Transaction log - Definition - Database

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• Nirja Shah   -Posted on 03 Nov 15
  Transaction logs
  - Transaction logs are a vital yet often overlooked component of database architecture.
  - They are often forgotten because they are not something actively maintained like the schema contained within a database.
  - In this article we’ll examine how transaction logs are used in Microsoft SQL Server, maintenance and potential problems with them, how they can be used to restore a database, and finally, optimizing them for performance.
  
  Query language
  - Data Query Language is used to extract data from the database. It doesn't modify any data in the database. It describes only one query: SELECT.
  
  DML
  - Data Manipulation Language (DML) statements are used for managing data within schema objects. Some examples:
  
  - SELECT - It retrieves data from the a database
  - INSERT - It inserts data into a table
  - UPDATE - It updates existing data within a table
  - DELETE - It deletes all records from a table, the space for the records remain
  - MERGE - The UPSERT operation (insert or update)
  - CALL - It calls a PL/SQL or Java subprogram
  - EXPLAIN PLAN - It explains the access path to data
  - LOCK TABLE - It controls concurrency
  
  Report writer
  - It is also known as a report generator, it is a program, which usually is a part of a database management system, that extracts information from one or more files and presents the information in a specified format.
  - Most of the report writers allows you to select the records that meet certain conditions and to display selected fields in rows and columns.
  - You can also format data into pie charts, bar charts, and other diagrams.
  - Once you have created a format for a report, you can save the format specifications in a file and continue reusing it for new data.
  

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