• Detailed analysis of explain command in MySQL


    In many cases, we need to know the performance of a SQL statement, and we will check how the query optimizer executes through the explain command. How to use it useEXPLAINVery simple, just add theEXPLAINthat will do explain select s.sid sid, s.name studentName, s.age age, c.name className from student_class sc, student s, class c; The […]

  • SQL server queries where to call the stored procedure or table


    When we first started to contact some formed projects, it’s ok if it is not complex. If it is complex, for example, ERP project, in which the business logic is complex, it may be called back and forth between various stored procedures. We can use the –Query where to call the table or stored procedure […]

  • Go learning notes — slice


    Delete the last value of the slicescores := []int{1, 2, 3, 4, 5}lastIndex := len(scores)-1source[:lastIndex]scores = scores[:lastIndex] Create a slice with the bottom array of 10 and length of 0scores := make([]int, 0, 10) //cap=10 len=0//cap=10 , len=3scores := make([]int, 3, 10)scores = append(scores, 1)//Note that the scores are: [0 000 1] Swap the positions […]

  • All parsing of external, terminated, partitioned and stored in the table creation statement of hive


    Starting from the statement of creating tables on the official website, my analysis is as follows: `CREATE [TEMPORARY] [EXTERNAL] TABLE [IF NOT EXISTS] [db_name.]table_name    — (Note: TEMPORARY available in Hive“0.14“.“0“and later)` `[(col_name data_type [column_constraint_specification] [COMMENT col_comment], … [constraint_specification])]` `[COMMENT table_comment]` `[PARTITIONED BY (col_name data_type [COMMENT col_comment], …)]` `[CLUSTERED BY (col_name, col_name, …) [SORTED BY (col_name […]

  • Summary after reading MySQL


    Series articles: Summary after reading MySQL Summary after reading MySQL (2) Summary after reading MySQL (3) How is a SQL query executed? Schematic diagram of MySQL basic architecture MySQL is divided into server layer and storage engine layer The server layer includes connector, query cache, analyzer, optimizer, executor, etc., covering most of the core service […]

  • In mysql, using code farmer is very busy with IP address database


    After downloading to the database of the busy IP address of the code farmer, we can store it in the MySQL database, and when we need to query the location data of an IP, we can get the correct results through SQL statements. This is a very convenient way to use, and after adding the […]

  • As soon as I got on the job, I met such a big bug as MySQL! I almost walked away with the pot on my back


    This year, sometimes I don’t dare to jump if I don’t find a good place to go. I just jumped to my new employer a few days ago. On the day when I started to work, something happened. I was really scared out of a cold sweat (the boss kept staring at me and said […]

  • Data upgrade (synchronization) tool


    Data upgrade tool 1. Why is this tool available? The company’s main products are Oracle database, which is updated every 2 or 3 years.After the new version goes online, it needs to upgrade to the old customers, and the data in the old system must be collected when upgrading.The upgrade of the previous version is […]

  • Java process control: sequential structure


    1、 Process control In JavaProcess control statementIt can be classified as follows:Sequence structure, choice structure and circulation structure。 These three structures are enough to solve all the problems! 2、 Sequential structure Description: Java process controlBasic structureIt’s a sequential structure. Unless otherwise specified, java code isIn order, statements and code blocks are executed from top to […]

  • Interview summary: 10 common interview questions and answers about “MySQL affairs”


    The article is constantly updated every week. It’s not easy to create original articles. It’s my greatest affirmation that “Sanlian” let more people see it. WeChat can search the public for the first time to read the official account of “backend Technology School” (usually one to two updates earlier than blogs). Learning the relational database […]

  • Graphic SQL, this is too image!


    Author Tony, who doesn’t cut her hairSource https://blog.csdn.net/horses/… This paper introduces the design idea of relational database: everything is relational in SQL. There are many great design concepts and ideas in the computer field, such as: In UNIX, everything is a file. In object-oriented programming languages, everything is an object. The same is true of […]

  • Exception handling of JavaScript


    WhenJavaScriptEngine executionJavaScriptCode, there may be a variety of exceptions, such as syntax exceptions, missing features in the language, and exceptions caused by the exception output from the server or user. andJavascriptThe engine is single threaded, so once an exception is encountered,JavascriptThe engine usually stops execution, blocks subsequent code and throws an exception message. Therefore, we […]