Moving Data from SQL Server to Postgres with NiFi

Kelson V — Mon, 26 Jan 2026 15:05:02 +0000

Learn how to build a containerized ETL pipeline using Apache NiFi to move data from SQL Server to PostgreSQL, featuring fixes for JDBC driver setup and timestamp type mismatches.

I recently set up a pipeline to move sales records from SQL Server to PostgreSQL using NiFi and Docker.

It’s a standard task, but there are a few manual steps and annoying errors that I had to fix. Here is exactly how I did it.

Why move the data?

Basically, you don't want to run heavy analytics on your main SQL Server while people are trying to use it. Moving the data to a separate Postgres database keeps things fast for everyone.

The Setup

I ran everything in Docker so I didn't have to install stuff on my actual computer:

SQL Server: Where the data starts.
Postgres: Where the data ends up.
NiFi: The tool that moves the data.

Step 1: Getting the Drivers Ready

NiFi is a Java app and doesn't know how to talk to these databases by default. You have to manually give it the JDBC driver files (the .jar files).

Download the drivers here:

SQL Server: https://learn.microsoft.com/en-us/sql/connect/jdbc/download-microsoft-jdbc-driver-for-sql-server
Postgres: https://jdbc.postgresql.org/download/

Since everything is in Docker, I used these commands to "push" the drivers into the NiFi container:

docker cp C:\drivers\mssql-jdbc-13.2.1.jre11.jar nifi-orchestrator:/opt/nifi/nifi-current/lib/
docker cp C:\drivers\postgresql-42.7.9.jar nifi-orchestrator:/opt/nifi/nifi-current/lib/

Note: You have to restart the NiFi container after this or it won't see the drivers.

Step 2: Setting up the NiFi Flow

I used three main boxes (processors) to get this done:

GenerateTableFetch: This checks SQL Server for new rows. I set the Maximum-value Column to id. This is important because it tells NiFi: "Only grab rows with an ID higher than the last one we moved." No duplicates.
ExecuteSQL: This actually pulls the data.
PutDatabaseRecord: This sends the data into the Postgres table (stg_sales).

Step 3: Fixing the Timestamp Error

This was the only real problem I hit. Postgres is very picky about dates. By default, NiFi sends dates as plain text, which makes Postgres crash with a character varying error.

The Fix: Go to the ExecuteSQL properties and set Use Avro Logical Types to true. This makes sure the date stays a "date" so Postgres accepts it.

Step 4: How to Reset for Testing

If you want to test the flow again with the same data, NiFi won't move it because it "remembers" the last ID.

Stop the processor.
Right-click → View State.
Click Clear State.

Also, don't leave the Run Schedule at 0 sec. Set it to 10 sec so it doesn't max out your CPU.

Conclusion

Once everything was green, I checked DBeaver and the data was all there. It’s a simple setup once you get the drivers and the timestamp setting right.

DEV Community: Kelson V