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:

1. Navigational methods: used to move the cursor around.

2. Get methods: used to view the data in the columns of the current row being pointed to by the cursor.

3. 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 generated the ResultSet is created.

JDBC provides following connection methods to create statements with desired ResultSet:

1. createStatement(int RSType, int RSConcurrency);

2. prepareStatement(String SQL, int RSType, int RSConcurrency);

3. prepareCall(String sql, int RSType, int RSConcurrency);

The first argument indicate 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.

Type of ResultSet:

The possible RSType are given below, If you do'nt specify any ResultSet type, you will automatically get one that is TYPE_FORWARD_ONLY.

Concurrency of ResultSet:

The possible RSConcurrency are given below, If you do'nt specify any Concurrency type, you will automatically get one that is CONCUR_READ_ONLY.

Our all the 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 {
   ....
}

Navigating a Result Set:

There are several methods in the ResultSet interface that involve moving the cursor, including:

For better understanding, Learn Navigate - Example Code.

Viewing a Result Set:

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:

1. One that takes in a column name.

2. 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:

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 better understanding, Learn Viewing - Example Code.

Updating a Result Set:

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:

1. One that takes in a column name.

2. 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:

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.

For better understanding, Learn Updating - Example Code.