Round #800

Use UNION to combine current_employees and former_employees, marking source.

```csharp using System; using System.Data; class Program { static void Main() { // Create data tables DataTable currentEmployees = new DataTable(); currentEmployees.Columns.Add("Name", typeof(string)); currentEmployees.Columns.Add("Age", typeof(int)); currentEmployees.Columns.Add("Department", typeof(string)); currentEmployees.Rows.Add("John", 34, "Sales"); currentEmployees.Rows.Add("Jane", 28, "Marketing"); currentEmployees.Rows.Add("Alice", 32, "HR"); DataTable formerEmployees = new DataTable(); formerEmployees.Columns.Add("Name", typeof(string)); formerEmployees.Columns.Add("Age", typeof(int)); formerEmployees.Columns.Add("Department", typeof(string)); formerEmployees.Rows.Add("Bob", 35, "Engineering"); formerEmployees.Rows.Add("Eve", 29, "Finance"); formerEmployees.Rows.Add("Charlie", 36, "Operations"); // Add a new column 'Source' to each data table currentEmployees.Columns.Add("Source", typeof(string)); formerEmployees.Columns.Add("Source", typeof(string)); // Fill the 'Source' column foreach (DataRow row in currentEmployees.Rows) { row["Source"] = "Current"; } foreach (DataRow row in formerEmployees.Rows) { row["Source"] = "Former"; } // Combine the two data tables DataTable combinedEmployees = new DataTable(); combinedEmployees.Merge(currentEmployees); combinedEmployees.Merge(formerEmployees); // Print the combined data table foreach (DataRow row in combinedEmployees.Rows) { Console.WriteLine($"{row["Name"]}\t{row["Age"]}\t{row["Department"]}\t{row["Source"]}"); } } } ```

```csharp using System; using System.Data; using System.Data.SqlClient; public class EmployeeRepository { private readonly string _connectionString; public EmployeeRepository(string connectionString) { _connectionString = connectionString; } public DataTable GetCombinedEmployees() { using (var connection = new SqlConnection(_connectionString)) { connection.Open(); var query = @" SELECT 'Current' AS Source, * FROM current_employees UNION ALL SELECT 'Former' AS Source, * FROM former_employees"; var adapter = new SqlDataAdapter(query, connection); var dataTable = new DataTable(); adapter.Fill(dataTable); return dataTable; } } } class Program { static void Main(string[] args) { var connectionString = "Server=myServerAddress;Database=myDataBase;User Id=myUsername;Password=myPassword;"; var repository = new EmployeeRepository(connectionString); var combinedEmployees = repository.GetCombinedEmployees(); foreach (DataRow row in combinedEmployees.Rows) { Console.WriteLine($"Source: {row["Source"]}, Name: {row["Name"]}"); } } } ```