INFORMATIONSCHEMA

INFORMATION_SCHEMA

Introductions
When we are taking about any RDBMS, it should be a data dictionary or metadata. MS SQL Server has no exceptions.
In MS SQL Server there are two sources to view the metadata information.  
1.    Various System Tables
2.    INFORMATION_SCHEMA views
In this article I am trying to discuss about the INFORMATION_SCHEMA.
Point to Focus
1.    Metadata
2.    Anything wrong to pull information from system table
3.    About INFORMATION_SCHEMA view
4.    Descriptions of views
5.    Using INFORMATION_SCHEMA
Metadata
First we understand that what metadata is. In common understanding about metadata, we can say that it is “data about data”. In the context of database it means “Information (data) stored about data, the structures or objects related to data”.
Anything wrong to pull information from system table
As per Microsoft, information wise there is no difference but Microsoft reserves the rights to change any system table from version to version. So if an application depends on the system table can face a serious problem due to version change. Is it true? I don’t find such an example in my development career. But we should remember the statutory warning of Microsoft.
About INFORMATION_SCHEMA view
SQL Server makes available the Information Schema Views through INFORMATION_SCHEMA schema. It is available in each database and storing information about all database objects contained in the respective database.  The following query is used to retrieve the views available under the INFORMATION_SCHEMA schema and their definitions.
SELECT s.name [Schema_Name],
       o.name [Object_Name],
       sm.definition [Schema_Defination]
FROM   sys.all_sql_modules sm
       INNER JOIN sys.all_objects o ON sm.object_id = o.object_id
       INNER JOIN sys.schemas s ON o.schema_id = s.schema_id
WHERE  s.name = ‘INFORMATION_SCHEMA’
ORDER BY o.name;
Here most of the views names are self describing.
Descriptions of Views
Here are the lists of views and there descriptions are mentioned bellow. For better understanding please refer to MSDN.
No
View
Description
1.
Returns one row for each CHECK constraint
2.
Returns one row for each column that has an alias data type
3.
Returns one row for each column that has a privilege that is either granted to or granted by
4.
Returns one row for each column
5.
Returns one row for each column that has a constraint defined on it
6.
Returns one row for each table that has a constraint defined on it
7.
Returns one row for each alias data type that has a rule bound to it
8.
Returns one row for each alias data type
9.
Returns one row for each column that is constrained as a key
10.
Returns one row for each parameter of a user-defined function or stored procedure
11.
Returns one row for each FOREIGN KEY constraint
12.
Returns one row for each stored procedure and function
13.
Returns one row for each column returned by table-valued functions
14.
Returns one row for each schema
15.
Returns one row for each table constraint
16.
Returns one row for each table privilege that is granted to or granted by
17.
Returns one row for each table
18.
Returns one row for each column that is used in a view definition
19.
Returns one row for each table that is used in a view
20.
Returns one row for views

Using INFORMATION_SCHEMA
Here is the simple example to understand the information schema.
1.  TABLEs

SELECT * FROM information_schema.tables
WHERE TABLE_TYPE = ‘BASE TABLE’;
SELECT * FROM information_schema.tables
WHERE  TABLE_TYPE = ‘BASE TABLE’
       AND table_name = ‘xyz’;
      
SELECT * FROM information_schema.tables
WHERE  TABLE_TYPE = ‘BASE TABLE’
       AND table_name = ‘xyz’
       AND table_schema = ‘abc’;

2.  VIEWs

SELECT * FROM information_schema.tables
WHERE  TABLE_TYPE = ‘VIEW’;


3.  List CONSTRAINTs

it retrieves all the constraints of Table objects “XYZ”


SELECT constraint_name, constraint_type
FROM   INFORMATION_SCHEMA.TABLE_CONSTRAINTS
WHERE  table_name = ‘xyz’;

4.  List FUNCTIONs

SELECT routine_name

FROM   INFORMATION_SCHEMA.ROUTINES
WHERE  routine_type = N’FUNCTION’;

Hope you like it.
Posted by: MR. JOYDEEP DAS

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