JDBC - Result Sets

The SQL statements that read data from a database query, return the data in a result set. The SELECT statement is the standard way to select rows from a database and view them in a result set. The java.sql.ResultSet interface represents the result set of a database query.
A ResultSet object maintains a cursor that points to the current row in the result set.  The term "result set" refers to the row and column data contained in a ResultSet object.
The methods of the ResultSet interface can be broken down into three categories −
Navigational methods − Used to move the cursor around.
Navigational methods − Used to move the cursor around.
Get methods − Used to view the data in the columns of the current row being pointed by the cursor.
Get methods − Used to view the data in the columns of the current row being pointed by the cursor.
Update methods − Used to update the data in the columns of the current row. The updates can then be updated in the underlying database as well.
Update methods − Used to update the data in the columns of the current row. The updates can then be updated in the underlying database as well.
The cursor is movable based on the properties of the ResultSet. These properties are designated when the corresponding Statement that generates the ResultSet is created.
JDBC provides the following connection methods to create statements with desired ResultSet −
createStatement(int RSType, int RSConcurrency);
createStatement(int RSType, int RSConcurrency);
prepareStatement(String SQL, int RSType, int RSConcurrency);
prepareStatement(String SQL, int RSType, int RSConcurrency);
prepareCall(String sql, int RSType, int RSConcurrency);
prepareCall(String sql, int RSType, int RSConcurrency);
The first argument indicates the type of a ResultSet object and the second argument is one of two ResultSet constants for specifying whether a result set is read-only or updatable.
The possible RSType are given below. If you do not specify any ResultSet type, you will automatically get one that is TYPE_FORWARD_ONLY.
The possible RSConcurrency are given below. If you do not specify any Concurrency type, you will automatically get one that is CONCUR_READ_ONLY.
All our examples written so far can be written as follows, which initializes a Statement object to create a forward-only, read only ResultSet object −
try {
   Statement stmt = conn.createStatement(ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY);
}
catch(Exception ex) {
   ....
}
finally {
   ....
}
There are several methods in the ResultSet interface that involve moving the cursor, including −
Moves the cursor just before the first row.
Moves the cursor just after the last row.
Moves the cursor to the first row.
Moves the cursor to the last row.
Moves the cursor to the specified row.
Moves the cursor the given number of rows forward or backward, from where it is currently
pointing.
Moves the cursor to the previous row. This method returns false if the previous row is off the
result set.
Moves the cursor to the next row. This method returns false if there are no more rows in the
result set.
Returns the row number that the cursor is pointing to.
 Moves the cursor to a special row in the result set that can be used to insert a new row
into the database. The current cursor location is remembered.
 Moves the cursor back to the current row if the cursor is currently at the insert row;
otherwise, this method does nothing
For a better understanding, let us study Navigate - Example Code.
The ResultSet interface contains dozens of methods for getting the data of the current row.
There is a get method for each of the possible data types, and each get method has two versions −
One that takes in a column name.
One that takes in a column name.
One that takes in a column index.
One that takes in a column index.
For example, if the column you are interested in viewing contains an int, you need to use one of the getInt() methods of ResultSet −
Returns the int in the current row in the column named columnName.
 Returns the int in the current row in the specified column index. The column index
starts at 1, meaning the first column of a row is 1, the second column of a row is 2, and so on.
Similarly, there are get methods in the ResultSet interface for each of the eight Java primitive types, as well as common types such as java.lang.String, java.lang.Object, and java.net.URL.
There are also methods for getting SQL data types java.sql.Date, java.sql.Time, java.sql.TimeStamp, java.sql.Clob, and java.sql.Blob. Check the documentation for more information about using these SQL data types.
For a better understanding, let us study Viewing - Example Code.
The ResultSet interface contains a collection of update methods for updating the data of a result set.
As with the get methods, there are two update methods for each data type −
One that takes in a column name.
One that takes in a column name.
One that takes in a column index.
One that takes in a column index.
For example, to update a String column of the current row of a result set, you would use one of the following updateString() methods −
Changes the String in the specified column to the value of s.
Similar to the previous method, except that the column is
specified by its name instead of its index.
There are update methods for the eight primitive data types, as well as String, Object, URL, and the SQL data types in the java.sql package.
Updating a row in the result set changes the columns of the current row in the ResultSet object, but not in the underlying database. To update your changes to the row in the database, you need to invoke one of the following methods.
Updates the current row by updating the corresponding row in the database.
Deletes the current row from the database
Refreshes the data in the result set to reflect any recent changes in the database.
Cancels any updates made on the current row.
Inserts a row into the database. This method can only be invoked when the cursor is pointing to the insert row.
For a better understanding, let us study the Updating - Example Code .

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