How to get row count using ResultSet in Java?

Question

I\'m trying to create a simple method that receives a ResultSet as a parameter and returns an int that contains the row count of the ResultSet. Is this a valid way of doing

Answer 1

If you have table and storing the ID as primary and auto increment then this will work

Example code to get the total row count http://www.java2s.com/Tutorial/Java/0340__Database/GettheNumberofRowsinaDatabaseTable.htm

Below is code

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.Statement;

public class Main {
  public static void main(String[] args) throws Exception {
    Connection conn = getConnection();
    Statement st = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
        ResultSet.CONCUR_UPDATABLE);

    st.executeUpdate("create table survey (id int,name varchar(30));");
    st.executeUpdate("insert into survey (id,name ) values (1,'nameValue')");
    st.executeUpdate("insert into survey (id,name ) values (2,null)");
    st.executeUpdate("insert into survey (id,name ) values (3,'Tom')");
    st = conn.createStatement();
    ResultSet rs = st.executeQuery("SELECT * FROM survey");

    rs = st.executeQuery("SELECT COUNT(*) FROM survey");
    // get the number of rows from the result set
    rs.next();
    int rowCount = rs.getInt(1);
    System.out.println(rowCount);

    rs.close();
    st.close();
    conn.close();

  }

  private static Connection getConnection() throws Exception {
    Class.forName("org.hsqldb.jdbcDriver");
    String url = "jdbc:hsqldb:mem:data/tutorial";

    return DriverManager.getConnection(url, "sa", "");
  }
}

Answer 2

your sql Statement creating code may be like

statement = connection.createStatement();

To solve "com.microsoft.sqlserver.jdbc.SQLServerException: The requested operation is not supported on forward only result sets" exception change above code with

statement = connection.createStatement(
    ResultSet.TYPE_SCROLL_INSENSITIVE, 
    ResultSet.CONCUR_READ_ONLY);

After above change you can use

int size = 0;
try {
    resultSet.last();
    size = resultSet.getRow();
    resultSet.beforeFirst();
}
catch(Exception ex) {
    return 0;
}
return size;

to get row count

Answer 3

The ResultSet has it's methods that move the Cursor back and forth depending on the option provided. By default, it's forward moving(TYPE_FORWARD_ONLY ResultSet type). Unless CONSTANTS indicating Scrollability and Update of ResultSet properly, you might end up getting an error. E.g. beforeLast() This method has no effect if the result set contains no rows. Throws Error if it's not TYPE_FORWARD_ONLY.

The best way to check if empty rows got fetched --- Just to insert new record after checking non-existence

if( rs.next() ) {

   Do nothing
} else {
  No records fetched!
}

See here

Answer 4

From http://docs.oracle.com/javase/1.4.2/docs/api/java/sql/ResultSetMetaData.html

 ResultSet rs = stmt.executeQuery("SELECT a, b, c FROM TABLE2");
 ResultSetMetaData rsmd = rs.getMetaData();
 int numberOfColumns = rsmd.getColumnCount();

A ResultSet contains metadata which gives the number of rows.

Answer 5

Others have already answered how to solve your problem, so I won't repeat what has already been said, but I will says this: you should probably figure out a way to solve your problems without knowing the result set count prior to reading through the results.

There are very few circumstances where the row count is actually needed prior to reading the result set, especially in a language like Java. The only case I think of where a row count would be necessary is when the row count is the only data you need(in which case a count query would be superior). Otherwise, you are better off using a wrapper object to represent your table data, and storing these objects in a dynamic container such as an ArrayList. Then, once the result set has been iterated over, you can get the array list count. For every solution that requires knowing the row count before reading the result set, you can probably think of a solution that does so without knowing the row count before reading without much effort. By thinking of solutions that bypass the need to know the row count before processing, you save the ResultSet the trouble of scrolling to the end of the result set, then back to the beginning (which can be a VERY expensive operation for large result sets).

Now of course I'm not saying there are never situations where you may need the row count before reading a result set. I'm just saying that in most circumstances, when people think they need the result set count prior to reading it, they probably don't, and it's worth taking 5 minutes to think about whether there is another way.

Just wanted to offer my 2 cents on the topic.

Answer 6

If you have access to the prepared statement that results in this resultset, you can use

connection.prepareStatement(sql, 
  ResultSet.TYPE_SCROLL_INSENSITIVE, 
  ResultSet.CONCUR_READ_ONLY);

This prepares your statement in a way that you can rewind the cursor. This is also documented in the ResultSet Javadoc

In general, however, forwarding and rewinding cursors may be quite inefficient for large result sets. Another option in SQL Server would be to calculate the total number of rows directly in your SQL statement:

SELECT my_table.*, count(*) over () total_rows
FROM my_table
WHERE ...