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MS SQL

Posted Jun 3, 2005

SQL Server 2005 System Tables and Views

By Don Schlichting

This article will explore various options for obtaining SQL 2005 metadata information.

Introduction

When a SQL Server object is created, its properties are called metadata. The metadata is stored in special System Tables. For example, in SQL 2000, when a new column was created, the column name and data type could be found in an internal System Table called syscolumns. All SQL objects produce metadata. Every time SQL 2000 Enterprise Manager or SQL 2005 SQL Server Management Studio is browsed, the information displayed about database, tables, and all objects, comes from this metadata. There are many uses for this metadata, including gathering performance statistics, discovering table and column similarities and differences during a database upgrade, and obtaining lock information. In previous versions of SQL Server, these System Tables were exposed and could be queried like any standard table. However, starting with SQL 2005, System Tables are hidden and they cannot be directly queried. Even with full DBA rights, System Tables are restricted. Although not directly accessible, there are built in views and procedures for extracting metadata. Some of these are new in SQL 2005; others were carried forward from pervious versions. Most have the advantage of being more readable and self-describing than querying System Tables. If you have legacy scripts directly referencing System Tables, there are many new System Views that will directly take their place.

System Views

System Views are predefined Microsoft created views for extracting SQL Server metadata. There are over 230 various System Views. To display all the views in SQL 2005, launch the SQL Management Studio; expand Databases, System Databases, and select master, Views, System Views.

These System Views will be automatically inserted into any user created database. The System Views are grouped into several different schemas. In SQL 2005, schemas are used as security containers. There can be several different schemas inside a single database. This is a better ANSI implementation of schemas compared to their use in SQL 2000. See Marcin Policht's excellent article; SQL Server 2005 Security, at http://www.databasejournal.com/features/mssql/article.php/3481751 for a detailed explanation of SQL 2005 schemas and security.

Information Schema

The first group of System Views belongs to the Information Schema set. Information Schema is an ANSI specification for obtaining metadata. There are twenty different views for displaying most physical aspects of a database, such as table, column, and view information.

Information Schema views were available in SQL 2000 and should continue to appear in future versions of SQL. They are a few ANSI terms that translate differently in SQL. An ANSI "Catalog" is a SQL "Database"; an ANSI "RowVersion" is a SQL "Timestamp"; and an ANSI "Timestamp" is a SQL "DateTime." Aside from this, Information Schema views are easy to implement. For an example, we will create a small table with a few columns.

CREATE DATABASE Test
GO
USE Test
GO
CREATE TABLE MyTable
(
Col1 int,
Col2 varchar(10),
Col3 datetime
)
GO

To use Information Schema views, select them like any standard view. The following TSQL will display column and table information on the new database;

SELECT *
FROM INFORMATION_SCHEMA.TABLES

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

Most of the Information Schema view names are self-explanatory. INFORMATION_SCHEMA.TABLES returns a row for each table. INFORMATION_SCHEMA.COLUMNS returns a row for each column. A few though, refer to ANSI names. INFORMATION_SCHEMA.COLUMN_DOMAIN_USAGE contains a row for each column created with a user-defined type, and INFORMATION_SCHEMA.DOMAIN lists a row for each user-defined type. INFORMATION_SCHEMA.ROUTINES shows a record for each stored procedure or function. A benefit to Information Schema views is that because they are an ANSI standard, you will find them in many other database packages.



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