[英]Correct way to find rowcount in Java JDBC
我尝试了不同的方法来获取 java JDBC 中的行数,但似乎没有一个给出正确的结果。 我做错了什么吗?
即使客户表是空的并且我应该将行数设为 0,但我不明白为什么我会得到一个非零行数值。
方法1 -
query = "SELECT * FROM customer WHERE username ='"+username+"'";
rs = stmt.executeQuery(query);
ResultSetMetaData metaData = rs.getMetaData();
rowcount = metaData.getColumnCount();
方法2 -
query = "SELECT * FROM customer WHERE username ='"+username+"'";
rs = stmt.executeQuery(query);
rowcount = rs.last() ? rs.getRow() : 0;
请看这段代码:
import java.io.*;
import java.sql.*;
public class CountRows{
public static void main(String[] args) {
System.out.println("Count number of rows in a specific table!");
Connection con = null;
int count = 0;
try {
Class.forName("com.mysql.jdbc.Driver");
con = DriverManager.getConnection("jdbc:mysql://localhost:3306/jdbctutorial","root","root");
try {
Statement st = con.createStatement();
BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
System.out.println("Enter table name:");
String table = bf.readLine();
ResultSet res = st.executeQuery("SELECT COUNT(*) FROM "+table);
while (res.next()){
count = res.getInt(1);
}
System.out.println("Number of row:"+count);
}
catch (SQLException s){
System.out.println("SQL statement is not executed!");
}
}
catch (Exception e){
e.printStackTrace();
}
}
}
这是我用来在 Java 中获取行数的方式:
String query = "SELECT * FROM yourtable";
Statement st = sql.createStatement( ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY );
ResultSet rs = st.executeQuery(query);
int rows = 0;
rs.last();
rows = rs.getRow();
rs.beforeFirst();
System.out.println("Your query have " + rows + " rows.");
当您使用不支持TYPE_FORWARD_ONLY
的 JDBC 时,请使用此方法获取行数。
Statement s = cd.createStatement();
ResultSet r = s.executeQuery("SELECT COUNT(*) AS rowcount FROM TableName");
r.next();
int count = r.getInt("rowcount");
r.close();
System.out.println("MyTable has " + count + " row(s).");
您可以使用上述方法获取行数。
谢谢..
在 Android 中,没有结果会返回错误。 因此,在while(resultset.next())中增加计数之前检查这种情况
if(resultset!=null)
{
//proceed with incrementing row count function
}
else
{
// No resultset found
}
只需迭代和计数
ResultSet result = sta.executeQuery("SELECT * from A3");
int k=0;
while(result.next())
k++;
System.out.print(k); //k is the no of row
由于方法名称指定metaData.getColumnCount()
将返回结果集中的总列数,但不返回总行数(计数)。
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