topic Re: Append to a record when updating Delta Table in Data Engineering

Append to a record when updating Delta Table

Serhii — Wed, 21 Sep 2022 10:40:15 GMT

I am updating the delta table in Databricks as follows

    segments_data.alias('segments_old').merge(
        segments_data_new.alias("updates"),
        "segments_old.source_url = updates.source_url",
    ).whenMatchedUpdate(
        set={"segments": "segments_old.segments"  + "updates.segments"  } # <- the line is pseudocode, don't know correct API
    ).whenNotMatchedInsertAll().execute()

where "segments" is a list of StructType

    StructField(
      "segments",
      StructType(
        [ ....

How can I append to the existing list - namely append to "segments" column in segments_old from updates within "whenMatchedUpdate"?

Instead of replacing - say "segments": "updates.segments" I would like to append "segments": "segments_old.segments" + "updates.segments"

Thanks for suggestions in advance!

Re: Append to a record when updating Delta Table

Hubert-Dudek — Wed, 21 Sep 2022 19:21:33 GMT

Set is just the equivalent of SQL UPDATE SET, so it sets a value from one table to a value from the expression.

So you can use built-in functions like col or exp:

from pyspark.sql.functions import *
...
set = { 'gender': col('segments_old.segments') + col('updates.segments') }
OR
set = { 'gender': exp('segments_old.segments + updates.segments') }

Re: Append to a record when updating Delta Table

Anonymous — Mon, 03 Oct 2022 06:24:30 GMT

Hi @Sergii Ivakhno

Hope all is well! Just wanted to check in if you were able to resolve your issue and would you be happy to share the solution or mark an answer as best? Else please let us know if you need more help.

We'd love to hear from you.

Thanks!

Re: Append to a record when updating Delta Table

Serhii — Tue, 01 Nov 2022 16:58:01 GMT

Yes it worked for us - thanks 🙂