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CHAR pads blank spaces to the maximum length. VARCHAR2 does not pad
blank spaces. For CHAR it is 255 and 2000 for VARCHAR2.
18. How many LONG columns are allowed in a table ? Is it possible to
use LONG columns in WHERE clause or ORDER BY ?
Only one LONG columns is allowed. It is not possible to use LONG column
in WHERE or ORDER BY clause.
19. What are the pre requisites ?
I. to modify datatype of a column ?
ii. to add a column with NOT NULL constraint ?
To Modify the datatype of a column the column must be empty.
to add a column with NOT NULL constrain, the table must be
empty.
20. Where the integrity constrints are stored in Data Dictionary ?
The integrity constraints are stored in USER_CONSTRAINTS.
21. How will you a activate/deactivate integrity constraints ?
The integrity constraints can be enabled or disabled by ALTER TABLE
ENABLE constraint/DISABLE constraint.
22. If an unique key constraint on DATE column is created, will it
validate the rows that are inserted with SYSDATE ?
It won't, Because SYSDATE format contains time attached with it.
23. What is a database link ?
Database Link is a named path through which a remote database
can be accessed.
24. How to access the current value and next value from a sequence ?
Is it possible to access the current value in a session before
accessing next value ?
Sequence name CURRVAL, Sequence name NEXTVAL.
It is not possible. Only if you access next value in the session,
current value can be accessed.
25. What is CYCLE/NO CYCLE in a Sequence ?
CYCLE specifies that the sequence continues to generate values
after reaching either maximum or minimum value. After pan
ascending sequence reaches its maximum value, it generates its
minimum value. After a descending sequence reaches its minimum, it
generates its maximum.
NO CYCLE specifies that the sequence cannot generate more values
after reaching its maximum or minimum value.
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