JDBC ResultSet Objects

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Questions and Answers

What is the initial position of the cursor in a ResultSet object?

  • Randomly positioned within the ResultSet
  • At the last row of data
  • At the first row of data
  • Before the first row of data (correct)

Which property of a default ResultSet object restricts how it can be iterated?

  • It can be updated with new data
  • It can only move forward through the rows (correct)
  • It can display changes made by others
  • It can only move backward through the rows

How can you retrieve data from a ResultSet more efficiently?

  • Using random access
  • Using a mix of column names and indices
  • Using column index numbers (correct)
  • Using column names only

What happens if a getter method is called with a column name that has duplicates in the ResultSet?

<p>The value of the first matching column is returned (B)</p> Signup and view all the answers

What is the purpose of the 'TYPE_SCROLL_INSENSITIVE' in the ResultSet creation?

<p>To ensure the ResultSet does not show changes made by others (C)</p> Signup and view all the answers

Why should result set columns within each row be read in left-to-right order?

<p>To ensure compatibility with all JDBC drivers (A)</p> Signup and view all the answers

What type of values does a JDBC driver return when using getter methods on a ResultSet?

<p>Java types specified in the getter method (A)</p> Signup and view all the answers

What is a key characteristic of an updatable ResultSet?

<p>It allows for modifications to the data (B)</p> Signup and view all the answers

What is the purpose of the SQL AS clause in the context of using column names?

<p>To ensure column names have unique references. (A)</p> Signup and view all the answers

How can an updater method be used in the context of a ResultSet?

<p>To update values in the current row. (B)</p> Signup and view all the answers

What functionality does an updatable ResultSet provide that enhances data manipulation?

<p>Provides a staging area for inserting rows. (A)</p> Signup and view all the answers

What happens to a ResultSet object when the Statement object associated with it is closed?

<p>The ResultSet is automatically closed. (B)</p> Signup and view all the answers

In the provided code fragment, which method is used to update the data source after changing a value in a ResultSet?

<p>updateRow() (D)</p> Signup and view all the answers

What is the primary role of ResultSetMetaData in relation to ResultSet objects?

<p>To provide information about the columns of a ResultSet. (A)</p> Signup and view all the answers

When updating a column in the current row, what is the first method called to position the cursor in the provided code example?

<p>absolute() (C)</p> Signup and view all the answers

When using an updatable ResultSet, which of the following is necessary before inserting a new row?

<p>The cursor should be moved to the insert row. (D)</p> Signup and view all the answers

What is the primary purpose of the ResultSet.moveToInsertRow method?

<p>To navigate to a special row for constructing a new row. (A)</p> Signup and view all the answers

After inserting a row with ResultSet.insertRow, what should you do next?

<p>Move the cursor to a row other than the insert row. (A)</p> Signup and view all the answers

Which method is called to update a column in the insert row before inserting it into the ResultSet?

<p>ResultSet.updateString (D)</p> Signup and view all the answers

What can happen if another part of your application uses the same ResultSet while the cursor is still pointing to the insert row?

<p>Unexpected results can occur in the ResultSet. (D)</p> Signup and view all the answers

What does ResultSet.CONCUR_UPDATABLE indicate?

<p>The ResultSet can be updated by calling insert or update methods. (C)</p> Signup and view all the answers

What is the default concurrency level for a ResultSet object?

<p>CONCUR_READ_ONLY (A)</p> Signup and view all the answers

Which method would you call to check if a specified ResultSet type is supported by the JDBC driver?

<p>DatabaseMetaData.supportsResultSetType (A)</p> Signup and view all the answers

Which of the following options can be specified when creating a ResultSet to allow cursor movement both forwards and backwards?

<p>TYPE_SCROLL_SENSITIVE (A)</p> Signup and view all the answers

What happens to ResultSet objects when the Connection.commit method is called?

<p>They are closed if they are non-holdable. (D)</p> Signup and view all the answers

When using getter methods with a string as an identifier, how are multiple columns with the same name handled?

