• 100 MySQL interview questions for Linux operation and maintenance (3)


    Next: 100 MySQL interview questions for Linux operation and maintenance (2) 001: please explain the concept and main features of relational database? Relational database model is to reduce the complex data structure to simple binary relationship, and the operation of data is to establish one or more relational tables The biggest feature is a two-dimensional […]

  • Notes on SQL multi condition fuzzy query, in, custom function (1)


    Some problems encountered in the work about SQL query, sort out the records, and implement the environment sqlservice 2014 1、 On the same field, several ways to query multiple keywords Basic grammar: SELECT column_name(s) FROM table_name WHERE column_name LIKE pattern Tbuser: Id LastName FirstName 1 Adams John 2 Bush George 3 Carter Thomas   Query […]

  • Query SAP multiple database table sizes


    Query SAP multiple database table sizes https://www.cnblogs.com/ken-yu/p/12973009.html Item code db02 Here are two approaches, In the first graphical interface, the results of the query data table are displayed in MB, and only one table can be queried at a time. SPACE—Segments—Detailed Analysis—Detailed Analysis  In the pop-up window segment / object, enter the name of the […]

  • Lock [implementation of InnoDB isolation]


    Global lock Table level lock Row level lock The locks in MySQL can be roughly divided into global locks, table level locks and row locks. Global lock and table lock are server level, row level lock is storage engine level, only InnoDB supports row and lock. Global lock: It is to lock the entire database […]

  • Constructors in Java child parent classes


    When the subclass object is initialized, the constructor of the parent class also runs, That’s because the default first line of the subclass constructor has an implicit statement: super(); Super (): will access the null parameter constructor in the parent class. Moreover, the default first line of all constructors in the subclass is: super(); Why […]

  • MySQL learning — managing user rights


    MySQL learning — managing user rights Absrtact: This paper mainly studies the method of using DCL statement to manage user rights. Understanding user rights What is a user Users refer to the people who operate and use MySQL database. Using MySQL database requires users to connect through user name and password before operation. Different users […]

  • Delete table and Oracle recycle bin


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

  • MySQL performance analysis memo


    [TOC] Last revision time: 15:08:59, October 21, 2019 Emergency show full processlist Check the current thread processing, confirm which statements are executing and how the execution is Special attention should be paid to those with long execution time. If problems are identified, they can be usedkill {id}Kill the connection show full processlistEquivalent to the following […]

  • The calculation of self attention in Bert series


    Best is based on transformer, and one of the core modules of transformer is self attention. Here, we will introduce self attention and its calculation process in detail; 1、 What is self attention? The animal didn’t cross the street because it was too tiredFor example, in the sentence above, it is easy to see what […]

  • Using database trigger to realize data synchronization


    1、 What is a trigger A database trigger is a stored PL / SQL statement associated with a table. Whenever a specific data operation statement (insert update delete) is issued on the specified table, Oracle automatically executes the statement sequence defined in the trigger. The application scenarios of triggers are as follows: Complex security checks […]

  • Common SQL Server Performance Optimization statements


    1. Lock monitoring To view a locked table: select request_session_id spid,OBJECT_NAME(resource_associated_entity_id) tableName from sys.dm_tran_locks where resource_type=’OBJECT’ To see which session is blocking and what they are running: SELECT DTL.[request_session_id] AS [session_id] , DB_NAME(DTL.[resource_database_id]) AS [Database] , DTL.resource_type , CASE WHEN DTL.resource_type IN ( ‘DATABASE’, ‘FILE’, ‘METADATA’ ) THEN DTL.resource_type WHEN DTL.resource_type = ‘OBJECT’ THEN OBJECT_NAME(DTL.resource_associated_entity_id, […]

  • True value, false value and pit in openresty


    First review the true and false values in Lua: all values are true except nil and false. The concept of “other values” includes 0, empty string, empty table, and so on.In Lua, it is commonly usedandandorAs a logical operator. such astrue and falsereturnfalse, andfalse or truereturntrue。 OK, that’s the end of the review. Let’s take […]