Restrictions for UPDATE Statements 

For UPDATE statements and SELECT statements that contain an UPDATE clause, the following restriction applies to the use of search conditions:

If the new value of a column is calculated in an arithmetical expression, an inversion of this column, that is, the corresponding index, cannot be evaluated by the SQL Optimizer to determine the search strategy .

UPDATE <table_name>
  SET columnx = columnx + 3
    WHERE columnx IN (100, 103, 106, 109, 112)

This SQL statement could lead to errors in the results if the inversion lists were processed step-by-step with the values 100, 103, 106, 109, and 112.

See also:

SQL Reference Manual, UPDATE Statement (update_statement), UPDATE Clause (update_clause)