In C++, Inheritance is one of the core ideas of object-oriented programming. It builds a hierarchical relationship between classes, with the concepts of parent classes and subclasses. This article will summarize the relevant content of base class pointers, derived class pointers and virtual functions, and attach corresponding sample codes. 1. Base class pointer, derived class […]
Tag: derived
SQL optimization – change the derived table into a subquery, the query speed will become faster
Using database: MYSQL 5.7.27 References: Database~Some points to note about Mysql derived tables~About the slow query problem of millions of data https://blog.csdn.net/weixin_34146410/article/details/93984487 Subquery: When a query is nested within another query, the other query becomes a subquery, also called an inner query. Derived tables: When using a subquery in the FROM clause, the result set […]
Derived class and base class pointer pointing
https://juejin.im/post/6844904054930292749 The relationship between a derived class and a base class is not two independent types. In the derived relationship, Derived classis abase class type. In C++ syntax, it is stipulated that a base class pointer can point to a derived class object, But derived class pointers cannot point to base class objects. Use the […]
In-depth analysis of the member construction order and constructor calling order of C++ ordinary classes, derived classes, and virtual base classes
C++ stipulates the syntax rule that “The destruction process of an object must be the opposite of its construction process“. Therefore, after we have thoroughly studied the construction process, the destruction process is naturally the opposite; (Because the initialization and destruction of members of a class is similar to a process of pushing and popping […]
A MySQL bug description and avoidance about derived tables
* Original content from the GreatSQL community may not be used without authorization. Please contact the editor and indicate the source for reprinting. Related articles: MySQL’s optimization and usage restrictions on derived tables 1. Bug description A colleague encountered an interesting statement, saying that the result of a SQL run in MySQL version 8.0.25 is […]
MySQL’s optimized processing and usage restrictions on derived table
* The original content of the GreatSQL community is not allowed to be used without authorization, please contact the editor and indicate the source for reprinting. Foreword With the development of the MySQL version, the optimizer is becoming more and more intelligent, and there are more and more optimizer switches. This article will share with […]
C++ Derived Class Text Query Program Revisited
Query_base class and Query class //This is an abstract base class from which specific query types are derived, and all members are private class Query_base {<!– –> friend class Query; protected: using line_no = TextQuery::line_no;//for level function virtual ~Query_base() = default; private: //eval returns the QueryResult that matches the current Query virtual QueryResult eval(const TextQuery […]
Calculating Derived Metrics in ClickHouse
The core task of indicators is to convert raw data into expert data. Indicators are composed of elements such as dimensions and measures. Sometimes, in order to improve calculation efficiency, derivative measures are defined based on indicator measures at the same time, and multiple values are calculated at one time. If there is the sales […]
The range and content-range parameters of the http header derived from the resumable download
Background Recently, my colleague was doing a breakpoint resume download for Android, and then encountered when adding the RANGE parameter setting in the request header: .addHeader(“RANGE”, “bytes=” + downloadLength + “-” + (contentLength-1)) The information found on the Internet is to set the contentLength. After testing at the same time, it is found that the […]
base class, derived class, polymorphism
Table of Contents base class, derived class, polymorphism 1. Concept leading 1. Inheritance and derivation, one process, two angles 2. The purpose of the derived class 3. If you do not use derived classes, you will encounter problems 2. Derived class specification, derived class and base class relationship 1. Derived class specification 2. Derived class […]