ASA SQL User's Guide
  Working with Database Objects
    Working with tables
      Working with computed columns

Inserting and updating computed columns

Computed columns restrict the allowed INSERT and UPDATE statements.

• No direct inserts or updates    You cannot insert a value directly into a computed column. If the column called Computed is a computed column, the following statement fails with a Duplicate Insert Column error:

  -- Incorrect statement
  INSERT INTO T1 (id, computed)
  VALUES( 3006, 'bad insert statement' )

  Similarly, you cannot use UPDATE statements to directly change the value of a computed column.

• Listing column names    You must always explicitly specify column names in INSERT statements on tables with computed columns.

• Triggers    If you define triggers on a computed column, any INSERT or UPDATE statement that affects the column fires the triggers.