Variable "<str>" is declared CONSTANT - assignment not allowed

  Explanation:  The named variable was declared with the CONSTANT
  keyword which indicates that it should not be changed within the
  scope of this compound statement.  This variable is the target
  of a SET, INSERT...RETURNING, SELECT...INTO, UPDATE...RETURNING,
  or GET GIAGNOSTICS statement or CALL output parameter.

  User Action:  Check that the correct variable is used in this
  statement