Tag: programming languages

To understand the meaning of the transaction isolation level TRANSACTION_REPEATABLE_READ, we need to know about transaction isolation levels in database management systems.

Transaction isolation level is a concept that ensures the correctness and consistency of database transactions. It defines the level of isolation between concurrent transactions in the system.

The TRANSACTION_REPEATABLE_READ isolation level guarantees that during the transaction, any row that is read will be locked for the duration of the transaction. This means that if the transaction tries to read the same row again, it will get the same value as before. This ensures that the transaction sees a consistent snapshot of the data.

Now let's go through each option to see which one is correct:

A. (a) Dirty reads, non-repeatable reads, and phantom reads can occur - This option is incorrect. The TRANSACTION_REPEATABLE_READ level prevents dirty reads and non-repeatable reads, but phantom reads can still occur.

B. (b) Dirty reads are prevented; non-repeatable reads and phantom reads can occur - This option is incorrect. The TRANSACTION_REPEATABLE_READ level prevents dirty reads, but non-repeatable reads and phantom reads can still occur.

C. (c) Dirty reads and non-repeatable reads are prevented; phantom reads can occur - This option is correct. The TRANSACTION_REPEATABLE_READ level prevents dirty reads and non-repeatable reads, but phantom reads can still occur.

D. (d) Dirty reads, non-repeatable reads, and phantom reads are prevented - This option is incorrect. The TRANSACTION_REPEATABLE_READ level only prevents dirty reads and non-repeatable reads, but phantom reads can still occur.

Therefore, the answer is: C. (c) Dirty reads and non-repeatable reads are prevented; phantom reads can occur.

The correct answer is A. You can execute a stored procedure in the database by calling the execute() method on a CallableStatement object.

Explanation:

A stored procedure is a precompiled set of SQL statements that are stored in the database. To execute a stored procedure, you need to create a CallableStatement object, which allows you to call the stored procedure.

Here's an example of how to execute a stored procedure using Java and JDBC:

// Assuming you have already established a database connection
CallableStatement cstmt = conn.prepareCall("{call your_stored_procedure(?, ?)}");

// Set any input parameters for the stored procedure, if needed
cstmt.setString(1, "input_parameter1");
cstmt.setInt(2, 2);

// Execute the stored procedure
cstmt.execute();

In the code above, your_stored_procedure is the name of the stored procedure you want to execute. The ? placeholders are used for any input parameters the stored procedure may require. You can set the input parameters using the setXxx() methods on the CallableStatement object.

Lastly, you call the execute() method on the CallableStatement object to execute the stored procedure.

To answer this question, the user needs to have a basic understanding of Java Database Connectivity (JDBC) and ResultSet objects.

Option A is incorrect. The close() method does exist for ResultSet objects.

Option B is correct. If you call the close() method on a ResultSet object, the resources associated with the ResultSet will be released and returned to the database. This includes any database and JDBC resources that were used to create the ResultSet.

Option C is incorrect. The close() method can be called on a ResultSet object, but not on a Statement object. It is the Statement object that creates the ResultSet.

Option D is incorrect. While the ResultSet is associated with the Statement and Connection objects that created it, calling the close() method on the ResultSet will only release the resources associated with the ResultSet itself, not the Statement or Connection objects.

Therefore, the answer is: B. O (b) the database and JDBC resources are released.

The correct answer to the question is B. The row you are positioned on is deleted from the ResultSet and from the database.

The deleteRow() method of the ResultSet interface deletes the current row from the ResultSet object and from the underlying database table. This means that the row will no longer be visible in the ResultSet object, and it will also be deleted from the database.

The deleteRow() method only works if the ResultSet object is updatable. An updatable ResultSet object is one that can be used to modify data in the database. To create an updatable ResultSet object, you must set the CONCUR_UPDATABLE property of the Statement object that you use to execute the query.

The deleteRow() method does not throw any exceptions. If you try to delete a row from a ResultSet object that is not updatable, the method will simply do nothing.

Here is an example of how to use the deleteRow() method:

import java.sql.*;

public class DeleteRowExample {

    public static void main(String[] args) throws SQLException {
        Connection connection = DriverManager.getConnection("jdbc:mysql://localhost/mydatabase", "username", "password");
        Statement statement = connection.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE);
        String sql = "SELECT * FROM customers";
        ResultSet resultSet = statement.executeQuery(sql);

        // Move the cursor to the first row.
        resultSet.first();

        // Delete the current row.
        resultSet.deleteRow();

        // Close the connection.
        connection.close();
    }
}

This code will delete the first row in the customers table.

To answer this question, the user needs to have knowledge about DDL (Data Definition Language) statements and their characteristics.

Now, let's go through each option and explain why it is right or wrong:

A. O (a) DDL statements are treated as normal SQL statements, and are executed by calling them. This statement is correct. DDL statements are used to define or modify the structure of database objects like tables, indexes, etc. and they are executed like normal SQL statements.

B. O (b) To execute DDL statements, you have to install additional support files. This statement is incorrect. There is no requirement for additional support files to execute DDL statements.

C. O (c) DDL statements cannot be executed by making use of JDBC, you should use the native database SQL interface. This statement is incorrect. DDL statements can be executed using JDBC (Java Database Connectivity) API like any other SQL statement.

D. O (d) Support for DDL statements will be a feature of a future release of JDBC. This statement is incorrect. DDL statements are already supported by JDBC.

Therefore, the correct option is:

The Answer is: A