Considerations regarding inserting into, and updating, computed columns include the following:
Direct inserts and updates You should not use INSERT or UPDATE statements to put values into computed columns since the values may not reflect the intended computation. Also, manually inserted or updated data in computed columns may be changed later when the column is recomputed.
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.
Although you can use INSERT, UPDATE, or LOAD TABLE statements to insert values in computed columns, this is neither the recommended nor intended application of this feature. The LOAD TABLE statement permits the optional computation of computed columns, which can aid the DBA during complex unload/reload sequences, or when it is vital that the value of a computed column stay constant when the COMPUTE expression refers to non-deterministic values, such as CURRENT TIMESTAMP.