Microsoft SQL Server 2008 Technology Insider T-SQL Language Foundation Chapter 1th T-SQL query and Programming fundamentals

System databases include:

Master Master Data holds metadata information, server configuration, information about all databases in the instance, and initialization information in SQL Server instance scope

Resource The resource database is added in SQLServer2005 to hold all system objects. When querying metadata information in a database, this information is ostensibly in the database, but is actually saved in the resource database

The model model database is a template for the new database. Each newly created database is initially a copy of the model. So, if you want to include specific objects (such as data types) in all newly created databases, Or, if you configure some database properties in a specific way in all newly created databases, you can put these objects or configuration properties in the model database first. Note: Modifications made to the model database do not affect existing databases, only the newly created database after

The tempdb tempdb database is where SQL Server holds temporary data, including worksheets (work table), sort spaces, row versioning (row versioning) information, and so on. SQL Server allows users to create temporary tables for their own use, where the physical location of these temporary tables is tempdb. Note: Each time the SQL Server instance is restarted, the contents of the database are deleted and recreated as a copy of the model. Therefore, When you need to create objects for testing purposes, and you do not want to keep them in the database after testing is complete, you can usually create them in tempdb. Even if you forget to clear these objects, they are automatically cleared after a restart.

msdb msdb is the place where a service called SQLServerAgent holds its data. SQLServerAgent is responsible for automating processing, including recording information about entities such as job (Job), schedule (schedule), and alerts. SQLServerAgent is also responsible for replicating (replication) services. Msdb is also used to hold some information about other SQL Server features, such as database Mail and Service Broker

Microsoft SQL Server 2008 Technology Insider T-SQL Language Foundation Chapter 1th T-SQL query and Programming fundamentals