---
metadata:
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    content: Diplodoc Platform v5.50.6
alternate:
  - https://ydb.tech/docs/en/concepts/query_execution/federated_query/ms_sql_server.md?version=main
  - https://ydb.tech/docs/ru/concepts/query_execution/federated_query/ms_sql_server.md?version=main
sourcePath: en/core/concepts/query_execution/federated_query/ms_sql_server.md
---
> **Documentation Index:** Fetch the complete configuration index at https://ydb.tech/docs/en/llms.txt

# Working with Microsoft SQL Server databases

<!-- source: en/concepts/query_execution/federated_query/_includes/experimental_connectors_warning.md -->
{% note warning %}

External connectors are an experimental feature of YDB. To work with external DBMS through connectors, you need to deploy [fq-connector-go](https://ydb.tech/docs/en/devops/deployment-options/manual/federated-queries/connector-deployment.md?version=main#fq-connector-go) and explicitly enable the corresponding sources in the cluster configuration YDB. The functionality may change, so use in production is not recommended without thorough testing.

{% endnote %}
<!-- endsource: en/concepts/query_execution/federated_query/_includes/experimental_connectors_warning.md -->

This section describes the basic information about working with an external [Microsoft SQL Server](https://learn.microsoft.com/ru-ru/sql/?view=sql-server-ver16) database.

To work with an external Microsoft SQL Server database, you need to perform the following steps:

1. Create a [secret](https://ydb.tech/docs/en/concepts/datamodel/secrets.md?version=main) containing the password for connecting to the database.


   ```yql
   CREATE SECRET ms_sql_server_datasource_user_password WITH (value = "<password>");
   ```

2. Create an [external data source](https://ydb.tech/docs/en/concepts/datamodel/external_data_source.md?version=main) that describes a specific Microsoft SQL Server database. The `LOCATION` parameter contains the network address of the Microsoft SQL Server instance to which the connection is made. The `DATABASE_NAME` parameter specifies the database name (for example, `master`). The values of the `LOGIN` and `PASSWORD_SECRET_PATH` parameters are used for authentication to the external database. You can enable encryption of connections to the external database using the `USE_TLS="TRUE"` parameter.


   ```yql
   CREATE EXTERNAL DATA SOURCE ms_sql_server_datasource WITH (
       SOURCE_TYPE="MsSQLServer",
       LOCATION="<host>:<port>",
       DATABASE_NAME="<database>",
       AUTH_METHOD="BASIC",
       LOGIN="user",
       PASSWORD_SECRET_PATH="ms_sql_server_datasource_user_password",
       USE_TLS="TRUE"
   );
   ```

3. <!-- source: en/concepts/query_execution/federated_query/_includes/connector_deployment.md -->
   Deploy the [connector](https://ydb.tech/docs/en/concepts/query_execution/federated_query/architecture.md?version=main#connectors)  and [configure](https://ydb.tech/docs/en/devops/deployment-options/manual/federated-queries/index.md?version=main)  the YDB dynamic nodes to interact with it. Additionally, ensure network access from the YDB dynamic nodes to the external data source (at the address specified in the `LOCATION` parameter of the `CREATE EXTERNAL DATA SOURCE` request). If network connection encryption to the external source was enabled in the previous step, the connector will use the system's root certificates. More details on TLS configuration can be found in the [guide](https://ydb.tech/docs/en/devops/deployment-options/manual/federated-queries/connector-deployment.md?version=main) on deploying the connector.
   <!-- endsource: en/concepts/query_execution/federated_query/_includes/connector_deployment.md -->
4. [Execute a query](#query) on the database.

## Query syntax {#query}

The following SQL query form is used to work with Microsoft SQL Server:


```yql
SELECT * FROM ms_sql_server_datasource.<table_name>
```


where:

- `ms_sql_server_datasource`: external data source identifier
- `<table_name>` is the name of the table inside the external data source.

## Limitations {#limitations}

When working with Microsoft SQL Server clusters, there are a number of limitations:

1. <!-- source: en/concepts/query_execution/federated_query/_includes/supported_requests.md -->
   External sources are available only for reading data through `SELECT` queries. The federated query processing engine currently does not support queries that modify tables in external sources.
   <!-- endsource: en/concepts/query_execution/federated_query/_includes/supported_requests.md -->
2. <!-- source: en/concepts/query_execution/federated_query/_includes/datetime_limits.md -->
   If the date value stored in the external data source is outside the allowed range for YDB (all dates used must be later than 1970-01-01 but earlier than 2105-12-31), such a value in YDB will be converted to `NULL`.
   <!-- endsource: en/concepts/query_execution/federated_query/_includes/datetime_limits.md -->
3. <!-- source: en/concepts/query_execution/federated_query/_includes/predicate_pushdown_preamble.md -->
   The YDB federated query processing system is capable of delegating the execution of certain parts of a query to the system acting as the data source. Query fragments are passed through YDB directly to the external system and processed by them. This optimization, known as "predicate pushdown", significantly reduces the amount of data transferred from the source to the federated query processing engine. This reduces network load and saves computational resources for the federated YDB.

