Tag:count

  • MySQL learning notes (5): operators

    Time:2021-4-21

    This article is updated on June 14, 2020, using MySQL 5.7 and operating system deepin 15.4. catalog Arithmetic operator Comparison operator Logical operators Bitwise Operators Operator priority Arithmetic operator operator grammar explain + a + b addition – a – b subtraction * a * b multiplication / a / b Division. similarDIV, butDIVThe results […]

  • The difference and implementation of select count (*), count (1) and count (column)

    Time:2021-4-21

    In SQL server, count (*) or count (1) or count ([column]) is probably the most commonly used aggregate function. In fact, many people can’t distinguish the three. This article will elaborate the function, relationship and the underlying principle of the three. Usually, I often see some so-called optimization suggestions that use count (1) instead of […]

  • State consistency

    Time:2021-4-18

    state In Flink, fault tolerance, state consistency and checkpoint mechanism are realized by state, Generally speaking, the state is to back up the data or the intermediate results of program operation, which can ensure that the program can recover from the midway error; State type What are the specific types of saved states in the […]

  • Interviewer: what is the garbage collection mechanism of PHP

    Time:2021-3-31

    Interview questions: selected topics. PHP interview questions about PHP’s garbage collection mechanism. PHP’s garbage collection mechanism refers to GC mechanism. PHP can automatically manage memory and clear unnecessary objects. PHP interview questions share PHP’s interview questions about garbage collection mechanism My PHP learning and communication community-1023755567. Group management is ready, bat and other advanced knowledge […]

  • Reread Windows core programming – 003 – kernel object

    Time:2021-3-29

    Kernel object is a relatively difficult concept to understand. The root of the problem lies in that even in the book core programming, it does not clearly define it, but constantly illustrates and describes its properties and how to use it. A blind man can’t see the whole picture.We can only enumerate its properties as […]

  • How to enhance the interceptor of grpc

    Time:2021-3-24

    Grpc interceptor as AOP programming tool, I believe you must have experienced when using grpc. Here, we mainly talk about the shortcomings of normal use It can only be used for global, and can’t flexibly intercept each or a class of methods. If you only do some business independent operations (record the request log and […]

  • Python packet processing

    Time:2021-3-19

    In daily data analysis, we often encounter tasks that need to be grouped by column, such as calculating the number of people in each department of a company, calculating the average wages of men and women in each department, calculating the average wages of employees in different years, and so on. In this kind of […]

  • Introduction of iota in golang

    Time:2021-3-14

    iotaIt’s an ancient Greek lettergolangRepresents a constant counter in The rules used are as follows: wheneverconstWhen it appears, it will makeiotaInitialize to 0 constEach new line of constant declaration in theiotaCount once Let’s look at the sample code Const A0 = iota // A0 = 0 // const appears and iota is initialized to 0 […]

  • Incomplete record of object and memory in IOS

    Time:2021-3-14

    Type system Reference type Class Pointer Block Value type Basic data types (int, float, double…) Structure Enum (enum) Type decoration Protocol Category Extension variable Member variable: the variable defined in @ interface {} @Public: public access, even if defined in. M file @Private: private access, default Use self – > valuename to access Property: variable […]

  • Bucket sorting is so easy

    Time:2021-3-8

    [toc] preface Statement: refer to the Internet, you can leave a message if you have any dispute. Only by standing on the shoulders of our predecessors can we see further. This tutorial pure hand play, dedicated to the most practical tutorial, do not need any reward, just hope to forward more support.Welcome to my official […]

  • Redis real combat 08. Realize automatic completion, distributed lock and counting semaphore

    Time:2021-3-8

    Automatic completionP109 Automatic completion can be seen everywhere in daily business, which should be regarded as the most common and common function. The actual business scenario must include the case of containing substrings. In fact, to a certain extent, this is converted into the search function, that is, the string containing a certain substring, and […]

  • Flink learning — a detailed explanation of incremental checkpoint for managing large state

    Time:2021-2-24

    The article is reproduced from:https://ververica.cn/develope…Author: Qiu Congxian (Shan Zhi) Apache Flink is a stateful flow computing framework. The state is the memory state that has been processed in the job operator for subsequent processing. State is very important in many complex scenarios of flow computing Save all the historical records to find some kind of […]