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Java sql select parameter

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Содержание
  1. Java JDBC CRUD Tutorial: SQL Insert, Select, Update, and Delete Examples
  2. 1. Prerequisites
  3. 2. Creating a sample MySQL database
  4. 3. Understand the main JDBC interfaces and classes
  5. 4. Connecting to the database
  6. 5. JDBC Execute INSERT Statement Example
  7. 6. JDBC Execute SELECT Statement Example
  8. 7. JDBC Executing UPDATE Statement Example
  9. 8. JDBC Execute DELETE Statement Example
  10. JDBC API References:
  11. Related JDBC Tutorials:
  12. About the Author:

Java JDBC CRUD Tutorial: SQL Insert, Select, Update, and Delete Examples

This JDBC tutorial is going to help you learning how to do basic database operations (CRUD — Create, Retrieve, Update and Delete) using JDBC (Java Database Connectivity) API. These CRUD operations are equivalent to the INSERT, SELECT, UPDATE and DELETE statements in SQL language. Although the target database system is MySQL, but the same technique can be applied for other database systems as well because the query syntax used is standard SQL which is supported by all relational database systems.

We will learn how to do insert, query, update and delete database records by writing code to manage records of a table Users in a MySQL database called SampleDB.

Table of content:

1. Prerequisites

    • JDK (download JDK 7).
    • MySQL (download MySQL Community Server 5.6.12). You may also want to download MySQL Workbench — a graphical tool for working with MySQL databases.
    • JDBC Driver for MySQL (download MySQL Connector/J 5.1.25). Extract the zip archive and put the mysql-connector-java-VERSION-bin.jar file into classpath (in a same folder as your Java source files).

    2. Creating a sample MySQL database

    Let’s create a MySQL database called SampleDB with one table Users with the following structure:

    Users table structures

    Execute the following SQL script inside MySQL Workbench:

    create database SampleDB; use SampleDB; CREATE TABLE `users` ( `user_id` int(11) NOT NULL AUTO_INCREMENT, `username` varchar(45) NOT NULL, `password` varchar(45) NOT NULL, `fullname` varchar(45) NOT NULL, `email` varchar(45) NOT NULL, PRIMARY KEY (`user_id`) );

    Or if you are using MySQL Command Line Client program, save the above script into a file, let’s say, SQLScript.sql and execute the following command:

    source Path\To\The\Script\File\SQLScript.sql

    Here’s an example screenshot taken while executing the above script in MySQL Command Line Client program:

    execute SQL script

    3. Understand the main JDBC interfaces and classes

    Let’s take an overview look at the JDBC’s main interfaces and classes with which we usually work. They are all available under the java.sql package:

      • DriverManager : this class is used to register driver for a specific database type (e.g. MySQL in this tutorial) and to establish a database connection with the server via its getConnection() method.
      • Connection : this interface represents an established database connection (session) from which we can create statements to execute queries and retrieve results, get metadata about the database, close connection, etc.
      • Statement and PreparedStatement : these interfaces are used to execute static SQL query and parameterized SQL query, respectively. Statement is the super interface of the PreparedStatement interface. Their commonly used methods are:
          • boolean execute(String sql) : executes a general SQL statement. It returns true if the query returns a ResultSet , false if the query returns an update count or returns nothing. This method can be used with a Statement only.
          • int executeUpdate(String sql) : executes an INSERT, UPDATE or DELETE statement and returns an update account indicating number of rows affected (e.g. 1 row inserted, or 2 rows updated, or 0 rows affected).
          • ResultSet executeQuery(String sql) : executes a SELECT statement and returns a ResultSet object which contains results returned by the query.

      A prepared statement is one that contains placeholders (in form question marks ?) for dynamic values will be set at runtime. For example:

      SELECT * from Users WHERE user_id=?

      Here the value of user_id is parameterized by a question mark and will be set by one of the setXXX() methods from the PreparedStatement interface, e.g. setInt(int index, int value) .

        • ResultSet : contains table data returned by a SELECT query. Use this object to iterate over rows in the result set using next() method, and get value of a column in the current row using getXXX() methods (e.g. getString() , getInt() , getFloat() and so on). The column value can be retrieved either by index number (1-based) or by column name.
        • SQLException : this checked exception is declared to be thrown by all the above methods, so we have to catch this exception explicitly when calling the above classes’ methods.

        4. Connecting to the database

        Supposing the MySQL database server is listening on the default port 3306 at localhost. The following code snippet connects to the database name SampleDB by the user root and password secret:

        String dbURL = «jdbc:mysql://localhost:3306/sampledb»; String username = «root»; String password = «secret»; try < Connection conn = DriverManager.getConnection(dbURL, username, password); if (conn != null) < System.out.println("Connected"); >> catch (SQLException ex)

        Once the connection was established, we have a Connection object which can be used to create statements in order to execute SQL queries. In the above code, we have to close the connection explicitly after finish working with the database:

        However, since Java 7, we can take advantage of the try -with-resources statement which will close the connection automatically, as shown in the following code snippet:

        try (Connection conn = DriverManager.getConnection(dbURL, username, password)) < // code to execute SQL queries goes here. >catch (SQLException ex)

        If you are using Java 7 or later, this approach is recommended. The sample programs in this tutorial are all using this try-with-resources statement to make a database connection.

        NOTE: For details about connecting to a MySQL database, see the article: Connect to MySQL database via JDBC.

        5. JDBC Execute INSERT Statement Example

          • username: bill
          • password: secretpass
          • fullname: Bill Gates
          • email: bill.gates@microsoft.com

          String sql = «INSERT INTO Users (username, password, fullname, email) VALUES (?, ?, ?, ?)»; PreparedStatement statement = conn.prepareStatement(sql); statement.setString(1, «bill»); statement.setString(2, «secretpass»); statement.setString(3, «Bill Gates»); statement.setString(4, «bill.gates@microsoft.com»); int rowsInserted = statement.executeUpdate(); if (rowsInserted > 0)

          In this code, we create a parameterized SQL INSERT statement and create a PreparedStatement from the Connection object. To set values for the parameters in the INSERT statement, we use the PreparedStatement ‘s setString() methods because all these columns in the table Users are of type VARCHAR which is translated to String type in Java. Note that the parameter index is 1-based (unlike 0-based index in Java array).

          The PreparedStatement interface provides various setXXX() methods corresponding to each data type, for example:

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