in http://docs.oracle.com/cd/B19306_01/server.102/b14200/statements_8004.htm The view must not contain any of the following constructs: A subquery in a SELECT list.
but this works
"UPDATE (SELECT employee_id, salary, (SELECT 'sub' FROM DUAL) sub FROM employees) SET salary = 1" In addition, if an inherently updatable view contains pseudocolumns or expressions, then you cannot update base table rows with an UPDATE statement that refers to any of these pseudocolumns or expressions.
but including ROWNUM pseudocolumn doesnt work
"UPDATE (SELECT employee_id, salary, ROWNUM no FROM employees) SET salary = 1"
in http://docs.oracle.com/cd/E11882_01/server.112/e26088/statements_3001.htm#SQLRF53384 You can change a CHAR column to VARCHAR2 (or VARCHAR) and a VARCHAR2 (or VARCHAR) column to CHAR only if the BLANK_TRIMMING initialization parameter is set to TRUE and the column size stays the same or increases.
but i can modify a columns datatype between char and varchar2 without setting blank_trimming to true?