<p>The first matching column's value is returned. (C)</p> Signup and view all the answers

Which method must be called after modifying a value in a ResultSet to persist changes to the underlying database?

<p>ResultSet.updateRow (B)</p> Signup and view all the answers

Which JDBC driver feature may not be supported by all databases regarding ResultSet handling?

<p>HOLD_CURSORS_OVER_COMMIT (A)</p> Signup and view all the answers

Which method is recommended to retrieve a VARCHAR column value from a ResultSet?

<p>getString (D)</p> Signup and view all the answers

What is a key characteristic of ResultSet objects' default scroll sensitivity?

<p>They can only be scrolled forward. (B)</p> Signup and view all the answers

When using case-insensitive column names with getter methods, what should be ensured?

<p>Column names must be unique in the query result. (C)</p> Signup and view all the answers

When a ResultSet is created and the cursor is positioned before the first row, which method is used to move the cursor to the first row?

<p>ResultSet.next (D)</p> Signup and view all the answers

In the context of ResultSet property holdability, what does HOLD_CURSORS_OVER_COMMIT allow?

<p>ResultSet objects to not close on commit. (A)</p> Signup and view all the answers

To increase the likelihood of portability across different JDBC drivers, what is recommended when retrieving columns from a ResultSet?

<p>Read columns in left-to-right order. (B)</p> Signup and view all the answers

What might be a limitation when using getString to retrieve numeric types from a ResultSet?

<p>It converts the numeric value back to string requiring additional conversion. (D)</p> Signup and view all the answers

Which of the following statements is true regarding the cursor in a ResultSet object?

<p>The cursor is a pointer that starts positioned before the first row. (A)</p> Signup and view all the answers

What distinguishes a TYPE_FORWARD_ONLY ResultSet from other ResultSet types?

<p>It is limited to moving the cursor only in a forward direction. (C)</p> Signup and view all the answers

What is the purpose of the ResultSet.next method?

<p>To advance the cursor to the next row and return its status. (D)</p> Signup and view all the answers

Which statement correctly describes the capabilities of the ResultSet interface?

<p>It includes methods for both retrieving and manipulating query results. (C)</p> Signup and view all the answers

Which type of ResultSet cannot reflect changes made to the underlying database after it has been created?

<p>TYPE_SCROLL_INSENSITIVE (D)</p> Signup and view all the answers

How is the sensitivity of a ResultSet defined?

<p>By the ResultSet type and how it handles data changes. (B)</p> Signup and view all the answers

What is a characteristic of a PreparedStatement in relation to a ResultSet?

<p>It can create ResultSet objects through execution of SQL queries. (C)</p> Signup and view all the answers

What happens if ResultSet.next returns false?

<p>There are no more rows available for processing in the ResultSet. (A)</p> Signup and view all the answers

What type of SQL statements can be included in the batch that utilizes the executeBatch method?

<p>INSERT, UPDATE, DELETE statements (A)</p> Signup and view all the answers

What behavior must be disabled before beginning a batch update to allow for correct error handling?

<p>Auto-commit mode (B)</p> Signup and view all the answers

What method is used to clear the list of commands associated with a Statement object?

<p>clearBatch (D)</p> Signup and view all the answers

If a batch contains a SELECT statement, what kind of exception is thrown?

<p>BatchUpdateException (C)</p> Signup and view all the answers

What does the Statement.executeBatch method return if all commands are executed successfully?

<p>An array of affected rows (A)</p> Signup and view all the answers

What will happen if the Connection.commit method is not called after a batch update?

<p>The updates will not be permanent. (A)</p> Signup and view all the answers

Which of the following correctly identifies a potential limitation when using ResultSet for updates?

<p>Not all JDBC drivers support inserting new rows with ResultSet. (D)</p> Signup and view all the answers

Which command is correctly associated with adding a new SQL command to the batch?

<p>addBatch (A)</p> Signup and view all the answers

What must be done to the Connection object to enable auto-commit mode after completing a batch update?

<p>Manually set auto-commit to true. (C)</p> Signup and view all the answers

What structure stores the update counts produced by successful commands in a batch?

