Data retrieval in JDBC applications
In JDBC applications, you retrieve data using ResultSet objects. A ResultSet
represents the result set of a query.
Retrieving data from tables using the Statement.executeQuery
method
To retrieve data from a table using a SELECT statement with no parameter
markers, you can use the Statement.executeQuery method.
This method returns a result table in a ResultSet object. After you obtain the result
table, you need to use ResultSet methods to move through the result table and
obtain the individual column values from each row.
With the IBM Data Server Driver for JDBC and SQLJ, you can also use the
Statement.executeQuery method to retrieve a result set from a stored procedure
call, if that stored procedure returns only one result set. If the stored procedure
returns multiple result sets, you need to use the Statement.execute method.
This topic discusses the simplest kind of ResultSet, which is a read-only ResultSet
in which you can only move forward, one row at a time. The IBM Data Server
Driver for JDBC and SQLJ also supports updatable and scrollable ResultSets.
To retrieve rows from a table using a SELECT statement with no parameter
markers, you need to perform these steps:
1. Invoke the Connection.createStatement method to create a Statement object.
2. Invoke the Statement.executeQuery method to obtain the result table from the
SELECT statement in a ResultSet object.
3. In a loop, position the cursor using the next method, and retrieve data from
each column of the current row of the ResultSet object using getXXX methods.
XXX represents a data type.
4. Invoke the ResultSet.close method to close the ResultSet object.
5. Invoke the Statement.close method to close the Statement object when you
have finished using that object.
The following code demonstrates how to retrieve all rows from the employee table.
The numbers to the right of selected statements correspond to the
previously-described steps.
Related concepts
String empNo;
Connection con;
Statement stmt;
ResultSet rs;
...
stmt = con.createStatement(); // Create a Statement object 1
rs = stmt.executeQuery("SELECT EMPNO FROM EMPLOYEE"); 2
// Get the result table from the query
while (rs.next()) { // Position the cursor 3
empNo = rs.getString(1); // Retrieve only the first column value
System.out.println("Employee number="+empNo);
// Print the column value
}
rs.close(); // Close the ResultSet 4
stmt.close(); // Close the Statement 5
Figure 12. Using Statement.executeQuery
32 Application Programming Guide and Reference for Java
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