C.1 Data Dictionary Support

The following topics describe the Oracle Database Gateway for SQL Server data dictionary support.

• SQL Server System Tables
  SQL Server data dictionary information is stored in the SQL Server database as SQL Server system tables.
• Accessing the Gateway Data Dictionary
  Accessing a gateway data dictionary table or view is identical to accessing a data dictionary in an Oracle database.
• Direct Queries to SQL Server Tables
  Queries issued directly to individual SQL Server system tables are allowed but they return different results because the SQL Server system table column names differ from those of the data dictionary view.
• Supported Views and Tables
  The Oracle Database Gateway for SQL Server supports the following views and tables.

C.1.1 SQL Server System Tables

SQL Server data dictionary information is stored in the SQL Server database as SQL Server system tables.

All SQL Server system tables have names prefixed with sys. The SQL Server system tables define the structure of a database. When you change data definitions, SQL Server reads and modifies the SQL Server system tables to add information about the user tables.

C.1.2 Accessing the Gateway Data Dictionary

Accessing a gateway data dictionary table or view is identical to accessing a data dictionary in an Oracle database.

You issue a SQL SELECT statement specifying a database link. The Oracle database data dictionary view and column names are used to access the gateway data dictionary in an Oracle database. Synonyms of supported views are also acceptable. For example, the following statement queries the data dictionary table ALL_CATALOG to retrieve all table names in the SQL Server database:

SQL> SELECT * FROM "ALL_CATALOG"@MSQL;

When a data dictionary access query is issued, the gateway:

1. Maps the requested table, view, or synonym to one or more SQL Server system table names. The gateway translates all data dictionary column names to their corresponding SQL Server column names within the query. If the mapping involves one SQL Server system table, the gateway translates the requested table name to its corresponding SQL Server system table name within the query. If the mapping involves multiple SQL Server system tables, the gateway constructs a join in the query using the translated SQL Server system table names.
2. Sends the translated query to SQL Server.
3. Might convert the retrieved SQL Server data to give it the appearance of the Oracle database data dictionary table.
4. Passes the data dictionary information from the translated SQL Server system table to the Oracle database.

   Note:

   The values returned when querying the gateway data dictionary might not be the same as the ones returned by the Oracle SQL*Plus DESCRIBE command.

C.1.3 Direct Queries to SQL Server Tables

Queries issued directly to individual SQL Server system tables are allowed but they return different results because the SQL Server system table column names differ from those of the data dictionary view.

Also, certain columns in an SQL Server system table cannot be used in data dictionary processing.

C.1.4 Supported Views and Tables

The Oracle Database Gateway for SQL Server supports the following views and tables.

ALL_CATALOG	ALL_COL_COMMENTS
ALL_CONS_COLUMNS	ALL_CONSTRAINTS
ALL_IND_COLUMNS	ALL_INDEXES
ALL_OBJECTS	ALL_TAB_COLUMNS
ALL_TAB_COMMENTS	ALL_TABLES
ALL_USERS	ALL_VIEWS
DBA_CATALOG	DBA_COL_COMMENTS
DBA_OBJECTS	DBA_TAB_COLUMNS
DBA_TAB_COMMENTS	DBA_TABLES
DICT_COLUMNS	DICTIONARY
DUAL	TABLE_PRIVILEGES
USER_CATALOG	USER_COL_COMMENTS
USER_CONS_COLUMNS	USER_CONSTRAINTS
USER_IND_COLUMNS	USER_INDEXES
USER_OBJECTS	USER_TAB_COLUMNS
USER_TAB_COMMENTS	USER_TABLES
USER_USERS	USER_VIEWS

No other Oracle database data dictionary tables or views are supported. If you use a view not on the list, you will receive the Oracle database error code for no more rows available.

Queries through the gateway of any data dictionary table or view beginning with ALL_ can return rows from the SQL Server database even when access privileges for those SQL Server objects have not been granted. When querying an Oracle database with the Oracle data dictionary, rows are returned only for those objects you are permitted to access.