Tag:Indexes

  • SQL Server million level database optimization scheme

    Time:2020-5-13

    1. In order to optimize the query, we should try to avoid full table scanning. First, we should consider building indexes on the columns involved in where and order by. 2. Try to avoid null value judgment on the field in the where clause, otherwise the engine will give up using the index and scan […]

  • Magic MySQL performance analysis artifact of SQL → explain, the cornerstone of SQL takeoff!

    Time:2020-5-11

    Preface a moment of fun Someone raises a pig and wants to let it go. But the pig knows the way home and comes back several times. One day, the man thought of a tough way. He drove the pig around the mountain and let it go. After releasing the pig, he went around again. […]

  • Technology sharing | InnoDB handler | read * variable interpretation

    Time:2020-5-10

    Author: Gao PengAt the end of the article, there is his book “in-depth understanding of MySQL master-slave principle 32”, in-depth understanding of MySQL master-slave, gtid related technical knowledge.Source version: percona 5.7.14This is a learning record. Please understand if there is any mistake. In this paper, it is recommended to watch on the PC side, with […]

  • Web database management platform KB DMS: function introduction [1]

    Time:2020-5-10

    Brief introduction of Web database management platform Recommend a self-developed open source web database management tool:kb-dms Open source project address: KB DMS, if you can help, please point a star. Thank you~ This tool has the following features: Authority control:Avoid the risk of uncontrollable data source permissions, and avoid data and database tables being modified […]

  • How to build adaptive hash index

    Time:2020-5-9

    Reproduced from official account: Graphic MySQL Adaptive hash index (hereinafter referred to as AHI) is estimated to be one of the major features of MySQL. Everyone knows its name, but it is the most ambiguous feature. In this issue, we will explain how AHI is built. First, let’s think about what AHI is to solve: […]

  • Interviewer: how to optimize SQL?

    Time:2020-5-8

    During the interview, the interviewer asked: how do you design your table structure and draw an E-R chart? Then continue to dig deep, if there is slow query, how do you optimize your SQL? Today, I will talk about how to answer this question. First of all, we should not panic. We are doing the […]

  • [teacher Zhao Qiang] delete table and Oracle recycle bin

    Time:2020-5-8

    1、 DROP TABLE statement of Oracle First, let’s look at the syntax format of Oracle drop table. Explain the parameters: schema Schema represents the scheme name, which can be understood as user name. It defaults to the table under the current user. For example, to delete the EMP table under Scott user, drop table scott.emp […]

  • JQuery operation select drop-down box

    Time:2020-5-8

    Get text and value selected by select $(“ා” select “Id”). Change (function() {/ / code…}); / / add an event for select and trigger when one of the items is selected Varchecktext = $(“” select “Id”). Find (“option: selected”). Text(); / / get the selected text Varcheckvalue = $(“” select “Id”). Val(); / / get […]

  • Realization principle of skip meter

    Time:2020-5-8

    Realization principle of skip meter It is a dynamic data structure, which can support fast insert, search and query operations. It is not complicated to write, and can even replace red black tree For a single linked list, even if the data stored in the linked list is in order. If we want to find […]

  • Leetcode 3. Longest substring without repeating characters

    Time:2020-5-8

    thinking Use aidxIndicates the start position of the current substring class Solution: def lengthOfLongestSubstring(self, s: str) -> int: m = dict() ”’ For each char c, if continue does not appear There are: Before the index of the current string: continue After: one bit after the map position ”’ idx = 0 res = 0 […]

  • Linux and windows disk file types

    Time:2020-5-7

    Linux and windows disk file types Windows file type classification There are three main types: FAT Fat, file allocation table is used by the operating system to track the location, size and other information of various files stored on the disk. Doc (disk operation system) is a typical representative of fat file system. Fat file […]

  • Oracle basic syntax

    Time:2020-5-7

    Oracle supports five types of integrity constraintsNot null (non null) – prevent null value from entering the specified column. It is defined on a single column basis. By default, Oracle allows null value in any columnCheck – checks that the conditions specified in the constraint are metUnique – ensure that there are no duplicate values […]