Tag:Equivalence

  • Analysis of five join strategies of spark

    Time:2021-1-26

    Join operation is a very common data processing operation. As a unified big data processing engine, spark provides very rich join scenarios. This article will introduce five join strategies provided by spark, hoping to help you. This paper mainly includes the following contents Factors affecting join operation Five strategies of join execution in spark How […]

  • Regular expressions commonly used in JS

    Time:2021-1-24

    A common regularization method   1   \  :Marks the next character as a special character, an original character, a backward reference, or an octal escape character. For example, “d” matches a numeric character, not the letter D.   2  ^  : matches the start position of the input. If the multiline flag is set to true, […]

  • cmder tips(qbit)

    Time:2021-1-14

    Releases:https://github.com/cmderdev/cmder/releases/ Right click a directory to open the cmder cdmer /register user or cmder /register all If the cmder prompts that api-ms-win-crt-runtime-l1-1-0.dll is missing, installVc2015 runtimeThat’s it. Chinese characters overlap: Settings > main, cancel “monospace”. Add alias: edit the config / aliases file. For example: ll=ls -alF –show-control-chars 1.3. X: Settings > startup > environment. set LANG=zh_CN.UTF-8 CHCP UTF-8 # is […]

  • Regular expression metacharacter

    Time:2021-1-12

    Common metacharacter table Match character Metacharacter explain \ Marks the next character as a special character, or a literal character, or a backward reference, or an octal escape character. For example, ‘n’ matches the character ‘n’. ‘\ n’ matches a newline character. The sequence ‘\ \’ matches’ \ ‘and’ \ (‘matches’ (‘ \cx Matches the […]

  • Python text processing and regular expressions

    Time:2020-12-20

    [unfinished draft]This week, I encountered a lot of work that needed to add, delete, check and modify a character. For the first time, I used my own script to do it. As a result, the reusability was not high, and the efficiency was not very good. I also used the regular expression part re in […]

  • MySQL learning notes: index failure

    Time:2020-12-17

    Series articles: MySQL learning notes: combination index – leftmost principle MySQL learning notes: Composite Index – index push down MySQL learning notes: index failure When type in explain is range and rows is too large: For the meaning of rows and the enumeration value of type, please refer to:EXPLAIN Output Format Query threshold example: General […]

  • How to find the intersection, union, difference and symmetric difference set of the set in Python.

    Time:2020-11-23

    In fact, intersection, union, difference and symmetric difference sets are also special operations of sets. A & B: the common element of two sets of intersection table, equivalent to A. intersection (b) A | B: Union table all elements of two sets, equivalent to A. Union (b) A-B: elements of difference table belonging to a […]

  • Unveiling tidb new optimizer: analysis of cascade planner principle

    Time:2020-11-20

    Author: Mingcong Han In “ten minutes as a contributor series | adding optimization rules for cascades planner”, we briefly introduced the background knowledge of cascades. This paper will introduce the framework and principle of cascades planner, a new optimizer of tidb. Brief introduction of tidb current optimizer The function of query optimizer in relational database […]

  • Front end training – intermediate stage (36) – Vue 2. X component definition and use, communication between components

    Time:2020-11-20

    The most basic part of the front end isHTML+CSS+Javascript。 If you master these three technologies, they are just beginners. Now the definition of front-end development is far more than these. Front end small class(HTML/CSS/JS)In line with the central idea of improving the level of technology and laying a solid foundation of knowledge, we have started […]

  • Equivalent connection and natural connection

    Time:2020-11-17

    1. First of all Tuples: rows in relationships Properties: columns in relationships Relation operation: R (a, B, C, d) and S (B, C, y, z) are two relations; Select [get qualified tuples in relation R] Projection [get some attribute columns in relation R to form a new relation] Join [Select tuples satisfying conditions among attributes […]

  • Regular expressions (notes)

    Time:2020-11-14

    Online regular testing tool:http://www.regexpal.com/ grammar Regexp: regular expression describes a pattern of string matching that can be used toCheck whether a string contains a seed string、Replace the matching substringperhapsTake a substring that meets a certain condition from a stringEtc. Common characters Normal characters include all printable and nonprintable characters that are not explicitly specified as […]

  • Explain through a slow SQL optimization

    Time:2020-10-10

    preface Some time ago, I took over an API call statistics project for internal use of the company. Recently, I received a frequent alarm about slow SQL. I happened to be learning this content recently. Let’s practice. Practical operation This slow SQL mainly involves two tables. API_ Result — used to count API call results […]