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From GeneXus 8.0 RC: Option Distinct Clause

The Option Distinct Clause in the For Each commands enables the retrieval of records with unique values from the referenced attributes.

Scope
Languages: Microsoft .NET, C/SQL, Visual Basic, Visual FoxPro, Java, PocketPC
DBMSs: DB2 UDB for iSeries, DB2 Universal Database, Informix, Oracle, SQL Server, PostgreSQL

Description
In some cases, it is necessary to obtain different values from a set of attributes. This can be worked out by using a control break, through the relevant attributes. In order to solve this in a more efficient way, the option distinct clause has been added to the For Each and XFor Each commands.

For example, suppose there is a table of Persons:

PerCod* Code
PerNam Name
PerEmail Email address
The way to obtain all the different e-mail addresses, without duplicates, is the following:

For Each
Option Distinct
         &email = PerEmail
Endfor

In order to determine the set of different values, the attributes referenced in the For each are taken into account.

General considerations
- The Option Distinct clause in For Each commands is supported by the Client/Server generators and does not apply to local tables.
- For Each commands with option distinct clauses cannot update the database. The same applies for internal For Each commands in control breaks. For Each commands nested in other tables can be updated.
- If an order is not specified, Order None prevails.
- The Option Distinct clause is supported in the "external" For Each commands with control breaks. The "internal" For Each commands inherit the Distinct Clause.
- NULLs are treated as any other value. This means that if a referenced attribute has a DBMS NULL value in more than one record, the For Each command will only retrieve one of them.

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