Category:Database

  • Inner join on will filter out the conditions of null values on both sides

    Time:2020-1-22

    During the work of the previous two days, I met a problem. As for the join on query, I have always been confused about the results. Here is a record. 1. First, look at the following SQL query statement: The result is 25053 2. Add a condition of o.lat = n.lat: The result is 15586 […]

  • Redis statistics UV

    Time:2020-1-22

    How do you do when PM comes up with a demand for statistics page UV / PV? scene There are three options: Leave it to the big data Department of the company and let them get it Start recording the IP address, and then de count the B number / MySQL / redis / HashMap, […]

  • Leetcode data query notes (medium)

    Time:2020-1-22

    626. Change seats Xiaomei is an information technology teacher in a middle school. She has oneseatSeat table, usually used to store students’ names and seat IDS corresponding to them. In whichidIs continuously increasing Xiaomei wants to change the seats of the two students next door. Can you help her write a SQL query to output […]

  • Shardingsphere x Seata, a more consistent distributed database middleware

    Time:2020-1-22

    Recently, shardingsphere, a distributed database middleware, has integrated the distributed transaction capabilities of Seata to create a more consistent distributed database middleware. background In the field of database, the implementation of distributed transaction mainly includes two phases: Xa and base flexible transaction. Xa transaction bottom layer depends on the support of specific database vendors for […]

  • The evolution of high concurrency distributed architecture on the server side

    Time:2020-1-22

    1. overview Taking Taobao as an example, this paper introduces the evolution process of the server architecture from 100 concurrency to 10 million concurrency. At the same time, it lists the related technologies that will be encountered in each evolution stage, so that you can have an overall understanding of the evolution of the architecture. […]

  • Wrong foreach data type used by mybatis results in an error

    Time:2020-1-22

    cause The following error is reported when using mybatis dynamic SQL to traverse conditions: Caused by: java.lang.IllegalStateException: Type handler was null on parameter mapping for property ‘__frch_item_0’. It was either not specified and/or could not be found for the javaType (com.test.Report) : jdbcType (null) combination. at org.apache.ibatis.mapping.ParameterMapping$Builder.validate (ParameterMapping.java:117) at org.apache.ibatis.mapping.ParameterMapping$Builder.build (ParameterMapping.java:104) at org.apache.ibatis.builder.SqlSourceBuilder$ParameterMappingTokenHandler.buildParameterMapping (SqlSourceBuilder.java:123) at […]

  • Insight into the database frontier, gathering the best lineup of Alibaba cloud database, DTCC 2019, top eight highlights

    Time:2020-1-22

    Abstract:As an old friend of DTCC and the world’s leading cloud computing manufacturer, Alibaba cloud database team is invited to participate in this technology event. It will not only send a team of distinguished guests, but also present 8 wonderful topics for the vast number of database industry professionals and users. The following editor combed […]

  • Support “go to o” database evaluation through self-developed database portrait tool

    Time:2020-1-21

    “Go to o” is a hot topic in recent years, which also brings about various doubts, including existing database evaluation, technology selection, etc. Going to o is a systematic project, which needs to be fully evaluated. In this paper, through self-developed tools, generate database portraits, provide first-hand data for o-assessment, and hope to give you […]

  • The difference of two-step permission check in MySQL execution

    Time:2020-1-21

    Original link: he Xiaodong blog The article comes from a question of lemonVersion 8.0 of the document reference in the article Screenshot of the problem: The main test scenario is: the K field does not exist, and there is no select permission. See which error is thrown first, and the result is that the error […]

  • Oracle EBS restart concurrency Manager

    Time:2020-1-21

    Oracle EBS restart concurrency Manager When Oracle EBS concurrency prompts invalid status, you can restart the concurrency manager to solve the current problem Steps: Access to the AP server of the current environment through terminal software; Input commandcd $ADMIIN_SCRIPTS_HOME, enter the script path; Input commandls, confirm that the script exists in the current pathadcmctl.sh ; […]

  • Mongodb Basics

    Time:2020-1-21

    Micro services are popular. I also like mongodb more and more. Unless MySQL is necessary, I prefer mongodb. MongoDB What is MongoDB? Mongodb is written in C + +, which is an open source database system based on distributed file storage. In the case of high load, adding more nodes can guarantee the server performance. […]

  • Redis must know API

    Time:2020-1-21

    Some nonsense 1. Redis is an open-source, key based storage system with multiple data structures and functions.2. Redis supports persistence, does not lose data after power failure, and asynchronously saves data updates to disk.3. Redis supports string, hash, list, set, ordered set, bitmap, unique count of ultra small memory, and geographic information positioning.4. Redis supports […]