Logical View Limitations

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In many respects, a Logical View behaves in the same way as a Table. In USoft Windows Designer and Web Designer, you get default info windows and info pages for Logical Views in the same way as for Tables.

But Logical Views have limitations that Tables do not have.

Limitations in SQL

The SQL constructs you can use to define a Logical View are limited:

You cannot use ORDER BY, CONNECT BY or START WITH clauses.

You cannot use the UNION, INTERSECT and MINUS set operators. Only UNION ALL is allowed.

You cannot use CONNECT BY or START WITH clauses.

A Logical View's SQL Statement may contain joins, subqueries, WHERE, HAVING and GROUP BY clauses, and SQL functions.

Limitations in model structure

A Logical View:

Cannot be used as the Parent Object or Child Object of a Relationship.

Cannot be a supertype or subtype.

Cannot be the Transition Table of a Constraint.

Limitations in data manipulation options

By default, Logical Views cannot freely manipulate data in the same way as Tables. See the help topic on data manipulation through Logical Views for details.

However, you can customise data manipulation through Logical Views by using rule-based logical views.

No Update Notify

Update Notify is the standard USoft behavior in C/S applications that data on the screen is refreshed if that data is updated by the Rules Engine. Update Notify is NOT supported on multi-table Logical Views; the user or the application must re-query to get the new data in view.

The fact that Update Notify is not supported on multi-table Logical Views can lead to unexpected results on the screen if the same underlying column is used multiple times in the Logical View's SELECT list.

See Also

How to Define Logical Views

Checking Logical Views

Data Interaction through Logical Views

Logical View column attributes

Rule-based Logical Views