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法學Java ResultSet previous() 方法及示例
當我們執行某些 SQL 查詢（通常是 SELECT 查詢）時，它們會返回表格資料。
java.sql.ResultSet 介面表示 SQL 語句返回的此類表格資料。
即，ResultSet 物件儲存由執行查詢資料庫的語句的方法（通常是 Statement 介面的 executeQuery() 方法）返回的表格資料。
ResultSet 物件有一個遊標/指標，它指向當前行。最初，此遊標位於第一行之前。
previous() 方法是 ResultSet 介面的方法，它將當前 (ResultSet) 物件的指標從當前位置移動到前一行。
此方法返回一個布林值，指定 ResultSet 物件是否包含更多行。如果在其當前位置之前沒有行，則此方法返回 false，否則返回 true。
注意：在 while 迴圈中使用此方法，您可以從後到前迭代 ResultSet 物件的內容。
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery("Select * from MyPlayers");
rs.afterLast();
rs.previous();即，如果遊標位於倒數第二行的下一位置，並且表包含 8 行，則第一次呼叫 previous() 方法時，結果集指標/遊標將移動到第 8 行（從倒數第二位置）。
第二次呼叫 previous() 方法時，結果集遊標將移動到第 7 行。
rs.afterLast();
while(rs.previous()) {
System.out.println(rs.getString(1));
System.out.println(rs.getString(2));
}示例
讓我們使用 CREATE 語句在 MySQL 資料庫中建立一個名為 MyPlayers 的表，如下所示：
CREATE TABLE MyPlayers( ID INT, First_Name VARCHAR(255), Last_Name VARCHAR(255), Date_Of_Birth date, Place_Of_Birth VARCHAR(255), Country VARCHAR(255), PRIMARY KEY (ID) );
現在，我們將使用 INSERT 語句在 MyPlayers 表中插入 7 條記錄：
insert into MyPlayers values(1, 'Shikhar', 'Dhawan', DATE('1981-12-05'), 'Delhi', 'India');
insert into MyPlayers values(2, 'Jonathan', 'Trott', DATE('1981-04-22'), 'CapeTown', 'SouthAfrica');
insert into MyPlayers values(3, 'Kumara', 'Sangakkara', DATE('1977-10-27'), 'Matale', 'Srilanka');
insert into MyPlayers values(4, 'Virat', 'Kohli', DATE('1988-11-05'), 'Delhi', 'India');
insert into MyPlayers values(5, 'Rohit', 'Sharma', DATE('1987-04-30'), 'Nagpur', 'India');
insert into MyPlayers values(6, 'Ravindra', 'Jadeja', DATE('1988-12-06'), 'Nagpur', 'India');
insert into MyPlayers values(7, 'James', 'Anderson', DATE('1982-06-30'), 'Burnley', 'England');下面的 JDBC 程式建立與資料庫的連線，將 MyPlayers 表的內容檢索到 ResultSet 物件中，使用 previous() 方法將遊標向前移動三次，從 ResultSet 物件的倒數第二位置開始，並列印每一位置行的內容。
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class ResultSet_previous {
public static void main(String args[]) throws SQLException {
//Registering the Driver
DriverManager.registerDriver(new com.mysql.jdbc.Driver());
//Getting the connection
String mysqlUrl = "jdbc:mysql:///mydatabase";
Connection con = DriverManager.getConnection(mysqlUrl, "root", "password");
System.out.println("Connection established......");
//Creating the Statement
Statement stmt = con.createStatement(
ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_UPDATABLE);
//Query to retrieve records
String query = "Select * from MyPlayers";
//Executing the query
ResultSet rs = stmt.executeQuery(query);
System.out.println("Contents of the last record: ");
//Moving the cursor position next to the last row
rs.afterLast();
//Moving the cursor from next to last position to the last (7th) row
rs.previous();
//Current record details.
System.out.print("ID: "+rs.getInt("ID")+", ");
System.out.print("Name: "+rs.getString("First_Name")+", ");
System.out.print("Age: "+rs.getString("Last_Name")+", ");
System.out.print("Salary: "+rs.getDate("Date_Of_Birth")+", ");
System.out.print("Country: "+rs.getString("Place_Of_Birth")+", ");
System.out.print("Address: "+rs.getString("Country"));
System.out.println();
//Moving the cursor from 7th row to 6th row.
rs.previous();
//Current record details.
System.out.print("ID: "+rs.getInt("ID")+", ");
System.out.print("Name: "+rs.getString("First_Name")+", ");
System.out.print("Age: "+rs.getString("Last_Name")+", ");
System.out.print("Salary: "+rs.getDate("Date_Of_Birth")+", ");
System.out.print("Country: "+rs.getString("Place_Of_Birth")+", ");
System.out.print("Address: "+rs.getString("Country"));
System.out.println();
//Moving the cursor from 6th row to 5th row.
rs.previous();
//Current record details.
System.out.print("ID: "+rs.getInt("ID")+", ");
System.out.print("Name: "+rs.getString("First_Name")+", ");
System.out.print("Age: "+rs.getString("Last_Name")+", ");
System.out.print("Salary: "+rs.getDate("Date_Of_Birth")+", ");
System.out.print("Country: "+rs.getString("Place_Of_Birth")+", ");
System.out.print("Address: "+rs.getString("Country"));
System.out.println();
//Moving the cursor from 5th row to 4th row.
rs.previous();
//Current record details.
System.out.print("ID: "+rs.getInt("ID")+", ");
System.out.print("Name: "+rs.getString("First_Name")+", ");
System.out.print("Age: "+rs.getString("Last_Name")+", ");
System.out.print("Salary: "+rs.getDate("Date_Of_Birth")+", ");
System.out.print("Country: "+rs.getString("Place_Of_Birth")+", ");
System.out.print("Address: "+rs.getString("Country"));
System.out.println();
}
}輸出
Connection established...... Contents of the last record: ID: 8, Name: Ryan, Age: McLaren, Salary: 1983-02-09, Country: Kumberly, Address: null ID: 7, Name: James, Age: Anderson, Salary: 1982-06-30, Country: Burnley , Address: England ID: 6, Name: Ravindra, Age: Jadeja, Salary: 1988-12-06, Country: Nagpur, Address: India ID: 5, Name: Rohit, Age: Sharma, Salary: 1987-04-30, Country: Nagpur, Address: India
更新於：2019年7月30日
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