MSSQL
Microsoft SQL Server is a proprietary relational database management system developed by Microsoft.
The SQL Server Wrapper allows you to read data from Microsoft SQL Server within your Postgres database.
Preparation
Before you can query SQL Server, you need to enable the Wrappers extension and store your credentials in Postgres.
Enable Wrappers
Make sure the wrappers extension is installed on your database:
_10create extension if not exists wrappers with schema extensions;
Enable the SQL Server Wrapper
Enable the mssql_wrapper FDW:
_10create foreign data wrapper mssql_wrapper_10 handler mssql_fdw_handler_10 validator mssql_fdw_validator;
Store your credentials (optional)
By default, Postgres stores FDW credentials inside pg_catalog.pg_foreign_server in plain text. Anyone with access to this table will be able to view these credentials. Wrappers is designed to work with Vault, which provides an additional level of security for storing credentials. We recommend using Vault to store your credentials.
_10-- Save your SQL Server connection string in Vault and retrieve the `key_id`_10insert into vault.secrets (name, secret)_10values (_10 'mssql',_10 'Server=localhost,1433;User=sa;Password=my_password;Database=master;IntegratedSecurity=false;TrustServerCertificate=true;encrypt=DANGER_PLAINTEXT;ApplicationName=wrappers'_10)_10returning key_id;
The connection string is an ADO.NET connection string, which specifies connection parameters in semicolon-delimited string.
Supported parameters
All parameter keys are handled case-insensitive.
| Parameter | Allowed Values | Description |
|---|---|---|
| Server | <string> | The name or network address of the instance of SQL Server to which to connect. Format: host,port |
| User | <string> | The SQL Server login account. |
| Password | <string> | The password for the SQL Server account logging on. |
| Database | <string> | The name of the database. |
| IntegratedSecurity | false | Windows/Kerberos authentication and SQL authentication. |
| TrustServerCertificate | true, false | Specifies whether the driver trusts the server certificate when connecting using TLS. |
| Encrypt | true, false, DANGER_PLAINTEXT | Specifies whether the driver uses TLS to encrypt communication. |
| ApplicationName | <string> | Sets the application name for the connection. |
Connecting to SQL Server
We need to provide Postgres with the credentials to connect to SQL Server. We can do this using the create server command:
_10create server mssql_server_10 foreign data wrapper mssql_wrapper_10 options (_10 conn_string_id '<key_ID>' -- The Key ID from above._10 );
Create a schema
We recommend creating a schema to hold all the foreign tables:
_10create schema if not exists mssql;
Options
The full list of foreign table options are below:
table- Source table or view name in SQL Server, required.
This can also be a subquery enclosed in parentheses, for example,
_10table '(select * from users where id = 42 or id = 43)'
Entities
SQL Server Tables
This is an object representing SQL Server tables and views.
Ref: Microsoft SQL Server docs
Operations
| Object | Select | Insert | Update | Delete | Truncate |
|---|---|---|---|---|---|
| table/view | ✅ | ❌ | ❌ | ❌ | ❌ |
Usage
_10create foreign table mssql.users (_10 id bigint,_10 name text,_10 dt timestamp_10)_10 server mssql_server_10 options (_10 table 'users'_10 );
Notes
- Supports both tables and views as data sources
- Can use subqueries in the
tableoption - Query pushdown supported for:
whereclausesorder byclauseslimitclauses
- See Data Types section for type mappings between PostgreSQL and SQL Server
Query Pushdown Support
This FDW supports where, order by and limit clause pushdown.
Supported Data Types
| Postgres Type | SQL Server Type |
|---|---|
| boolean | bit |
| char | tinyint |
| smallint | smallint |
| real | float(24) |
| integer | int |
| double precision | float(53) |
| bigint | bigint |
| numeric | numeric/decimal |
| text | varchar/char/text |
| date | date |
| timestamp | datetime/datetime2/smalldatetime |
| timestamptz | datetime/datetime2/smalldatetime |
Limitations
This section describes important limitations and considerations when using this FDW:
- Large result sets may experience slower performance due to full data transfer requirement
- Only supports specific data type mappings between Postgres and SQL Server
- Only support read operations (no INSERT, UPDATE, DELETE, or TRUNCATE)
- Windows authentication (Integrated Security) not supported
- Materialized views using these foreign tables may fail during logical backups
Examples
Basic Example
First, create a source table in SQL Server:
_11-- Run below SQLs on SQL Server to create source table_11create table users (_11 id bigint,_11 name varchar(30),_11 dt datetime2_11);_11_11-- Add some test data_11insert into users(id, name, dt) values (42, 'Foo', '2023-12-28');_11insert into users(id, name, dt) values (43, 'Bar', '2023-12-27');_11insert into users(id, name, dt) values (44, 'Baz', '2023-12-26');
Then create and query the foreign table in PostgreSQL:
_11create foreign table mssql.users (_11 id bigint,_11 name text,_11 dt timestamp_11)_11 server mssql_server_11 options (_11 table 'users'_11 );_11_11select * from mssql.users;
Remote Subquery Example
Create a foreign table using a subquery:
_11create foreign table mssql.users_subquery (_11 id bigint,_11 name text,_11 dt timestamp_11)_11 server mssql_server_11 options (_11 table '(select * from users where id = 42 or id = 43)'_11 );_11_11select * from mssql.users_subquery;