Because USL links heterogenous systems, overall performance is affected by processes taking place on the USL Portal Server, on Teradata Database, and on the foreign database.

In addition to connecting Teradata Database to a foreign database, one of the main functions of the USL Portal Server is to process any required data conversions between the two systems. This means Teradata Database is relieved of the burden of data conversions, aiding in overall system performance when processing data from the foreign database.

USL uses two different SQL database engines, making it important to understand which portions of a query are executed by which database engine.

This scenario illustrates a heterogeneous join.

A company owns multiple casino properties. One casino (C1) is in Las Vegas and the other (C2) is in Atlantic City. A customer walks into the Las Vegas property and uses their loyalty card. The management wants to know the customer's status but they only have activity data on their customers. They query the activity data from other casino properties as well as their own. The problem is that the different casino properties are somewhat independent and use different database vendors. Las Vegas uses Teradata Database and Atlantic City uses a foreign database. In this simple scenario they are looking for the customer's last activity date and total winnings in all past visits.

This scenario assumes the following tasks have already been performed by the system and Unity Source Link administrators:

• The External Access Handler software has been installed on Teradata Database.
• Appropriate access rights to DBCForeign have been granted to the Unity Source Link Administrator, and the USL administrator has granted appropriate access rights to users who require access to USL.
• The Unity Source Link Portal Server service has been started and configured.
• A portal that defines the Teradata Database connection to the foreign database has been created. The portal must use the same port number as that used by the service (the default is port 5678).
• ODBC data sources have been created on the Unity Source Link Portal Server (a Teradata Managed Server) to access the foreign database. In our scenario, the foreign database is Oracle.
• Teradata Wallet has been configured to store and protect the Oracle Database passwords in an encrypted form.

Our scenario will show how a Teradata Database user with appropriate privileges can access the data in both the Teradata and Oracle databases to answer questions about casino guests.

Assume the following customer data exists in the Teradata database table c1 for the Las Vegas casino:

Assume the following customer data exists in the Oracle database table Datatypes.c2 for the Atlantic City casino:

USL allows you to create links to foreign databases. These links are views in DBCForeign that you can query the same way that you query tables and views in Teradata Database.

1. Use the CreateLink command to define a link in Teradata Database to a table in a foreign database to create a view for this table in the DBCForeign database. Example:

   CALL DBCForeign.CreateLink('LinkName', 'TableName', 'ServerName', 'SelectList', 'Clause', outStatus);

   Option	Description
   LinkName	Name of the link. The view that gets created takes the form of "LinkName@ServerName'".
   TableName	Name of the foreign table to be accessed, up to 128 characters.
   ServerName	Name of a server that was previously created using the CreateServer stored procedure. A list of the created servers can be obtained by querying the DBCForeign.Servers table.
   SelectList	[Optional] List of foreign table columns to be selected. If no select list is specified, all foreign table columns are selected. The list is not limited to a simple list of columns. SQL must be well-formed. It can contain the following operations and functions: scalar operations, such as c1 + 10 aggregate functions non-aggregate columns, must appear in a GROUP BY clause user defined functions
   Clause	[Optional] SQL clause to specify filtering, grouping, or ordering operations that are performed on the table. If no clause is specified, no filtering, grouping, or ordering operations are performed on the table. The WHERE keyword is not needed if the clause only contains a WHERE clause. c3 > 10 c3 > 10 GROUP BY c1 c3 > 10 GROUP BY c1 GROUP BY c1
   outStatus	Returns a message indicating the stored procedure executed successfully or an error occurred.

1. Login to the USL portal server and use a SQL client to create the link.

   CALL DBCForeign.CreateLink('c2Link2', 'Datatypes.c2', 
   'Connect2Oracle', 'Cust_ID, MAX(Activity_DT) dt, 
   SUM(Tot_Dollars) td', 'GROUP BY Cust_ID', st);
   
   *** Procedure has been executed. 
   *** Total elapsed time was 3 seconds.
   
   
   outStatus
   ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
   [USL7109] OK! User =  DATATYPES_USER1, Select List = "Cust_ID, MAX(Activity_DT) dt, SUM(Tot_Dollars) td", Clause = "GROUP BY Cust_ID", View = "c2Link2@Connect2Oracle"
   
   SHOW VIEW DBCForeign."C2Link2@Connect2Oracle";
   
   *** Text of DDL statement returned. 
    *** Total elapsed time was 1 second.
   
   ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
   CREATE VIEW "DBCForeign"."c2Link2@Connect2Oracle" AS (SELECT * FROM "DBCForeign"."Import" (
   USING 
   I_TABLE('Datatypes.c2') 
   I_SQL('SELECT Cust_ID, MAX(Activity_DT) dt, SUM(Tot_Dollars) td 
   FROM Datatypes.c2 
   GROUP BY Cust_ID')
   I_PORTAL_IP('153.64.25.217')
   I_PORT( 5005) 
   I_DATASOURCE('oracle') 
   I_DSN('OracleWP') 
   I_TIMEOUT(    20) 
   I_UID('datatypes_user1') 
   I_PWD('$tdwallet')) AS I1)
   

1. Run a query.

   SELECT Cust_ID (TITLE 'Customer'),
          MAX(dt) (TITLE 'Last Visit'),
          SUM(td) (TITLE 'Winnings')
   FROM (SELECT Cust_ID, MAX(Activity_DT) dt, SUM(Tot_Dollars) td
         FROM c1 
         GROUP BY 1
         UNION
         SELECT Cust_ID, dt, td
         FROM DBCforeign."c2Link2@Connect2Oracle" 
        ) c
   GROUP BY 1
   WHERE Cust_ID = 3;
   

   The new query returns one row:

     Customer  Last Visit  Winnings
   -----------  ----------  --------
             3    13/01/02   1500.00
   

Notice that the query selects information from both the Teradata database table holding the Las Vegas customer information and the view of the Oracle database table data holding the Atlantic City customer information. The necessary data transformation is taken care of automatically by USL so the information can be combined and manipulated seamlessly by Teradata Database.

The SELECT statement immediately above the UNION collects the Las Vegas data in a table c1. That SELECT statement aggregates the table data per customer to show the most recent casino visit date and the sum of all the money won or lost by the customer up to and including that date. By itself, that SELECT would return this data:

The SELECT statement immediately after the UNION queries the view of the Oracle data. This view was created in Teradata Database. Because the link statement specified similar aggregations on the Oracle data, this SELECT statement would return data organized in similar columns to the data above:

That data in the original Oracle table might have looked like this before USL transformed it to match the data formats used in Teradata Database:

The complete query that combines data from both the Las Vegas and Atlantic City casinos uses a WHERE clause to limit the data to the customer of interest, and mathematically sums the customer's winnings from both casinos to present the overall grand total amount won or lost by that customer at both casino locations: