Oracle Data Access

Use this SQL query :delete from student_tab A where ROWID > ( select min(ROWID) from student_tab B where A.roll_number = B.roll_number);Note : Table Name = student_tab Key to table = roll_number

Yes ,, we can delete entries from a table based on the date column,,Only we have to mention the date format or other wise we'll have to make use of the sys date.

This value causes the optimizer to the cost-based approach for all SQL statements in the session regardless of the presence of statistics and to optimize with a goal of best throughput.

A Read-Only transaction ensures that the results of each query executed in the transaction are consistant with respect to the same point in time.

The combination of the steps the optimizer chooses to execute a statement is called an execution plan.

For long transactions that contain many SQL statements, intermediate markers or savepoints can be declared which can be used to divide a transaction into smaller parts. This allows the option of later rolling back all work performed from the current point in the transaction to a declared savepoint within the transaction.

The Optimizer chooses Cost_based approach and optimizes with the goal of best throughput if statistics for atleast one of the tables accessed by the SQL statement exist in the data dictionary. Otherwise the OPTIMIZER chooses RULE_based approach.

Choosing an executing planbased on the access paths available and the ranks of these access paths.

A Transaction is a logical unit of work that comprises one or more SQL statements executed by a single user.

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.

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

Rule-based and Cost-based.

select to_number(rollnumber) from tname order by rollnumber

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

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

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.

CHOOSE,

ALL_ROWS,

FIRST_ROWS and

RULE.

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

COST and RULE.