Rules for updatable query expressions

A query expression is updatable if the following conditions are fulfilled:

• The query expression does not contain a join expression.

• The query expression does not contain a UNION or EXCEPT operation.

• Only column names can be specified in the SELECT list. Other elements of an expression, e.g. subqueries, function calls or literals, are not permitted. Atomic columns cannot be specified more than once. Subareas from multiple columns cannot overlap.

• Only a table or updatable subquery can be specified in the FROM clause. If a table is specified, it must be a base table or an updatable view.

• No subquery can occur in the WHERE clause.

• The keyword DISTINCT cannot be specified.

• The SELECT expression cannot include a GROUP BY or HAVING clause.