Wipro DBMS Sample Interview Questions

Question 1
(In DBMS like Oracle) Which of the following allow null values ? A Unique Key or Primary Key ?
Answer :
Primary Key constraint does not allow null values to be inserted while it is legal in case of Unique key.
Question 2
Considering an Oracle database as an example, can NULL values be used in arithmetic operations ? Explain your answer ?
Answer :
No, NULL value cannot be used in arithmetic operation. This is because a NULL just denotes an 'absence' of information rather than 'empty' or 'zero' value.
Question 3
How you can delete a duplicate row from Unique key column?
Answer :
This necessity does not arise. First of all Unique key column will not allow duplicate rows to be inserted.
Question 4
Tell any one advantage of using stored procedures in applications?
Answer :
Stored Procedures abstract complex SQL queries from application code. For example, a task involving multiple lines of complex SQL queries can be simplified to a single stored procedure call.

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