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Subquery Subqueries refer to SELECT clauses that appear in other SQL statements. For example: SELECT * FROM t1 WHERE col1 = (SELECT col2 FROM t2); Among them, SELECT * FROM t1 is called Outer Query/ Outer Statement (that is, the outer query) SELECT col2 FROM t2, called SubQuery Subqueries are nested w ...

Java emoji persistence mysqlI haven't updated my blog for a long time. Today I share with you a question about emoji expression persistence. I believe that web developers have encountered such a problem, because we know that MySQL utf-8 character set can't save emoji expression characters. Why? Because ordinary strings or expressions occupy 3 b ...

Originality: Yang Taotao MySQL has always supported regular matching, but regular substitution was not supported until MySQL 8.0. For such scenarios, it used to be either processed on MySQL or processed on Application side. For example, I want to replace the substring of the third action in the column str1 of table y1 with dble. 1. Write you ...

Preface Anyone who can read this article must know the power and benefits of the separation of reading and writing from the database, so let's cut the crap and get right to the point. For convenience, you can configure database remote connection privileges first use mysql ; update user set host = '% ...

If you want to modify the storage engine of MySQL database, you must understand the two engines, and clearly understand the difference between the two engines. MySQL database supports two common storage engines: InnoDB engine: Provides support for database ACID transactions, and implements four isolation levels of the SQL standard. The engine ...

affair Transaction actually refers to a set of operations that contain many single logic. As long as one logic fails to execute successfully, it fails. All data is returned to its original state (rollback) Why do we have business? To ensure the success of logic. Example: Bank transfer. Demonstrate transactions using the command line. Op ...

Articles Catalogue 1. Common Column parameters 2. query query function use 3. Common filter conditions of filter method 4. SQLALchemy Implementing Foreign Key and Its Four Constraints 5. ORM-level foreign keys and one-to-many relationships 6. ORM-level foreign key and one-to-one relationship implemen ...

The basic introduction and basic usage of nmap have been submitted in the dark cloud knowledge base, and the details are more detailed, which will not be described in this article. Specific links: /tips/?id=2002 This article mainly explains the use of many scripts of nmap, especially when penetrating the intranet. 0x01 nmap Scanning by Script ...

Originator: Yang Taotao   Before MySQL 8.0, let's assume there was a bad SQL. mysql select * from t1 order by rand() ; Running with multiple threads, causing the CPU to run full and other requests to be blocked.What about this?(   There are probably several solutions: Set max_execution_time to prevent reading SQL for too long.The poss ...

I. Environmental Construction 1. Install Elastic Search Installing Elastic Search-7.2.0 in MacOS is a very simple procedure, which can be accomplished with a few lines of commands. Here are the installation steps # Download the Elastic Search program wget https://artifacts.elastic.co/downloads/elasticsearch/elasticsearch-7.2.0-darwin-x86_64.tar ...