MySQL development specification pdf

Prohibited items :

1、 No use select * Etc

When querying all fields (select *) Can cause the following problems 1. Increase network bandwidth consumption 2. Select * It will inevitably lead to back table query / Return the data , Invalidate the overlay index

3. If the table structure is modified, such as adding multiple columns , It is dangerous to return redundant data

2、 Database name is prohibited 、 Table name 、 The field name uses MySQL Reserved words

When the name of the library 、 Table name 、 When properties such as field name contain reserved words ,SQL Statement must refer to the property name with backquotes , This will make SQL Statement writing 、SHELL Escape of variables in scripts 、 It becomes very complicated to modify the table structure online .

3、 The use of partitioned tables is prohibited Mysql Partition table technology is still not very mature , And there are strict requirements for partitioning keys , After the partition table becomes larger, it is very difficult for table backup and recovery , It is recommended to use... On the business side sharding technology .

4、 It is forbidden to store plaintext password in database If you need to store MySQL The password can be used MySQL Built in functions password() Clear text password MD5 To encrypt .

5、SQL It is forbidden to appear in now()、rand()、sysdate()、current_user() Waiting for uncertain results function .

It is suggested that the uncertain time should be taken out at the program layer , Statement level replication scenario , Cause inconsistency between master and slave data ; Functions of uncertain values , produce Of SQL The statement cannot be used .

6、 No use VARBINARY、BLOB Store image 、 Documents, etc. , Use VARCHAR(N),N all The quantity may be small

7、 Prohibit operations on columns An operation on a column will result in Mysql Full table scan due to index failure .

Specification item :1、 Create table character set using UTF8 perhaps UTF8mb4

UTF8 Unified and universal , There will be no risk of transcoding . If there is a need for emoticons , have access to utf8mb4

2、 The table must have a primary key , Recommended UNSIGNED Autoincrement column as primary key

Table has no primary key ,INNODB Hidden primary key columns will be set by default ; Tables without primary keys are very inefficient in locating data rows and reduce the efficiency of row based replication . When creating a table, you must define a self incrementing column as the primary key ( Nothing to do with business logic , If the application data has a unique candidate column, it can be made into a unique key ), Reiterated INNODB Each table in the storage engine must have a business independent auto increment column as the primary key .

Another suggestion :

1、 It is recommended to use prefix matching fuzzy queries cautiously

Prefix matching can lead to direct full table scan or full index scan , The worst performance , No extensions , Basically unacceptable .

2、 It is recommended that all fields be defined as NOT NULL, Set up default value .

Defined as Not Null Here's why :

1. MySQL Each in the database is NULL All of the columns need extra 1 Bytes for storage , Waste space resources .
2. B Tree indexes are not stored NULL value , If the index field can be NULL, Indexing efficiency will decrease .
3. Suggest using 0、 Special value or empty string instead of NULL value .

3、 It is recommended to avoid implicit conversion in queries MySQL If the query field is different from the table definition field, an implicit conversion will occur , Thus, the index cannot be used, resulting in low query efficiency .

4、 It is recommended not to MySQL Store business logic in the database .

Databases are stateful services , Changes are complex and slow , If you put the business logic into the database , It will limit the rapid development of the business . It is suggested to advance the business logic , Put it in the front-end or middle logical layer , And take the database as the storage layer , Realize the separation of logic and storage .

5、 Subqueries are not recommended For subqueries ,mysql The sub query results will be returned to the external table , And scan the external table

6、 It is recommended that the fields be large 、 Fields with low access frequency are split into separate tables to store , Separate hot and cold data

When our table is similar to TEXT Or big VARCHAR Type of large field when , If we don't need this field most of the time we access this table , We should split it into separate tables , To reduce the storage space occupied by common data . One obvious benefit of this is that the number of data pieces that can be stored in each data block can be greatly increased , Both reduce Physics IO frequency , It can also greatly improve the cache hit rate in memory .

7、 Suggest using in() /union Replace or, And pay attention in The number of ( The number depends on the specific situation )

8、 It is recommended not to use mysql stored procedure 、 trigger 、 Functions, etc ( As the case may be )

It's easy to combine business logic with DB Couple together , And for the current data volume stored procedure 、 trigger 、 Functions and so on have no advantage ( stored procedure 、 Functions have great advantages in processing large amounts of data and complex business logic ), and mysql Stored procedures also have certain BUG.