Software test interview questions (4)

1、 The difference between compilation errors and running errors

• Compilation errors generally refer to syntax errors or obvious logic errors , Such as : Semicolon missing , Write fewer parentheses , Key words written wrong etc
• A run error is a logical error that results from running without a compile error , Such as : Null pointer exception , Divisor is 0 , Cross border visits, etc

2、 Stored procedure of database

stored procedure （Stored Procedure） It's on a large scale Database system in , A group of SQL Statements set , It's stored in a database , once compile After the permanent effect , The user specifies the name of the stored procedure and gives the parameters （ If the stored procedure has parameters ） To execute it. . Stored procedure is an important object in database . In the case of a huge amount of data, the use of stored procedures can achieve double speed efficiency .

3、 How to optimize the efficiency of database query

MySQL Common database query performance optimization methods

How to optimize the query efficiency of the database

Choice of storage engine ： If the data table needs to support transaction processing , We should consider Innodb engine , Because it completely conforms to ACID Characteristics of ; If the data table does not need to support transaction processing , Then use the storage engine MyISAM

• Optimize the query , Try to avoid using full table scanning , The first thing to consider is where as well as order by Build the corresponding index on the column involved in the sentence
• Try to avoid where Clause != perhaps > , < Wait for the operator , Otherwise, the storage engine will give up using indexes , And do a full table scan
• Try to avoid where Clause null Value for judgment , Otherwise, the storage engine will give up using indexes , And do a full table scan
• Try to avoid where Clause or The judgment of the , If a field has an index , A field has no index , It will cause the engine to abandon the use of indexes , And do a full table scan
• The following query will also result in a full table scan ：( The leading percent sign cannot be used ) select id from t where name like ‘%abc%’;
• It is clear that not all indexes are valid for queries ,SQL Query optimization is based on the data in the table , When there is a large amount of duplicate data in the index column , Queries may not use indexes , If there are fields in a table sex, When men and women occupy almost half , So even in sex It's indexed on , It also has no effect on query efficiency
• The more indexes, the better , The index can improve the corresponding select The efficiency of , But it also reduces insert and update The efficiency of , because insert and update It's possible to rebuild the index , Cause two queries , So how to build an index needs careful consideration , As the case may be
• Try to use numeric fields , If only contains the numerical value information the field as far as possible does not design for the character type , Set to character type, which will reduce the performance of query and connection , And it increases storage overhead . This is because the engine compares each character in the string one by one when it processes queries and connections , For digital data , Just one comparison is enough
• Should try to avoid in where The clause performs an expression operation on the field , This will cause the engine to abandon indexing , And do a full table scan （ for example ： select id from t where num=100*2; ）
   

4、 Database optimization scheme

How to optimize the query efficiency of the database

• When designing tables , Design tables in strict accordance with database design specifications
• Use the cache , Make frequent visits to , And the data that does not need to change frequently is put in the cache , Can reduce the number of disks IO Number of reads and writes , Because disk IO The transmission speed is very slow
• use mysql Self contained table partitioning technology , Divide the data into different files , It can improve the reading and writing efficiency of the disk
• Choose the right engine , Parameter optimization （ It works char(10), You don't have to char(20)）
• Do not use full-text search
• Avoid frequent creation and deletion of temporary tables , To reduce the consumption of system table resources
   

5、 ... and 、B/S The architecture and C/S Definition and difference of architecture （ Difference ）

One 、B/S The architecture and C/S Definition of Architecture

1、B/S（Browser-Server） Browser and server architecture . ( For example, Baidu. 、 Microblogging 、 Taobao and other websites )

Including the sender browser 、web application server 、 Database server software system . Users only need a browser to access the service . When the system is updated , Just update the server , No need to update browser .

2、C/S（Client-Server） Client and server architecture .( For example, wechat 、 King glory mobile Tour ,QQ Music and other software ).

C/S Structure and B/S The most significant difference is the need to install the client , Access the application system through the client program . So when the system is updated , Update the server , Also update the client .

Two 、B/S And C/S difference （ Difference ）

1、 The hardware environment is different :

C/S Built on a private network , Small scale network environment （ relative B/S）, The LAN provides connection and data exchange services through special servers .

B/S Built on Guangcheng online , No special network hardware environment is needed

2、 Different safety requirements :

C/S Generally for relatively fixed user groups , Strong ability to control information security , General highly confidential information system adopts

B/S Built on Guangcheng online , Weak control over security , User base for unknowable users .

3、 System maintenance is different :

C/S Because of the integrity of the program , It must be examined as a whole , Upgrading is difficult , More based on Windows On , There are limited ways of expression , High requirements for programmers .

B/5 Seamless system upgrade , Maintenance costs are small , There are richer forms of expression , Development is less difficult .

4、 Dealing with problems is different :

C/S Handle user fixed , High security requirements , Require the same operating system .

B/S For all users , Widely dispersed , Small requirements for the system .

6、 ... and 、 What are automatic boxing and automatic unpacking

java For every basic type, the corresponding packaging type is provided in .

byte,short,char,int,long,float,double and boolean

Byte,Short,Character,Integer,Long,Float,Double,Boolean.

Automatic packing is Java Automatically convert the original type value to the corresponding object , For example, will int The variables of are converted to Integer object , This process is called packing , And vice versa Integer Object conversion to int Type values , This process is called unpacking . Because the packing and unpacking are automatic non-human conversion , So it's called automatic packing and unpacking .