<p>UpdateCount array (D)</p> Signup and view all the answers

How are SQL commands executed in relation to their order in the batch?

<p>In the order they were added to the batch. (A)</p> Signup and view all the answers

What kind of exception contains an array of update counts similar to what the executeBatch method yields?

<p>BatchUpdateException (A)</p> Signup and view all the answers

Which method is called on a ResultSet to begin inserting a new row?

<p>insertRow (C)</p> Signup and view all the answers

Flashcards

Updating a column value

Modifying a specific column's data in an existing row of a ResultSet.

Inserting new row

Adding a new row with values to a table from a ResultSet.

Scrollable ResultSet

Allows moving cursor backward and forward within the ResultSet.

Insert Row

ResultSet method for adding a new row.

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Update Row

ResultSet method for changing data in an existing row.

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ResultSetMetaData

Object containing column information like types, properties and more of a ResultSet.

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Column Uniqueness

Ensuring that column names refer to intended columns, verified with AS clause.

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Automatic ResultSet Closure

ResultSet automatically closes if Statement object is closed, re-executed or used for another result.

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ResultSet Object

An object in JDBC that holds the result of a database query, containing rows of data.

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Updatable ResultSet

A ResultSet that lets you modify data in the database.

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ResultSet Cursor

A pointer that keeps track of the current row in the ResultSet.

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ResultSet Iterating

Traversing the result to retrieve data row by row using the cursor.

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Column Access (by index)

Retrieving data using the column's position in the table (starting at 1).

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Column Access (by name)

Retrieving data using the name of the column.

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JDBC

Java Database Connectivity, a standard API for connecting Java applications to databases.

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Cursor

A pointer within a ResultSet that points to the current row of data.

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ResultSet.next()

A method that moves the cursor to the next row in the ResultSet, returning true if successful and false if there are no more rows.

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ResultSet Types

Different categories of ResultSets with varying functionalities and characteristics.

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TYPE_FORWARD_ONLY

The default ResultSet type, allowing traversal only in forward direction from the first row to the last row, without backward navigation.

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Concurrent Changes

The way a ResultSet reflects updates made to the underlying database while the ResultSet is active.

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moveToInsertRow()

A method that moves the ResultSet cursor to the insert row. This is necessary before you can start constructing a new row using update methods.

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beforeFirst()

Moves the ResultSet cursor to before the first row. This is essential after inserting a row using insertRow() to avoid potential issues if other parts of the application are using the same ResultSet.

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Batch Update

Executing multiple SQL statements as a single unit, often used for efficient data manipulation.

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Statement Object

Represents a SQL statement that can be executed against a database, holding a list of commands for a batch update.

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addBatch() method

Adds a SQL command to the list of commands associated with a Statement object, allowing for batch execution.

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executeBatch() method

Executes the entire list of commands associated with a Statement object as a single batch update.

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clearBatch() method

Removes all SQL commands from the list associated with a Statement object.

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Auto-Commit Mode

A database setting that determines whether each SQL statement is committed automatically after execution.

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Disable Auto-Commit

Turns off automatic 'commit' after each SQL statement, allowing for batch operations.

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Update Count

A value indicating the number of rows affected by a database operation, such as an INSERT or UPDATE.

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BatchUpdateException

Indicates an error during the execution of a batch update, often caused by unsuccessful statement execution or queries in the batch.

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Parameterized Batch Update

Using placeholders within SQL commands to provide values dynamically during execution, ideal for repetitive operations.

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ResultSet.TYPE_SCROLL_SENSITIVE

A ResultSet type that enables the cursor to move both forward and backward through the results of a query.

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ResultSet.CONCUR_UPDATABLE

A concurrency type for ResultSet objects that allows modifications to the data within the ResultSet, enabling rows to be updated or deleted.

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SQLFeatureNotSupportedException

An exception indicating that a requested feature is not supported by the JDBC driver or database.

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Insert Row (ResultSet)

Adding a new row into a table through a ResultSet object, providing values for each column.

