techats

Oracle 10g Architechture Oracle have two main componenets: 1. Instance (Memory) 2. Database (Physical datafiles) One instance for one database. Instance Consists of: SGA and Background Processes       1. SGA - System Global Area                    1.Shared Pool                          1.Data Dictionary Cache                          2. Library Cache                                   1.SQL Area           ...

Why not null constraint cannot be applied at the table level?? Ans:  All Constraint  gives the logical view to that particular column but NOT NULL get assigned to the structure of the table itself, that's why we see NOT NULL constraint while Describe command is issued against the table and no other constraint will be seen. So all the constraints can be applied at table level and column level except NOT NULL that can be acheived only at the column level and not at the table level