C# and PostgreSQL – Deleting Data

In order to delete data in a PostgreSQL database, the SQL ‘Delete’ statement needs to be used. The following example deletes a record with a specific ‘id’ from the ‘person’ table, which was used in the examples for selecting, inserting and updating data.

Deleting data works in a similar way to the other examples, where a parameterised query is used. Firstly, a connection to the database is established, then the query parameter for the ‘id’ of the record to be deleted is defined as a variable, which is bound in to the following SQL statement. The SQL statement is then executed and a confirmation message is displayed. The declaration and execution of the SQL statement is wrapped in a ‘try-catch-finally’ block to catch any errors that may arise and close the database connection at the end.

// Database connection variable.
NpgsqlConnection connect = new NpgsqlConnection(
    "Server=localhost;" +
    "Database=Demo;" +
    "User Id=DemoUN;" +
    "Password=DemoPW");

try
{

    // Connect to database.
    connect.Open();

}
catch (Exception e)
{

    // Message confirming unsuccessful database connection.
    Console.WriteLine("Database connection unsuccessful.");

    // Stop program execution.
    System.Environment.Exit(1);

}

try
{

    // Query parameters.
    int id = 2;

    // Query text.
    string sqlText = @"
        DELETE FROM person 
        WHERE id = @id
    ";

    // Query text incorporated into SQL command.
    NpgsqlCommand sqlDelete = new NpgsqlCommand(sqlText, connect);

    // Bind the parameter to the query.
    sqlDelete.Parameters.AddWithValue("@id", id);
    sqlDelete.Prepare();

    // Execute SQL.
    sqlDelete.ExecuteNonQuery();

    // Confirm successful deletion of person information.
    Console.WriteLine("Person information deleted successfully.");

}
catch (Exception e)
{

    // Confirm error deleting person information and exit.
    Console.WriteLine("Error deleting person information.");
    System.Environment.Exit(1);

}
finally
{

    // Close the database connection.
    connect.Close();

}

The contents of the ‘person’ table now looks as follows.

id firstname lastname title dob
1 Bob Smith Mr 1980-01-20
3 Fred Bloggs Mr 1975-05-07
4 Alan White Mr 1989-03-20
5 Fiona Bloggs Mrs 1985-05-19

Further Resources