-hand padding spaces will be automatically removed when querying
varchar 0~65535 bytes If it is utf-8, a Chinese character is processed by 3 bytes, 21844 Chinese characters
Name varchar(9) occupies three bytes and uses time for space
text 65535 characters
longtext 4G
date type
datetime date time stores the year, month and day
timestamp date and time stored in seconds
Large field type to store some file xml text information
blob 65535 byte
longlob 4g
check sentence
where condition
l column=value and and or or > < >= <= != not equal to <> not equal to >< not true
l column in (value, value, value) The value of the column is one of the brackets
select * from myuser where age in (18,20,23,500)
l column between value and value 1 column value >= value and <= value 1
select * from myuser where age BETWEEN 19 and 499;
l Column like fuzzy query % any character _ any character
select * from myuser where uname like '%张%'
l Sort order by column asc ascending order (default) desc descending order is placed at the end of sql
select * from myuser order by uid desc ,age asc;