JDBC - Learn Java by Examples

How do I limit MySQL query result?

By I Wayan Saryada in JDBC Last modified: May 31, 2024 0 Comment

package org.kodejava.jdbc;

import java.sql.DriverManager;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class SqlLimitExample {
    private static final String URL = "jdbc:mysql://localhost/kodejava";
    private static final String USERNAME = "kodejava";
    private static final String PASSWORD = "s3cr*t";

    public static void main(String[] args) {
        try (Connection connection =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {

            // Create PreparedStatement to get all data from a database.
            String query = "select count(*) from product";
            PreparedStatement ps = connection.prepareStatement(query);
            ResultSet result = ps.executeQuery();

            int total = 0;
            while (result.next()) {
                total = result.getInt(1);
            }

            System.out.println("Total number of data in database: " +
                               total + "\n");

            // Create PreparedStatement to the first 5 records only.
            query = "select * from product limit 5";
            ps = connection.prepareStatement(query);
            result = ps.executeQuery();

            System.out.println("Result fetched with specified limit 5");
            System.out.println("====================================");
            while (result.next()) {
                System.out.println("id:" + result.getInt("id") +
                                   ", code:" + result.getString("code") +
                                   ", name:" + result.getString("name") +
                                   ", price:" + result.getString("price"));
            }

            // Create PreparedStatement to get data from the 4th
            // record (remember the first record is 0) and limited
            // to 3 records only.
            query = "select * from product limit 3, 3";
            ps = connection.prepareStatement(query);
            result = ps.executeQuery();

            System.out.println("\nResult fetched with specified limit 3, 3");
            System.out.println("====================================");
            while (result.next()) {
                System.out.println("id:" + result.getInt("id") +
                                   ", code:" + result.getString("code") +
                                   ", name:" + result.getString("name") +
                                   ", price:" + result.getString("price"));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

An example result of our program is:

Total number of data in database: 9

Result fetched with specified limit 5
====================================
id:1, code:P0000001, name:UML Distilled 3rd Edition, price:25.00
id:3, code:P0000003, name:PHP Programming, price:20.00
id:4, code:P0000004, name:Longman Active Study Dictionary, price:40.00
id:5, code:P0000005, name:Ruby on Rails, price:24.00
id:6, code:P0000006, name:Championship Manager, price:0.00

Result fetched with specified limit 3, 3
====================================
id:5, code:P0000005, name:Ruby on Rails, price:24.00
id:6, code:P0000006, name:Championship Manager, price:0.00
id:7, code:P0000007, name:Transport Tycoon Deluxe, price:0.00

Maven Dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.4.0</version>
</dependency>

How do I set the fetch size of a statement?

By I Wayan Saryada in JDBC Last modified: May 31, 2024 0 Comment

Fetch size is the number of rows that should be fetched from the database on a single database network trip. When more rows are needed, another request is sent by the application to the database server.

Setting the correct fetch size will help our program to perform better by reducing the network communication generated between the program and the database server.

package org.kodejava.jdbc;

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

public class SetFetchSizeExample {
    private static final String URL = "jdbc:mysql://localhost/kodejava";
    private static final String USERNAME = "kodejava";
    private static final String PASSWORD = "s3cr*t";

    public static void main(String[] args) {
        try (Connection connection =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {
            Statement statement = connection.createStatement();

            // Set the fetch size to 100.
            statement.setFetchSize(100);

            // Execute the given sql query
            String q = "select id, code, name, price from product";
            ResultSet rs = statement.executeQuery(q);

            while (rs.next()) {
                System.out.println("id:" + rs.getLong("id") +
                                   ", code:" + rs.getString("code") +
                                   ", name:" + rs.getString("name") +
                                   ", price:" + rs.getString("price"));
            }

        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

Example result of the code snippet above is:

id:1, code:P0000001, name:UML Distilled 3rd Edition, price:25.00
id:3, code:P0000003, name:PHP Programming, price:20.00
id:4, code:P0000004, name:Longman Active Study Dictionary, price:40.00
id:5, code:P0000005, name:Ruby on Rails, price:24.00
id:6, code:P0000006, name:Championship Manager, price:0.00
id:7, code:P0000007, name:Transport Tycoon Deluxe, price:0.00
id:8, code:P0000008, name:Roller Coaster Tycoon 3, price:0.00
id:9, code:P0000009, name:Pro Evolution Soccer, price:0.00
id:10, code:P0000010, name:Data Structures, Algorithms, price:50.99

Maven Dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.4.0</version>
</dependency>

How do I set the maximum rows to read in a query?

