Mysql database development specification

Table building related ：

1、 Create database character set selection utf8mb4, Sort set selection utf8mb4_general_ci; Build table 、 Index building 、 There is no need to specify a character set for operations such as adding fields , The default is the character set of the database .

Example ：create database [if not exists] dbname default character set UTF8MB4 default collate utf8mb4_general_ci;

2、 Library name 、 Table name 、 The field name cannot exceed 32 Characters . The number of fields in a single table should not exceed 50 individual , Big data wide table exception .

3、 Do not use complex data types ( Array , Customization, etc ); No use ENUM、SET type , Use TINYINT Instead of ;

4、 The field length depends on the actual business needs , Set the length as small as possible ;

5、 Each column must be defined with comments;

6、 The table must have a primary key , It is suggested to use snowflake algorithm to generate , The type is bigInt(19) unsigned;

7、 Precise floating-point data storage , Need to use DECIMAL, No use FLOAT and DOUBLE.

8、 Unified time storage timestamp （ Millisecond value ）, Field type is bigint(19);

9、 The amount is saved in the database to Fen , Field type is bigint(19);

10、 The number of characters in a line ( The total length of characters in each column ) May exceed 15000 At the upper limit , To consider the use of TEXT Type storage , Another suggestion is TEXT Split the field from the original table , Associated with the original table with a primary key .

11、 It is forbidden to store plaintext password in database , Encrypt the password and store it .

12、 Avoid using stored procedures 、 trigger 、EVENT.

13、 It is suggested that there are eight redundant fields in the main business table ：

`version` bigint(19) NOT NULL DEFAULT '0' COMMENT ' Version number , Optimism lock ',

`creator_id` bigint(19) NOT NULL DEFAULT '0' COMMENT ' founder ',

`creator_name` varchar(30) DEFAULT '' COMMENT ' Creator name ',

`create_time` bigint(19) NOT NULL DEFAULT '0' COMMENT ' Creation time ',

`modifier_id` bigint(19) NOT NULL DEFAULT '0' COMMENT ' Modifier ',

`modifier_name` varchar(30) DEFAULT '' COMMENT ' Name of modifier ',

`modify_time` bigint(19) NOT NULL DEFAULT '0' COMMENT ' Modification time ',

`is_deleted` tinyint(1) NOT NULL DEFAULT b'0' COMMENT ' Delete logo ',

Optimization ：

1、 No use select * The query .

2、 need join Field of , There must be an index on the field , And the data type is absolutely consistent , avoid Block Nested Loop And implicit transformation ;

3、 Try to avoid using unequal queries , for example ：NOT、!=、<>、!<、!>、NOT EXISTS、NOT IN、NOT LIKE etc. .

4、 For multi value matching of the same field in(), And pay attention to control IN The number of median values , Suggest less than 300 individual .

Example ：select id,name,deptname from emp where deptname in ('clerk','manager','sales');

5、 because GROUP BY It has the functions of grouping and automatic sorting , In the business logic scenario without sorting , Use Order by NULL Avoid sorting .

Example ：select ...from tab group by col1 order by null;

6、WHERE In the condition, there is no mathematical operation or function operation on the index column , If necessary, you can use related functions on some columns , But in Where It is strictly forbidden to use any function on the left of the predicate expression in Clause , Including data type conversion functions .

The wrong way to write :

select createtime

from .. .

where date_format(createtime, '%Y%m%d %H:%i:%s')= '20090101 00:00:0';

Correct writing :

select date_format(createtime, '%Y%m%d %H:%i:%s')

from .. .

where createtime =str_to_date('20090101 00:00:00', '%Y%m%d %H:%i:s');

7、 Do not use select And from Use subqueries , It is suggested to convert it into equivalent table associations in the scenario of using sub queries ;

Wrong writing ：

Select col1,(select col2 from b where b.id = a.bid) bcol2 from a where a.name=’xxxx’;

Write it correctly ：

Select a.col1,b.clo2 from a left join b on a.bid = b.id where a.name=’xxxx’;

Index related ：

1、 Naming rules ：

Primary key ：pk_ Table name ;

UNIQUE Indexes :uk_ Table name _ Field name ( Or field abbreviations );

Indexes ： Non unique cable idx_ Table name _ Field name ( Or field abbreviations );

Composite index ：idx_ Table name _ Field abbreviations , Take abbreviations that represent meaning as much as possible , Such as business_contract surface customerid and customername Index on ：idx_business_contract_cid_cname.

2、 Foreign keys are not allowed , But the associated field must have an index ;

3、 It is suggested that the number of indexes in a single table should be controlled at 5 Within a ;

4、 It is recommended that the number of fields in the index should not exceed 5 individual ;

5、 about where after and Multiple conditions for , Try to use combined index , It is forbidden to build an index for each condition .

6、 In the composite index , The column corresponding to the most frequently used equivalence condition is placed in front of the index , The column corresponding to the range condition is placed at the end of the index

7、 Try to put the column with small field length on the leftmost side of the composite index

8、 Avoid duplicate indexes 、 Redundant index , redundancy / Duplicate index

Duplicate index example ：primary key(id)、index(id)、unique index(id);

Examples of redundant indexes ：index(a,b,c)、index(a,b)、index(a);

Last , Good habits , Can reduce the 90% Of BUG