DATABASE & SQL/PLSQL

Oacle interview Questions And Answer
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Where the integrity constraints are stored in data dictionary?

The integrity constraints are stored in USER_CONSTRAINTS.

How will you activate/deactivate integrity constraints?

The integrity constraints can be enabled or disabled by ALTER TABLE ENABLE CONSTRAINT / DISABLE CONSTRAINT.

If 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.

What is a database link?

Database link is a named path through which a remote database can be accessed.

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.

What is CYCLE/NO CYCLE in a Sequence?

CYCLE specifies that the sequence continue 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.

What are the advantages of VIEW?

  • To protect some of the columns of a table from other users.
  • To hide complexity of a query.
  • To hide complexity of calculations.

Can a view be updated/inserted/deleted? If Yes - under what conditions?

A View can be updated/deleted/inserted if it has only one base table if the view is based on columns from one or more tables then insert, update and delete is not possible.

If a view on a single base table is manipulated will the changes be reflected on the base table?

If changes are made to the tables and these tables are the base tables of a view, then the changes will be reference on the view.

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