Tag:count

  • On lemda’s expression

    Time:2021-7-1

    General query db.User.Select(u => u); // Query without condition db.User.Where(u => true); // Query without condition db.User.Where(u => u.username == “wjl” || u.username == “hyf”); // Conditional query ||| means “or” & & means “and” DB. User. Select (U = > U. username. Endswith (“Li”))// Fuzzy query is equivalent to like ‘%’ DB. User. Select […]

  • Reading notes of objc runtime source code (1)

    Time:2021-6-18

    Reading notes of objc runtime source code (1) My blogMax’s BlogThe source code of this article comes fromapple opensource。 1.objc-private.h Open the header file to see two familiar structure pointers typedef struct objc_class *Class; typedef struct objc_object *id; We use it a lotidThis pointer is olderFoundationFramework, the general initialization method will return aidObject, and some […]

  • The concurrent call and use example of spool coroutine

    Time:2021-6-17

    Example 1: Using the feature that the channel pop will automatically suspend the current coroutine and wait for the producer to push the data, the concurrent call is realized, and the result set is combined after the coroutine is completed. $serv = new Swoole\Http\Server(“127.0.0.1”, 9503, SWOOLE_BASE); $serv->on(‘request’, function ($req, $resp) { $chan = new Swoole\Coroutine\Channel(2); […]

  • The difference and execution of select count (*) and count (1) in SQL Server

    Time:2021-5-10

    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 […]

  • Garbage collection mechanism of PHP

    Time:2021-5-6

    Interview 10 companies, get 9 offers, PHP interview questions in 2020 PS: This article includes selected interview questions and knowledge. 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 […]

  • JavaScript — operator, process control

    Time:2021-5-5

    1、 Operator 1. Arithmetic operator Arithmetic operator + – * / % ++ — Comparison operator > >= < <= != == === !== be careful: ————————————————- In the assignment operation: I + + means to first give the value of I to the left variable, and then add I on this basis++ ++I stands […]

  • Detailed explanation of php7 garbage collection mechanism

    Time:2021-5-3

    This article is wrong and has no reference value This article is wrong and has no reference value This article is wrong and has no reference value This article is wrong and has no reference value This article is wrong and has no reference value I was interested in this topic a few days ago, […]

  • 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 […]