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

When computed columns are recalculated

Computed columns are recalculated under the following circumstances:

• Any column is deleted, added, or renamed.

• The table is renamed.

• Any column's data type or COMPUTE clause is modified.

• A row is inserted.

• A row is updated.

Computed columns are not recalculated when queried. If you use a time-dependent expression, or one that depends on the state of the database in some other way, then the computed column may not give a proper result.