Behavioral Data Access Interview Questions & Answers:

1. Explain What are the values that can be specified for OPTIMIZER MODE Parameter?

COST and RULE.

2. Explain What are the factors that affect OPTIMIZER in choosing an Optimization approach?

The OPTIMIZER_MODE initialization parameter Statistics in the Data Dictionary the OPTIMIZER_GOAL parameter of the ALTER SESSION command hints in the statement.

3. Explain What are the values that can be specified for OPTIMIZER_GOAL parameter of the ALTER SESSION Command?

CHOOSE,
ALL_ROWS,
FIRST_ROWS and
RULE.

4. What is COST-based approach to optimization?

Considering available access paths and determining the most efficient execution plan based on statistics in the data dictionary for the tables accessed by the statement and their associated clusters and indexes.

5. Explain What does ROLLBACK do?

ROLLBACK retracts any of the changes resulting from the SQL statements in the transaction.

6. Explain When does a Transaction end?

Commit, Rollback, DCL command like grant revoke.When exit from oracle (implicite commit happened), When database abnormally closed then an implicit rollback happened. When user invokes an DDl command

7. Explain There is a field of type character in the table, but we are storing numeric values like (Roll number) in this field, so if we want to sort the field (in java) according to numbers. How?

select to_number(rollnumber) from tname order by rollnumber

8. Explain What are the different approaches used by Optimizer in choosing an execution plan ?

Rule-based and Cost-based.

9. Explain What is the function of Optimizer?

The goal of the optimizer is to choose the most efficient way to execute a SQL statement.

10. Explain What does COMMIT do?

COMMIT makes permanent the changes resulting from all SQL statements in the transaction. The changes made by the SQL statements of a transaction become visible to other user sessions transactions that start only after transaction is committed.