# Querying a Database with ADO.NET: an overview

Every database query from C# takes three steps, connect, run the SQL, read the results, and each step has its own ADO.NET object.

Journeyman · C# · T-SQL · Updated November 3, 2026

## After this lesson you can

- Name the three steps of running a query from C#, and the ADO.NET object for each

## Key takeaways

- Every query from C# takes three steps: connect with a `SqlConnection`, run the SQL with a `SqlCommand`, and read the rows with a `SqlDataReader`.
- The SQL is a plain C# string. Get the query right in SSMS first, then paste it into your code.
- Open a connection, do the work, and close it as soon as you can. `using` closes each object for you.

With the driver and the connection string in place, a C# program can work with the database. Whatever the query, it always takes the same three steps:

| Step | What happens | ADO.NET object |
|---|---|---|
| 1. **Connect** | Open a connection to the database server | `SqlConnection` |
| 2. **Run the SQL** | Send a SQL statement over that connection | `SqlCommand` |
| 3. **Read the results** | Read the rows that come back, one at a time | `SqlDataReader` |

It's the same thing you do by hand in SSMS: connect to `localhost`, type a query and press F5, then read the results grid. ADO.NET does each of those steps in code.

## A first look

```csharp
using Microsoft.Data.SqlClient;

string connectionString = "Server=localhost;Database=Northwind;Integrated Security=true;TrustServerCertificate=true;";

// 1. Connect
using SqlConnection connection = new SqlConnection(connectionString);
connection.Open();

// 2. Run the SQL
string sql = "SELECT CategoryName FROM Categories ORDER BY CategoryName;";
using SqlCommand command = new SqlCommand(sql, connection);
using SqlDataReader reader = command.ExecuteReader();

// 3. Read the results
while (reader.Read())
{
    Console.WriteLine(reader.GetString(0));
}
```

```text
Beverages
Condiments
Confections
Dairy Products
Grains/Cereals
Meat/Poultry
Produce
Seafood
```

The SQL is a plain C# string, the same query you'd type in SSMS. A good habit: get the query right in SSMS first, then paste it into your code.

## Connections are borrowed, not kept

Opening a connection to a server takes time and uses the server's resources, so a program opens a connection, does its work, and closes it again as soon as it can. The `using` keyword in front of each object does the closing: when the program leaves the block, or here the end of the program, each object is **disposed**, and the connection is closed. You'll see `using` on every connection, command and reader.

## Check yourself

1 question to try on the lesson page.

## So what

Connect, run, read: every page that shows data from a database, in any app you build, starts with these three steps.

## Key terms

- [ADO.NET](https://www.ask-codey.com/glossary/adodotnet)
- [using Statement](https://www.ask-codey.com/glossary/using-statement)

## Cheat sheets

- [Querying a Database with ADO.NET: an overview](https://www.ask-codey.com/cheat-sheets/querying-a-database-with-ado-net-an-overview-cheat-sheet)

Source: https://www.ask-codey.com/lessons/querying-a-database-with-ado-net-an-overview