MySQL (II) - MySQL data type

One 、INT type

type	byte	minimum value ( A signed / Unsigned )	Maximum ( A signed / Unsigned )
TINYINT	1	-128  /  0	127  /  255
SMALLINT	2	-32768  /  0	32767  /  65535
MEDIUMINT	3	-8388608  /  0	8388607  /  16777215
INT	4	-2147483648  /  0	2147483647  /  4294967295
BIGINT	8	-9223372036854775808  /  0	9223372036854775807  /  18446744073709551615

notes ： Usual use BIGINT Are signed .

1、 Create a table with unsigned fields 
    CREATE TABLE test_unsigned (a INT UNSIGNED,b INT UNSIGNED);
    insert into test_unsigned values(1,2);
    select a-b from test_unsigned; #  Due to the use of unsigned types ,a-b=-1, Beyond the int Type precision , So this SQL Report errors 

2、INT(N) What is it? ？
    create table test_int_n(a int(4) zerofill);
    insert into test_int_n values(1);
    insert into test_int_n values(123456);

    mysql> select * from test_int_n;
    +--------+
    | a      |
    +--------+
    |   0001 |
    | 123456 |
    +--------+
#######################
int(N) Medium  N  It's the display width ,  Does not mean   Stored digital   length   Upper limit .
zerofill  Represents when the stored number   length  < N  when , use   Numbers 0  Fill left , Until the full length  N
 When storing the length of a number   exceed N when  , according to   Actual storage   The digital display of 

3、 Self increasing 

 Are there any mistakes in the following grammar ？
 create table test_auto_increment(a int auto_increment); # error , Auto increment must be added to the primary key 
 create table test_auto_increment(a int auto_increment primary key);#  correct 

 following SQL What is the result of the operation ？
insert into test_auto_increment values(NULL); # 1
insert into test_auto_increment values(0);
insert into test_auto_increment values(-1); #-1
insert into test_auto_increment values(null),(100),(null),(10),(null);

#####
 If the insert value is 0 or null Is self increasing , If it is a negative number, you can insert .

  Two 、 Character

type	explain	N The meaning of	Whether there is a character set	Maximum length
CHAR(N)	Fixed length characters	character	yes	255
VARCHAR(N)	Variable length characters	character	yes	16384
BINARY(N)	Fixed length binary bytes	byte	no	255
VARBINARY(N)	Variable length binary bytes	byte	no	16384
TINYBLOB(N)	Binary big object	byte	no	256
BLOB(N)	Binary big object	byte	no	16K
MEDIUMBLOB(N)	Binary big object	byte	no	16M
LONGBLOB(N)	Binary big object	byte	no	4G
TINYTEXT(N)	Big object	byte	yes	256
TEXT(N)	Big object	byte	yes	16K
MEDIUMTEXT(N)	Big object	byte	yes	16M
LONGTEXT(N)	Big object	byte	yes	4G

1、 Sort rule ,bin Store every character in the string in binary data , Case sensitive ,cici Case insensitive ,ci by case insensitive Abbreviation , That is, the case is not sensitive ;
    select 'a' ='A';

    create table test_ci(a varchar(10),key(a));
    insert into test_ci values('a');
    insert into test_ci values('A');

    select * from test_ci where a = 'a';   -- What's the result ？

    set names utf8mb4 collate utf8mb4_bin
     
    select * from test_ci where a = 'a';   -- What's the result ？

  3、 ... and 、 The date type

The date type	Occupancy space	Scope of representation
DATETIME	8	1000-01-01 00:00:00 ~ 9999-12-31 23:59:59
DATE	3	1000-01-01 ~ 9999-12-31
TIMESTAMP	4	1970-01-01 00:00:00UTC ~ 2038-01-19 03:14:07UTC
YEAR	1	YEAR(2):1970-2070, YEAR(4):1901-2155
TIME	3	-838:59:59 ~ 838:59:59

notes ：datetime No time zone ,timestamp Time zone

create table test_time(a timestamp,b datetime);
insert into test_time values(now(),now());
select * from test_time;
set time_zone='+00:00';
select * from test_time;

Four 、json type

1、JSON Use of type  
    create table json_user (uid int auto_increment,data json,primary key(uid));
    insert into json_user values (null, '{"name":"li","age":18,"address":"beijing"}' );
    insert into json_user values (null,'{"name":"zhang","age":28,"mail":"[email protected]"}');

2、JSON Type dependent functions 
    json_extract： extract 
        select json_extract(data, '$.name'),json_extract(data, '$.address') from json_user;
        +------------------------------+---------------------------------+
        | json_extract(data, '$.name') | json_extract(data, '$.address') |
        +------------------------------+---------------------------------+
        | "li"                         | "beijing"                       |
        | "zhang"                      | NULL                            |
        +------------------------------+---------------------------------+

    JSON_OBJECT：  Convert object to json
        insert into json_user values ( null,json_object("name", "wangwu", "email", "[email protected]", "age",35) );

    json_insert：  insert data 
    json_merge：   Merge the data and return 
     Other functions ：https://dev.mysql.com/doc/refman/5.7/en/json-function-reference.html

3、JSON Index of type 
    JSON  Type data itself cannot be indexed directly , Need to index JSON Data regenerates virtual columns (Virtual Columns) after , Index the column .
     create table test_inex_1(
         data json,
         gen_col varchar(10) generated always as (json_extract(data, '$.name')), 
         index idx (gen_col) 
     );