[OCPJP]ResultSet的用法

Given the records from the Employee table:

eid    ename
111    Tom
112    Jerry
113    Donald

and given the code fragment:

try {
    Connection conn = DriverManager.getConnection(URL, userName, passWord);
    Statement st = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE);
    st.execute("SELECT * FROM Employee");
    ResultSet rs = st.getResultSet();
    while (rs.next()) {
        if (rs.getInt(1) == 112) {
            rs.updateString(2, "Jack");
        }
    }
    rs.absolute(2);
    System.out.println(rs.getInt(1) + " " + rs.getString(2));
} catch (SQLException ex) {
    System.out.println("Exception is raised");
}

Assume that:

What is the result?

A.
The Employee table is updated with the row:
112 Jack
and the program prints:
112 Jerry
B.
The Employee table is updated with the row:
112 Jack
and the program prints:
112 Jack
C.
The Employee table is not updated and the program prints:
112 Jerry
D. The program prints Exception is raised.

題解

第22行建立Statement物件時所傳入的resultSetType為TYPE_SCROLL_INSENSITIVE，因此除了可以用next來移動欄位指標之外，也可以使用afterLast、previous、absolute和relative等方法。TYPE_SCROLL_SENSITIVE會使用後來更動的資料；TYPE_SCROLL_INSENSITIVE會保留資料庫中的原始資料，如果想要更動資料庫，需要在程式中將列修改之後，明確呼叫refreshRow方法。

while迴圈會執行三次，走訪完所有的結果列。在這個過程中，eid為112的列的第二個欄位，「Jerry」字串會被修改為「Jack」字串。但由於resultSetType為TYPE_SCROLL_INSENSITIVE，也沒有在修改後去呼叫refreshRow方法，所以這個修改不會被保留。