[ @name ] = { 'property_name' }

Is the name of the property to be added. property_name is sysname and cannot be NULL. Names can also include blank or non-alphanumeric character strings, and binary values.

[ @value = ] { 'value' }

Is the value to be associated with the property. value is sql_variant, with a default of NULL. The size of value cannot be more than 7,500 bytes.

[ @level0type = ] { 'level0_object_type' }

Is the type of level 0 object. level0_object_type is varchar(128), with a default of NULL.

Valid inputs are ASSEMBLY, CONTRACT, EVENT NOTIFICATION, FILEGROUP, MESSAGE TYPE, PARTITION FUNCTION, PARTITION SCHEME, REMOTE SERVICE BINDING, ROUTE, SCHEMA, SERVICE, USER, TRIGGER, TYPE, and NULL.

Important:
USER and TYPE as level-0 types will be removed in a future version of SQL Server. Avoid using these features in new development work, and plan to modify applications that currently use these features. Use SCHEMA as the level 0 type instead of USER. For TYPE, use SCHEMA as the level 0 type and TYPE as the level 1 type.

[ @level0name = ] { 'level0_object_name' }

Is the name of the level 0 object type specified. level0_object_name is sysname with a default of NULL.

[ @level1type = ] { 'level1_object_type' }

Is the type of level 1 object. level1_object_type is varchar(128), with a default of NULL. Valid inputs are AGGREGATE, DEFAULT, FUNCTION, LOGICAL FILE NAME, PROCEDURE, QUEUE, RULE, SYNONYM, TABLE, TABLE_TYPE, TYPE, VIEW, XML SCHEMA COLLECTION, and NULL.

[ @level1name = ] { 'level1_object_name' }

Is the name of the level 1 object type specified. level1_object_name is sysname, with a default of NULL.

[ @level2type = ] { 'level2_object_type' }

Is the type of level 2 object. level2_object_type is varchar(128), with a default of NULL. Valid inputs are COLUMN, CONSTRAINT, EVENT NOTIFICATION, INDEX, PARAMETER, TRIGGER, and NULL.

[ @level2name = ] { 'level2_object_name' }

Is the name of the level 2 object type specified. level2_object_name is sysname, with a default of NULL.

0 (success) or 1 (failure)

For specifying extended properties, the objects in a SQL Server database are classified into three levels: 0, 1, and 2. Level 0 is the highest level and is defined as objects that are contained at the database scope. Level 1 objects are contained in a schema or user scope, and level 2 objects are contained by level 1 objects. Extended properties can be defined for objects at any of these levels.

References to an object in one level must be qualified with the names of the higher level objects that own or contain them. For example, when you add an extended property to a table column (level 2), you must also specify the table name (level 1) that contains the column and the schema (level 0) that contains the table.

For a complete list of objects and their valid level 0, 1, and 2 types, see Using Extended Properties on Database Objects.

If all object types and names are null, the property belongs to the current database itself.

Extended properties are not allowed on system objects, objects outside the scope of a user-defined database, or objects not listed in Arguments as valid inputs.

Replicating Extended Properties

Schema vs. User

Members of the db_owner and db_ddladmin fixed database roles can add extended properties to any object with the following exception: db_ddladmin cannot add properties to the database itself, or to users or roles.

Users can add extended properties to objects they own or have ALTER or CONTROL permissions on. For a complete list of required permissions, see Using Extended Properties on Database Objects.

A. Adding an extended property to a database

USE AdventureWorks;
GO
--Add a caption to the AdventureWorks Database object itself.
EXEC sp_addextendedproperty 
@name = N'Caption', @value = 'AdventureWorks Sample OLTP Database';

B. Adding an extended property to a column in a table

USE AdventureWorks;
GO
EXEC sp_addextendedproperty 
@name = N'Caption', @value = 'Postal code is a required column.',
@level0type = N'Schema', @level0name = Person,
@level1type = N'Table',  @level1name = Address,
@level2type = N'Column', @level2name = PostalCode;
GO

C. Adding an input mask property to a column

USE AdventureWorks;
GO
EXEC sp_addextendedproperty 
@name = N'Input Mask ', @value = '99999 or 99999-9999 or #### ###',
@level0type = N'Schema', @level0name = Person,
@level1type = N'Table', @level1name = Address, 
@level2type = N'Column',@level2name = PostalCode;
GO

D. Adding an extended property to a filegroup

USE AdventureWorks;
GO
EXEC sys.sp_addextendedproperty 
@name = N'MS_DescriptionExample', 
@value = N'Primary filegroup for the AdventureWorks sample database.', 
@level0type = N'FILEGROUP', @level0name = [PRIMARY];
GO

Reference

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