   A specific case of predicate pushdown, when the filtering expressions are specified after the `WHERE` keyword, are passed to the data source, is called "filter pushdown". Filter pushdown is possible when using:
   <!-- endsource: en/concepts/query_execution/federated_query/_includes/predicate_pushdown_preamble.md -->

   <!-- source: en/concepts/query_execution/federated_query/_includes/predicate_pushdown_examples.md -->
   |Description|Example|
   |---|---|
   |`NULL` checks|`WHERE column1 IS NULL` or `WHERE column1 IS NOT NULL`|
   |Logical conditions `OR`, `NOT`, `AND` and parentheses for controlling calculation priority. |`WHERE column1 IS NULL OR (column2 IS NOT NULL AND column3 > 10)`.|
   |[Comparison operators](../../../yql/reference/syntax/expressions.md#comparison-operators) with other columns or constants. |`WHERE column1 > column2 OR column3 <= 10`, `WHERE column1 + column2 > 10`, `WHERE column1 = (10 + 10)`|

   When using other types of filters, pushdown to the data source is not performed: filtering of the external table rows will be executed by the federated YDB, which means that YDB will perform a full scan of the external table when processing the query.
   <!-- endsource: en/concepts/query_execution/federated_query/_includes/predicate_pushdown_examples.md -->

   | Data type YDB |
   | --- |
   | `Bool` |
   | `Int8` |
   | `Int16` |
   | `Int32` |
   | `Int64` |
   | `Float` |
   | `Double` |

## Supported data types

In a Microsoft SQL Server database, the optionality flag of column values (whether the column is allowed or prohibited from containing `NULL` values) is not part of the data type system. The `NOT NULL` constraint for any column of any table is stored as the value of the `IS_NULLABLE` column of the [INFORMATION_SCHEMA.COLUMNS](https://learn.microsoft.com/ru-ru/sql/relational-databases/system-information-schema-views/columns-transact-sql?view=sql-server-ver16) system table, that is, at the table metadata level. Consequently, all basic Microsoft SQL Server data types can by default contain `NULL` values, and in the YDB type system they must be mapped to [optional](https://ydb.tech/docs/en/yql/reference/types/optional.md?version=main) types.

Below is a table of correspondence between Microsoft SQL Server types and YDB. All other data types, except those listed, are not supported.

| Microsoft SQL Server data type | Data type YDB | Notes |
| --- | --- | --- |
| `bit` | `Optional<Bool>` |  |
| `tinyint` | `Optional<Int8>` |  |
| `smallint` | `Optional<Int16>` |  |
| `int` | `Optional<Int32>` |  |
| `bigint` | `Optional<Int64>` |  |
| `real` | `Optional<Float>` |  |
| `float` | `Optional<Double>` |  |
| `date` | `Optional<Date>` | Valid date range from 1970-01-01 to 2105-12-31. If the value goes beyond the range boundaries, `NULL` is returned. |
| `smalldatetime` | `Optional<Datetime>` | Valid time range from 1970-01-01 00:00:00 to 2105-12-31 23:59:59. If the value goes beyond the range boundaries, the value `NULL` is returned. |
| `datetime` | `Optional<Timestamp>` | Valid time range from 1970-01-01 00:00:00 to 2105-12-31 23:59:59. If the value goes beyond the range boundaries, the value `NULL` is returned. |
| `datetime2` | `Optional<Timestamp>` | Valid time range from 1970-01-01 00:00:00 to 2105-12-31 23:59:59. If the value goes beyond the range boundaries, the value `NULL` is returned. |
| `binary` | `Optional<String>` |  |
| `varbinary` | `Optional<String>` |  |
| `image` | `Optional<String>` |  |
| `char` | `Optional<Utf8>` |  |
| `varchar` | `Optional<Utf8>` |  |
| `text` | `Optional<Utf8>` |  |
| `nchar` | `Optional<Utf8>` |  |
| `nvarchar` | `Optional<Utf8>` |  |
| `ntext` | `Optional<Utf8>` |  |