By I Wayan Saryada in JDBC Last modified: May 31, 2024 0 Comment

If you want to limit the result of your query, you can call the Statement.setMaxRows(int max) method. This call will allow the ResultSet object contains a maximum number of records specified in the parameter of the setMaxRows method.

Another way to limit the number of data returned in a query is to use the database-specific command such as the MySQL limit command.

package org.kodejava.jdbc;

import java.sql.*;

public class SetMaxRowExample {
    private static final String URL = "jdbc:mysql://localhost/kodejava";
    private static final String USERNAME = "kodejava";
    private static final String PASSWORD = "s3cr*t";

    public static void main(String[] args) {
        try (Connection connection =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {
            Statement statement = connection.createStatement();

            // Executes an SQL query to get the total number of data
            // in product table.
            String query = "select count(*) from product";
            ResultSet rs = statement.executeQuery(query);

            while (rs.next()) {
                System.out.println("Total Products: " + rs.getInt(1));
            }

            // Set the maximum row of data that can be stored in the
            // ResultSet.
            statement.setMaxRows(5);

            // Executes an SQL query to retrieve data from product
            // table.
            query = "select id, code, name, price from product";
            rs = statement.executeQuery(query);

            System.out.println("Data read after the MaxRows is set.");
            while (rs.next()) {
                System.out.println("ID: " + rs.getInt("id")
                                   + ", CODE: " + rs.getString("code")
                                   + ", NAME: " + rs.getString("name")
                                   + ", PRICE: " + rs.getBigDecimal("price"));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

When running the code, we’ll see that only 5 records were read from the product table instead of 10 records. This is the result of setting the maximum rows in the Statement object.

Below is the output of our code.

Total Products: 9
Data read after the MaxRows is set.
ID: 1, CODE: P0000001, NAME: UML Distilled 3rd Edition, PRICE: 25.00
ID: 3, CODE: P0000003, NAME: PHP Programming, PRICE: 20.00
ID: 4, CODE: P0000004, NAME: Longman Active Study Dictionary, PRICE: 40.00
ID: 5, CODE: P0000005, NAME: Ruby on Rails, PRICE: 24.00
ID: 6, CODE: P0000006, NAME: Championship Manager, PRICE: 0.00

Maven Dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.4.0</version>
</dependency>

How do I convert java.util.Date to java.sql.Date?

By I Wayan Saryada in JDBC Last modified: July 31, 2023 0 Comment

package org.kodejava.jdbc;

import java.util.Date;

public class UtilDateToSqlDate {
    public static void main(String[] args) {
        // Create a new instance of java.util.Date
        Date date = new Date();

        // To covert java.util.Date to java.sql.Date we need to
        // create an instance of java.sql.Date and pass the long
        // value of java.util.Date as the parameter.
        java.sql.Date sqlDate = new java.sql.Date(date.getTime());

        System.out.println("Date    = " + date);
        System.out.println("SqlDate = " + sqlDate);
    }
}

The result of the code snippet above:

Date    = Sat Oct 09 20:23:27 CST 2021
SqlDate = 2021-10-09

How do I get system functions supported by database?

By I Wayan Saryada in JDBC Last modified: May 31, 2024 0 Comment

package org.kodejava.jdbc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.DatabaseMetaData;
import java.sql.SQLException;

public class SystemFunction {
    private static final String URL = "jdbc:mysql://localhost/kodejava";
    private static final String USERNAME = "kodejava";
    private static final String PASSWORD = "s3cr*t";

    public static void main(String[] args) {
        try (Connection connection =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {
            DatabaseMetaData meta = connection.getMetaData();

            // Get system functions supported by database
            String[] functions = meta.getSystemFunctions().split(",\\s*");

            for (String function : functions) {
                System.out.println("Function = " + function);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

Here are MySQL database supported system functions.

Function = DATABASE
Function = USER
Function = SYSTEM_USER
Function = SESSION_USER
Function = PASSWORD
Function = ENCRYPT
Function = LAST_INSERT_ID
Function = VERSION

Maven Dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.4.0</version>
</dependency>