# Using TSQL or Postgres

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## Switching to SQL Server or PostgreSQL

Rezoom.SQL translates its own dialect of SQL to different "backends". Currently [SQLite](https://www.sqlite.org/), MS SQL Server (T-SQL), and [PostgreSQL](https://www.postgresql.org/) are supported.

So far, this tutorial has stuck to SQLite. However, most apps in the .NET ecosystem store their data in SQL Server, so they use T-SQL.

### T-SQL

Note: if you want to use Postgres, just skip down the page. The Postgres section repeats any information you need from from this part.

If you're starting a fresh project and want to target T-SQL, it's as easy as installing [Rezoom.SQL.Provider.TSQL](https://www.nuget.org/packages/Rezoom.SQL.Provider.TSQL/) instead of [Rezoom.SQL.Provider.SQLite](https://www.nuget.org/packages/Rezoom.SQL.Provider.SQLite/). However, both packages are just thin wrappers around the [base library](https://www.nuget.org/packages/Rezoom.SQL.Provider/). They don't actually have any code, they just bundle some default config files and the initial `V1.model.sql`.

**With your existing project, you can easily change the config yourself** to target a different database backend. Here's how.

There's a file in your project called `rzsql.json`. Open it up and you'll see this:

```javascript
{
  "backend": "sqlite",
  "optionals":  "f#",
  "migrations": ".",
  "connectionname": "rzsql"
}
```

Just change the `"backend"` setting from `"sqlite"` to `"tsql"`. Then rebuild your project.

You may get build errors if you have queries using the `last_insert_rowid()` function. This is because that is a SQLite function, and doesn't exist in T-SQL. Rezoom.SQL unifies the syntax of SQL queries, but it's not a complete compatibility layer: the functions available are still determined by the backend. **In this case, the T-SQL equivalent function is `scope_identity()`**.

At this point your project should build, but you're not done yet. To be able to actually run the code, you'll need to create/edit your `AppSettings.json` with connection settings for SQL Server. This is *runtime* configuration whereas `rzsql.json` was *compile-time* information.

Here is an example AppSettings.json.

```json
{
  "ConnectionStrings": {
    "rzsql": "Data Source=rzsql.db"
  },
  "RezoomSQL": {
    "Providers": { "rzsql": "Microsoft.Data.Sqlite" }
  }
}
```

Change the `ConnectionStrings` and `RezoomSQL.Providers` sections like so:

```json
{
  "ConnectionStrings": {
    "rzsql": "Data Source=.\\SQLEXPRESS;Initial Catalog=rzsql;Integrated Security=SSPI;TrustServerCertificate=true"
  },
  "RezoomSQL": {
    "Providers": { "rzsql": "Microsoft.Data.SqlClient" }
  }
}
```

In the above configuration I am assuming your SQL server is located at .\SQLEXPRESS. If it isn't, change the connection string accordingly.

### Postgres

If you're starting a new project from scratch, you can just install [Rezoom.SQL.Provider.Postgres](https://www.nuget.org/packages/Rezoom.SQL.Provider.Postgres/) instead of [Rezoom.SQL.Provider.SQLite](https://www.nuget.org/packages/Rezoom.SQL.Provider.SQLite/).

But if you want to keep working on the project you already created, you can do that easily too:

There's a file in your project called `rzsql.json`. Open it up and you'll see this:

```javascript
{
  "backend": "sqlite",
  "optionals":  "f#",
  "migrations": ".",
  "connectionname": "rzsql"
}
```

Just change the `"backend"` setting from `"sqlite"` to `"postgres"`. Then rebuild your project.

You may get build errors if you have queries using the `last_insert_rowid()` function. This is because that is a SQLite function, and doesn't exist in Postgres. Rezoom.SQL unifies the syntax of SQL queries, but it's not a complete compatibility layer: the functions available are still determined by the backend. **In this case, the Postgres equivalent function is `lastval()`**.

At this point your project should build, but you're not done yet. To be able to actually run the code, you'll need to create/edit your `AppSettings.json` with connection settings for Postgres. This is *runtime* configuration whereas `rzsql.json` was *compile-time* information.

Here is an example AppSettings.json.

```json
{
  "ConnectionStrings": {
    "rzsql": "Data Source=rzsql.db"
  },
  "RezoomSQL": {
    "Providers": { "rzsql": "Microsoft.Data.Sqlite" }
  }
}
```

Change the `ConnectionStrings` and `RezoomSQL.Providers` sections like so. You'll need to fill in your own username and password in the connection string.

```json
{
  "ConnectionStrings": {
    "rzsql": "Host=localhost;Database=rzsql;Username=your_user_here;Password=your_password_here"
  },
  "RezoomSQL": {
    "Providers": { "rzsql": "Npgsql" }
  }
}
```

***

[← Adding migrations](/rezoom-sql/tutorial/addingmigrations.md) | [Loading nested objects →](/rezoom-sql/tutorial/loadingnestedobjects.md)


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