Programmer Think

1. Configure QQ mailbox to send mail 1.1 enable the SMTP service and obtain the authorization code 1.2 select account Start related services and generate authorization code 2. Enable sendmail service and postfile service [root@zydatahadoop001 rundeck]# service sendmail stop [root@zydatahadoop001 rundeck]# chkconfig sendmail off [r ...

SQL HINT (SQL HINT) is an important means to optimize the database, which is to add some hints in sql to optimize the effect. Let's learn about use index, ignore index, and force index; 1. Add use index after the query statement. You can suggest indexes to MySQL for reference, so that MySQL does not consider other indexes. explain select co ...

Recently, someone asked this question in the interview. Before that, they had not studied the specific use logic of the joint index, consulted several articles, and came to some conclusions after testing Test environment: SQL Server 2008 R2 The test results are similar to the query mechanism of MySql joint index. We can think that MySql is the ...

Getting to know JDBC 1, JDBC concept jdbc English full name: java database connectivity is a set of specifications for Java to access database, which can be understood as a set of classes and interfaces provided by java to connect database The relationship between jdbc and database driver: 　　 2, jdbc easy to use Usage process: (the driver jar ...

There are many attributes of fields in MySQL, and the impact on performance can be large or small, so it's necessary to explore the attributes. 1, NULL / NOT NULL For external programs, NULL is an unknown, imprecise, and indescribable value. Therefore, it is clearly stipulated in the development specifications of many companies that it must be ...

According to an example of a project, this paper records and shares the process and relevant settings of python's displaying the content of database to the program interface, and explores the usage of python's operating database. Main contents to be shared: 1. Displays the database contents. 2. Modify database content. 3. The table control spec ...

hibernate -- HQL query summary HQL overview: Simple query of HQL Alias query for HQL: HQL polymorphic query: Sort query for HQL: Paging query for HQL: HQL retrieves a single object: Condition query of HQL: HQL uses aggregate functions: HQL group statistics: Projection query of HQL: HQL ...

Java explains the basic implementation of RPC RPC remote procedure call can be said to be the basis of distributed system. In this paper, we will demonstrate what happens to a normal RPC call through Java. I have seen people ask on the Internet why RPC is called remote procedure call instead of RMC remote method call. In my opinion, RPC is a re ...

1. Functions 1.1 case conversion function function describe LOWER() All lowercase UPPER() uppercase INITCAP() title case 1.2 String Operating Functions function describe concat() Split String Substr (field, startIndex,endIndex) substr length() String Length Instr (field,'character') Location index where specified characte ...

Detailed design of scheduled tasks Timing task is implemented by QuartZ, and QuartZ document reference https://www.w3cschool.cn/quartz_doc/ QuartZ configuration Create a new QuartZ data table in the database. The corresponding SQL table is in the QuartZ.sql file in the current directory Add the quartz.properties file, which provides the relate ...