disadvantages of caffeine

; try {//Load Database driver Class.forName ("Com.mysql.jdbc.Driver"); Get the database link through the data-driven management class connection =drivermanager.getconnection ("Jdbc:mysql://localhost:3306/mybatisdata?characteren Coding=utf-8 "," root "," root "); Define SQL statements, where? Identity placeholder String sql = "SELECT * from user where id =?"; Get preprocessing statement preparedstatement = connection.preparestatement (sql); S

that the composite column length cannot be too long; In a composite index, all columns must be from the same table, and composite columns cannot be created across tables In a composite index, the order of the columns is very important, so the order of the columns is carefully arranged, in principle, the most unique column should be defined first, for example, the index on (col1,col2) is not the same as the index on (col2,col1), because the order of the two-indexed columns is different ; for the

composite index, the total length of the columns that make up the composite index cannot exceed 900 bytes, which means that the composite column length cannot be too long; In a composite index, all columns must be from the same table, and composite columns cannot be created across tables In a composite index, the order of the columns is very important, so the order of the columns is carefully arranged, in principle, the most unique column should be defined first, for example, the index on (col1

Summary of advantages and disadvantages of ORACLE five tables:1, Normal table (heap table): Suitable for most design scenarios, there are advantages and disadvantages.Advantages:A, the syntax is simple and convenientb, suitable for most scenesDisadvantages:A, the update log cost is largeB,delete Cannot free space (HWM high water mark does not drop)C, table record too large retrieval too slowD, index back table read overheadE, even if inserted in order

the gender column of the personnel table, in the results of the query, the data rows of the result set occupy a large proportion of the data rows in the table, that is, the data rows that need to be searched in the table are large. Increasing the index does not significantly speed up the retrieval. Third, for those columns defined as text, the image and bit data types should not be indexed. This is because the amount of data in these columns is either quite large or has very little value. The i

the form of a two-dimensional table! a two-dimensional table is made up of rows and columns, knowing that the row and column numbers will be able to locate the data in the table! Excel is a two-dimensional table! Easy to use, the basic common SQL language makes it easy to operate relational databases! SQL is supported , so complex queries can be made! easy to maintain, rich integrity (domain integrity, entity integrity, referential integrity, and custom integrity) greatly reduces data redun

exceed 900 bytes, which means that the composite column length cannot be too long; In a composite index, all columns must be from the same table, and composite columns cannot be created across tables In a composite index, the order of the columns is important, so the order of the columns is carefully arranged, in principle, the most unique column should be defined first, for example, the index on (col1,col2) is not the same as the index on (col2,col1), because the order of the two-indexed colum

This article focuses on the details of Ajax, the origin of Ajax, the principle of Ajax, and the advantages and disadvantages of Ajax. Now let's see this article together. What is Ajax In fact, Ajax already belongs to the old technology, and now almost no one will use, here is mainly the bottom of the things to share with you, in case of loading the interviewer. Ajax, "Asynchronous JavaScript and XML" (Asynchronous JavaScript and XML), refers to a web

created, it waits for the first time to execute. At that time, the stored procedure was optimized, and the query plan was compiled and cached on the system. When you run the stored procedure several times, the cached query plan is used instead of creating a new query plan, unless specified by using the WITH RECOMPILE option. This means that each time the stored procedure is used, the stored procedure skips a lot of optimizations and compilation work. The exact time to save depends on the comple

version determines the stability of the RAC operation. It is important for database engineers and hardware engineers to have extensive environmental checks, validations, and extensive testing after deployment before installing the configuration.　　Second, high-performanceHigh performance is also a major headache for migrating from a single machine environment to a RAC environment, and RAC is not a high-performance solution. In the current hardware environment of gigabit Network, many times the s

complexity of the application index-ready file is O (n).C) Poll use Nfds to specify the maximum number of file descriptors and events to listen to, this number can reach the system agreed to open the largest file description of the descriptor. That is, 65535.D) can only work in the LT mode.3) Epoll:A) epoll the file Description descriptor and events of the user's booklet into the event table in the kernel. Provides a stand-alone system call Epoll_ctl to manage user events, and epoll the way cal

Label:The benefits of a relational database:1. Maintain data consistency (transaction processing)2. Due to standardization, the cost of updating data is small (the same fields are basically only one place)3. Complex queries such as joins can be madeOne of the best advantages of relational databases is the ability to maintain data consistency.The lack of a relational database:Not good at handling1. Write processing of large amounts of data2. Index or table structure (schema) changes for tables wi

Summary of advantages and disadvantages of machine learning common algorithmsk Nearest Neighbor : The algorithm uses the method of measuring the distance between different eigenvalues to classify.Advantages:1. Easy to use, easy to understand, high precision, mature theory, can be used to do classification can also be used to do regression;2. Can be used for numerical data and discrete data;3. The training time complexity is O (n); no data input assump

With the proliferation of Unified Communication Technology, many enterprises are actively involved in deploying a unified communication system. However, many enterprises do not know much about this. This article will summarize the advantages and disadvantages of deploying Unified Communication for an example, and provide you with reference materials, hoping to help you understand this aspect. For CIOs, the process of deploying a Unified Communication

Why are more and more php veterans recommending yii, cakephp, ci and other frameworks instead of domestically-developed well-known thinkphp frameworks? Is thinkphp having any disadvantages that other frameworks do not have? Why are more and more php veterans recommending yii, cakephp, ci and other frameworks instead of domestically-developed well-known thinkphp frameworks? Is thinkphp having any disadvantages