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Connection.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE)

Creates a Statement object with a scrollable and updatable ResultSet, enabling modifications and flexible navigation through the query results.

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ResultSet Concurrency

Determines the level of update functionality allowed on a ResultSet. It can be 'CONCUR_READ_ONLY' (default) or 'CONCUR_UPDATABLE'.

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ResultSet Holdability

Defines how long a ResultSet remains valid, specifically after a commit. It can be 'HOLD_CURSORS_OVER_COMMIT' or 'CLOSE_CURSORS_AT_COMMIT'.

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What is the default ResultSet concurrency?

The default ResultSet concurrency is 'CONCUR_READ_ONLY'.

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What is the default ResultSet holdability?

The default ResultSet holdability varies depending on the database.

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How to retrieve column values from a ResultSet

Use methods like 'getBoolean', 'getInt', 'getString' with either column index (starting from 1) or column name.

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Why is column index access more efficient?

Directly referencing the position without searching for names is faster.

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What is the purpose of column aliases?

To provide unique and meaningful names to columns in the result set for easier access and understanding.

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How to create a scrollable ResultSet?

Use the 'TYPE_SCROLL_SENSITIVE' constant when creating the ResultSet object.

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What is the purpose of 'updateRow'?

It saves changes made to a ResultSet object back to the database.

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How do I update a column value in a ResultSet?

Use the appropriate 'update' method (e.g., 'updateFloat', 'updateString') followed by 'updateRow' to commit the changes.

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How to move the ResultSet cursor?

Use methods like 'next()', 'previous()', 'absolute()', 'relative()', or 'first()'.

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What is the difference between 'CONCUR_READ_ONLY' and 'CONCUR_UPDATABLE'?

CONCUR_READ_ONLY restricts to reading data while CONCUR_UPDATABLE enables modifications to the ResultSet.

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What are the advantages of using getters with column names?

It makes the code more readable and maintainable, especially when using aliases.

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What happens to ResultSet objects when the corresponding Statement object is closed?

ResultSet objects associated with a Statement object are also automatically closed.

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Study Notes

ResultSet Objects in JDBC

  • ResultSet objects store the results of database queries.
  • Initialized: Cursor positioned before the first row.
  • Iteration: next() method moves cursor to the next row. Returns false when no more rows exist, usable in a while loop.
  • Default: Non-updatable, forward-only cursor. Only iterates through the result once in a forward order.
  • Scrollable and Updatable: Create updatable result sets with a specific statement.
Statement stmt = con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE);
ResultSet rs = stmt.executeQuery("SELECT a, b FROM TABLE2");
  • This creates a scrollable ResultSet (not affected by changes from other sources) and updatable.
  • Retrieving Values: Getter methods (getBoolean, getLong, etc.) retrieve column values.
    • Use column index (starting at 1) or name. Column index is more efficient.
    • Read columns in left-to-right order and only once per column for best practice.
    • Column names are case-insensitive. Pick the first matching column.
    • Use column names when they're explicitly in the SQL query; use column numbers for unnamed columns.
  • JDBC Data Type Mapping: ResultSet getter methods translate SQL types to Java types. JDBC spec (table) describes allowed mappings.
  • Updater Methods (JDBC 2.0+):
  • Modify existing rows.
rs.absolute(5); // move cursor to the 5th row
rs.updateString("NAME", "AINSWORTH"); // update NAME to AINSWORTH
rs.updateRow();  // Update the database row
  • Add new rows:
rs.moveToInsertRow(); // Move to the special insert row
rs.updateString(1, "AINSWORTH"); // Set the first column in the insert row 
rs.updateInt(2,35);
rs.updateBoolean(3, true);
rs.insertRow();  //add to the database
rs.moveToCurrentRow();  // Go back to regular data rows
  • ResultSet Closure: Automatically closed when parent Statement closes, re-executed, or used for subsequent results in a sequence.
  • Metadata: ResultSet.getMetaData() returns ResultSetMetaData which gives information about the result set, like the number of columns and column types.

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