连接到服务器vs连接到数据库

Question

What's the difference between connecting to a server as opposed to connecting to a database?

The context of the question is that I'm in charge of developing a proof of concept where a user can select one of our servers, a database within that server, a table within that database, and a column within that table. I am using Visual C# and ASP.NET. I believe I can get the servers from the connection strings in the web.config, but I'm not quite sure how.

If it helps at all (I do like examples), you can assume SQL servers.

Answer 1

(Answer to original question)

There is a hierarchy:

• Server : A piece of physical (or virtual) hardware that runs an OS and applications. You will address it via IP address or DNS name, in can host multiple Database Servers
  • Database Server (aka Instance) : A piece of software that runs that can host multiple Databases. when you use a connection string it is in the format "ServerName\\InstanceName"
    • Database : A data structure that can host multiple Data Tables
      • Data Table : A data structure that can host multiple Columns and Rows
        • Column : The smallest division of information seperation, holds information about a specific topic
        • Row : Holds a single set of columns.

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(Answer to updated question)

It is different per SQL provider, but using Microsleft SQL server you just connect to the server (don't provide a default instance in the connection string) and do the following:

select * from sys.databases 

Once you have your database, connect to that database and do the following to get the tables

select * from sys.tables where type = 'U'

to get the columns you do

select * from sys.Columns

however to get the name of the table the column is in you need to match Object_id to Object_id on sys.tables

select t.name as TableName, c.Name as ColumnName  
from sys.tables t
inner join sys.columns c on t.object_id = c.object_id
where t.Type = 'U'

Answer 2

You can achieve your goal. Initially, you would connect to database master on the server and query the databases on that server.

SELECT * FROM sys.databases

Then, you would initiate a new connection to the selected database and query that database's information schema, to get a list of tables.

SELECT * FROM INFORMATION_SCHEMA.TABLES

Repeat for selecting a column.

SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'foo'

Answer 3

如果服务器是指数据库服务器，则应连接到服务器以访问该服务器上托管的数据库。