Append to a record when updating Delta Table

[Serhii]

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!

[Hubert-Dudek]

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') }

 

[Anonymous]

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!

[Serhii]

Yes it worked for us - thanks 🙂