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Thread: orcle tool

  1. #1
    Join Date
    Feb 2009

    Post Unanswered: orcle tool

    is it oracle a tool or DBMS???
    and what is the difference between
    primary key,
    ( not null and unique imposed on a single column?)
    empno number(30) constraint empno_unique_nn not null unique;
    the enternal structure of blob,clob etc, are these store with the table or outside the table

  2. #2
    Join Date
    Jan 2004
    Croatia, Europe
    Provided Answers: 5
    Oracle 10g documentation. Start with the Concepts book.

  3. #3
    Join Date
    Mar 2007
    From wikipedia:
    An oracle is a source of counsel or prophecy.
    Oracle is also a software company providing many products, e.g. DBMS, tools.

    To your second question, you might be intrested in reading this thread on AskTom:

    Your last statement (as it does not contain question mark) is surely true (as both options are exclusive). Maybe you would benefit from studying "Application Developer's Guide - Large Objects" book, available with other Oracle documentation e.g. online on

  4. #4
    Join Date
    Feb 2009
    for example table containing this
    empno number(3) primary key,
    and another table containng
    deptno number(30 ) constraints deptn_nn_uniq not null unique.

    what is the difference between these two statements?

  5. #5
    Join Date
    Sep 2002
    Provided Answers: 1
    There isn't a lot of difference. A primary key is guaranteed to be unique and not null, which makes it suitable for identifying any and every row in the table. A unique constraint and a not null constraint together achieve the same thing, a little less clearly. And the existence of a primary key prevents you from dropping the NOT NULL constraint - it's a bit safer:
    SQL> create table t1 (id integer primary key, id2 integer not null unique);
    Table created.
    SQL> alter table t1 modify id null;
    alter table t1 modify id null
    ERROR at line 1:
    ORA-01451: column to be modified to NULL cannot be modified to NULL
    SQL> alter table t1 modify id2 null;
    Table altered.
    See also this Ask Tom answer.

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