Safety foundation 2

Homework 1： In strict mode , Lead to MySQL5.7 Failed to create a new user by inserting the user table , How to modify strict mode

Strict mode introduction ：

Strict mode control MySQL How to deal with illegal or missing input values SQL.

5.6 Of mode yes NO_ENGINE_SUBSTITUTION, In fact, it means a null value , It's equivalent to no mode settings , It can be understood as a relaxed model . If the setting is loose mode , So when we insert data , Even if it's given the wrong data , It may also be accepted , And don't report mistakes . 

5.7 Of mode yes STRICT_TRANS_TABLES, That's the strict model . Developing 、 test 、 In production and other environments, most of them adopt strict mode . 

Inquire about MySQL The pattern of ：select  @@sql_mode;

sql_model Introduction of value ：

1. NO_ZERO_IN_DATE： This pattern affects whether the month and day in the date are allowed to include 0. If this mode is enabled ,2016-01-00 It's not allowed , however 0000-02-01 Permissible
2. NO_ZERO_DATE： Set the value ,mysql Database is not allowed to insert zero date
3. ONLY_FULL_GROUP_BY： Appear in the SELECT sentence 、HAVING Conditions and ORDER BY Column in statement , Must be GROUP BY The columns may depend on GROUP BY Function columns of columns .
4. NO_AUTO_VALUE_ON_ZERO： This value affects the insertion of self growing columns . By default , Insert 0 or NULL Represents the generation of the next self increasing value . If the user wants to insert a value of 0, And the column is self-growing , So this option works .
5. STRICT_TRANS_TABLES： In this mode , If a value cannot be inserted into a transaction table , Then interrupt the current operation , No restrictions on non transaction tables .
6. ERROR_FOR_DIVISION_BY_ZERO： stay INSERT or UPDATE In the process , If the data is divided by zero , It's a mistake, not a warning . If the mode is not given , So when the data is divided by zero ,MySQL return NULL.
7. NO_AUTO_CREATE_USER： prohibit GRANT Create a user with a blank password .
8. NO_ENGINE_SUBSTITUTION： If the required storage engine is disabled or not compiled , Then throw an error . When this value is not set , Replace... With the default storage engine , And throw an exception .
9. PIPES_AS_CONCAT： take ”||” Treat as the concatenation operator of a string, not as the or operator , This sum Oracle The database is the same , And string concatenation function Concat Similar .
10. ANSI_QUOTES： Enable ANSI_QUOTES after , You can't use double quotes to refer to strings , Because it's interpreted as an identifier .

How to modify strict mode ：

1. Temporary session modification , Invalid closing session ：set sql_mode = ' Modified value '    or     set session sql_mode=' Modified value ';

2. The current service is modified , Starting the service again is invalid ：set global sql_mode = ' Modified value ';

3. Permanent modification ： stay my.cnf Add ：

[mysqld] sql_mode=ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER

And then restart mysql take effect .

Homework 2： Try to all Change it to select jurisdiction , And will * . * Change to specified database

Homework 3:16kb page Or other parameters at present , Is it possible to modify ？

B+ The characteristics of the tree ：

1. No data is stored on non leaf nodes , Store only key values , and B The tree node not only stores the key value , It also stores data .
2. innodb Middle page The default size is 16KB, If you don't store data , Then more key values will be stored , The order of the corresponding tree ( The child tree of a node ) It will be more Big , The trees will be shorter and fatter , So we look up the data for disk IO The number of times will decrease again , The efficiency of data query will be faster .
3. B+ All data in the tree index is stored in the leaf node , And the data is in order , Linked to the list . that B+ Trees make range lookups , Sort search , Group search and de duplication search become very simple .
4. B+ The tree is made of N It exists in the form of a fork tree , This effectively reduces the height of the tree , You don't need a full table scan to find data , Looking down the root node layer by layer can Quickly find our target data ,

B+ The parameters of the tree can be modified .

• Page default 16KB
• File Header、Page Header Wait for a total of 102 Bytes
• Infimum + Supremum Accounting for 13 Bytes
• Record head 5 Bytes
• id Zhanwei int, Occupy 4 Bytes
• The offset of page directory accounts for 4 Bytes

1.     Index records that non leaf nodes can store =  ( Page size - File Header - Page Header - ...) / ( Recording head + Primary key + Page offset ）​​​​​​​
2. Data records that leaf nodes can store =  ( Page size - File Header - Page Header - ...) / ( Primary key + Field + The offset of the next record )

Homework 4: understand MySQL Triggers and stored procedures for ?

　1、 trigger ： On the designated table ,(insert( Insert )、update( modify )、delete( Delete )) Event action , Trigger （After( after ) opportunity ,Before( Before )）, Execute a designated group or group sql sentence . Simply put When we execute a sql At the time of statement , This article sql The execution of the statement will automatically trigger the execution of other sql sentence .

The four elements created by the trigger ：

1. Surveillance location （table）
2. Monitoring events （insert/update/delete）
3. Trigger time （before/after）
4. Triggering event （insert/update/delete）

   2、 stored procedure （Stored Procedure） It's a complex program stored in a database , A database object that can be called by an external program . Stored procedures are designed to accomplish specific functions SQL Statements set , Compiled, created and stored in a database , The user can specify the name of the stored procedure and give the parameters ( When needed ) To call execution . Stored procedures are very simple in mind , Database SQL Language level code encapsulation and reuse .

advantage :       

1. The operation is relatively stable .
2.   Reduce the interaction between business system and database , To reduce the coupling , Database interaction is faster .

shortcoming :

1. MySQL Stored procedure and Oracle Is weaker than , The demand of the Internet industry changes rapidly, so it is less used .
2. The migration of stored procedures is very difficult , Database cluster environment , It is also very difficult to ensure the consistency of stored procedure changes between Libraries .
3. The maintenance process is also very troublesome .

Homework 5: substr Functions and substring Difference of function ?

SQL in substr The usage function ：substr() Function returns part of a string .

• grammar : substr(string,start,length)
• string： The specified string to intercept .
• start： It's necessary , Specify where to start the string .
• Positive numbers ： Start at the specified position of the string
• negative ： Starting at the specified position at the end of the string
• 0： Start at the first character in a string
• length ： Specify the length to intercept .

SQL in substring The usage function ： Return character 、 Binary system 、 Part of the syntax of a text or image expression : substring ( expression, start, length )

difference ：

1. substring(start,stop)   ：  The two parameters are the start and end positions , Include “ rise ”, barring “ stop ”, In terms of intervals, that is [start,stop)
2. substr(start,length)：  The first parameter is the starting position , The second parameter is to intercept the length of the string

Homework 6: truncate and delete The difference between ? 

1. delete You can follow where Conditions ;truncate No terms
2. delete After deletion, the number of affected lines is displayed ;truncate No affected rows are displayed
3.  delete It is data deletion one by one , Low efficiency ;truncate Is to delete the entire table , Creating an identical table structure , Efficient
4.  delete After deletion, the auto increment is based on the original maximum ;truncate Will start over
5. deleter Except that it can be rolled back ;truncate Cannot be rolled back
6. delete Deletion is slower than truncate