Summary for May 8

basic data type

1 Integer:

1 tinyint             2 int    3bigint

create table t1 (x int(5) unsigned zerofill)

The number after the int refers to the display width, not the storage limit

View sql mode show variables like '%mode%';

floating point

float  double decimal

create table t2(x float(5,3)) represents a total of 5 digits, two integers and 3 decimals

Precision float double decimal is getting higher and higher

character type

char fixed length

varchar variable length

create table t3(s char(4)) The number of character units is limited, and the insufficient ones are filled with spaces

create table t4(s char(4)) exceeds the error, there are several stored

select char_length(x) from t3; check character length

char disadvantage: waste of space

A bit: fast access

 

Date type:

data ：1990-09-20

time：10：30:20

datetime：1990-09-20 10：30:20

year：2000

Enumeration and Collection Types

enumeration enum select one

Collection set multiple selection multiple

create table t1 (s enum('play','read'))

create table t2 (s set('play','read'))

insert into t2 ('play,read')

insert into t1 ('play')