我正在我的 java class 中处理数据库，我需要帮助弄清楚如何更新数据库中的特定值/列

Question

Here is my first class. This is where im building my table and plugging in some values. In the second class, I am only displaying firstName , lastName , and salary BUT I also need to display the salary once more, but this time adding an increase of 10%, or salary += salary*.1 to be clear

public class CreateEmployeeDB 
{

    public static void main(String[] args) 
    {
        final String DB_URL = "jdbc:derby:EmployeeDB;create=true";
        
        try
        {
            Connection conn =
                    DriverManager.getConnection(DB_URL);
                         
            dropTables(conn);
            buildEmployees(conn);
                
            conn.close();
        }
        
        catch (Exception ex)
        {
            System.out.println("ERROR: " + ex.getMessage());
        }
    }
    

    public static void dropTables(Connection conn)
    {
        
        try
        {
            // Get a Statement object.
            Statement stmt  = conn.createStatement();
            
            try
            {
                stmt.execute("DROP TABLE Employees");
            }
            catch(SQLException ex)
            {
                // No need to report an error.
                // The table simply did not exist.
            }
        }
        catch(SQLException ex)
        {
            System.out.println("ERROR: " + ex.getMessage());
            ex.printStackTrace();
        }
    }
            
    
    
    public static void buildEmployees(Connection conn)
    {
        try
        {
            Statement stmt = conn.createStatement();
            
            stmt.execute("CREATE TABLE Employees (" +
                    "socialSecurityNumber VARCHAR(30) NOT NULL PRIMARY KEY, " +
                    "firstName VARCHAR(30), " +
                    "lastName VARCHAR(30), " +
                    "weeklySalary DOUBLE, " +
                    "birthday DATE, " +
                    "employeeType VARCHAR(30), " +
                    "departmentName VARCHAR(30) " +
                    ")");
            
            
            stmt.execute("INSERT INTO EMPLOYEES VALUES( " +
                    "'11-1111', " +
                    "'John', " +
                    "'Smith', " +
                    "1000.50, " +
                    "'1945-01-02', " +
                    "'salariedEmployee', " +
                    "'R&D')");

            stmt.execute("INSERT INTO EMPLOYEES VALUES( " +
                    "'22-2222', " +
                    "'Sue', " +
                    "'Jones', " +
                    "865.00, " +
                    "'1961-02-03', " +
                    "'commissionEmployee', " +
                    "'SALES')");
            
            stmt.execute("INSERT INTO EMPLOYEES VALUES( " +
                    "'33-3333', " +
                    "'Bob', " +
                    "'Lowis', " +
                    "950.25, " +
                    "'1958-10-05', " +
                    "'basePlusEmployee', " +
                    "'SALES')");
            
            stmt.execute("INSERT INTO EMPLOYEES VALUES( " +
                    "'44-4444', " +
                    "'Karen', " +
                    "'Price', " +
                    "1100.15, " +
                    "'1972-05-25', " +
                    "'salariedEmployee', " +
                    "'HR')");
            
        }
            catch (SQLException ex)
        {
            System.out.println("ERROR: " + ex.getMessage());
        }

    }

}

here is my second class. How do I update the salary in here? I'm assuming I need to do something with SELECT ? But I can't quite figure it out.

public class UpdateSalary
{
        public static void main(String[] args) 
        {
            final String DB_URL = "jdbc:derby:EmployeeDB";
    
            try
            {
                Connection conn = DriverManager.getConnection(DB_URL);
                
                showSalary(conn);
                
                updateSalary(conn);
                
            
            }
            catch(Exception ex)
            {
                System.out.println("ERROR: " + ex.getMessage());
            }
    
        }
        
        public static void showSalary(Connection conn)
        {
            final String DB_URL = "jdbc:derby:Personnel";
            
            try
            {
    
                Statement stmt = conn.createStatement();
                
                String sqlStatement = "SELECT * FROM Employees";
    
                ResultSet result = stmt.executeQuery(sqlStatement);
                
                System.out.println("\n\t\t\t\t Employees Report - Current Salary ");
                System.out.println("-------------------------------");
                System.out.println("\t\t\t   First \t\t\tLast  Salary");
    
                while (result.next())
                {
                    System.out.printf("%30s %30s $%5.2f\n",
                            
                            result.getString("firstName"),
                            result.getString("lastName"),
                            result.getDouble("weeklySalary")
                            );
                }
                
                //conn.close();
            
            }
                catch(Exception ex)
                {
                    System.out.println("ERROR: " + ex.getMessage());
                }
        }
        
        public static void updateSalary(Connection conn)
        {
            final String DB_URL = "jdbc:derby:Personnel";
            
            try
            {
    
                Statement stmt = conn.createStatement();
                
                String sqlStatement = "SELECT weeklySalary FROM Employees  ";
    
                ResultSet result = stmt.executeQuery(sqlStatement);
                
                System.out.println("\n\t\t\t\t Employees Report - Updated Salary ");
                System.out.println("----------------------------------");
                System.out.println("\t\t\t   First \t\t\tLast  Salary");
    
                while (result.next())
                {
                    System.out.printf("%30s %30s $%5.2f\n",
                            
                            result.getString("firstName"),
                            result.getString("lastName"),
                            result.getDouble("weeklySalary")
                            );
                }
                
                conn.close();
            
            }
                catch(Exception ex)
                {
                    System.out.println("ERROR: " + ex.getMessage());
                }
        }
    
    }

i apologize for the messy code and weird formatting that you get in the output. If anyone has tips, I would appreciate it. Thank you for your time.

Answer 1

You can SELECT it by making the relevant changes and display the result directly. Although this does not affect the database's weeklySalary values.

SELECT firstName,lastName,weeklySalary*1.1 as weeklySalary FROM Employees 

You can create a SQL statement using UPDATE with the updated salary value and then execute the SQL statement using executeUpdate() . This will update the Database's weeklySalary values. Then, simply display the result.

Under updateSalary(Connection conn) replace in accordance.

        String updateSqlStatement = "UPDATE Employees SET weeklySalary = weeklySalary*1.1";
        stmt.executeUpdate(updateSqlStatement);
        String sqlStatement = "SELECT * FROM Employees";
        ResultSet result = stmt.executeQuery(sqlStatement);