Oracle data operation and control language detailed
http://blog.9cbs.net/chensheng913/archive/2004/09/02/92895.aspx
Named of PL / SQL variables:
v_variablename pragram variable
E_EXCEPTIONNAME User-Defined Exception
T_typename User-Defined Type
P_ParameterName Parameter To a Procedure Or Function
C_ConstantValue Variable Constrained with the constant clause
