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introduction Regular expressions are special strings used to match text (character set). If you want to extract a phone number from a text file, you can use a regular expression. If you need to find all files with numbers in the middle of the name, you can use a regular expression. If you want to find all duplicate words in a text block, ...

Query analysis and tuning backgroundIn the process of using the database, we often encounter the sudden slow down of SQL due to the following problems:Select wrong indexSelect the wrong connection orderRange queries use different quick optimization strategiesExecution method change of sub query selectionChange of policy mode of semi connection ...

Since this article is a summary written after the completion of the system, many operation results show the final results after the completion of the system, which will be different from the corresponding SQL execution results. 1, Introduction requirement: Complete a simple application system design and development. Background: In th ...

Chapter 57 SQL command INTO A SELECT clause that specifies that the selected value is stored in the host variable. outline INTO :hostvar1 [,:hostvar2]... parameter : hostvar1 - the output host variable declared in the host language. When specified in the INTO clause, the variable name is preceded by a colon (:). Host variables ...

2021SC@SDUSC hbase source code analysis (V) HLog analysis 2021SC@SDUSC2021SC@SDUSC 2021SC@SDUSC2021SC@SDUSC 2021SC@SDUSC2021SC@SDUSC HLog By default, the data of all write operations (write, update and delete) are written to the HLog in the form of append first, and then to the MemStore. In most cases, the HLog will not be read, but if ...

catalogue preface 1, Index and classification 1. Concept of index 2. Function of index 3. Side effects of index 4. Classification of index 4.1 General Index 4.2 unique index 4.3 primary key index 4.4 full text index 4.5 combined index (single column index and multi column index) 5. Principles and basis of index creation 2, Create ...

When the client connects to the MySQL server, it must provide valid identity authentication, such as user name and password. When the user performs any database operation, the server will verify whether the user has corresponding permissions. For example, SELECT permission is required for query tables and DROP permission is required for deletin ...

introduction Database transaction refers to a series of operations performed as a single logical unit of work, either complete or not at all. Under normal circumstances, these operations will proceed smoothly and finally succeed. However, if there is a problem in any link in this series of processes, all information in the database must ...

catalogue Database modeling and database and table building mysql database programming connection and data insertion   On Node   Insert information on the database Server through SQL statements on the Server Query operation of mysql database mysql data deletion and stored procedure call Full code: Database modeling and data ...

Open MongoDB service with configuration file: ./mongod -f /mongodb/single/mongod.conf /mongodb/single/mongod.conf is where the configuration file is located Open MongoDB mongo --host=192.168.56.101 192.168.56.101: the ip address of the remote MongoDB server is not written – port means the default port is used for login Databases man ...