Merge Operation in delta table in databricks update records shows wrong information.

Question

Hi all,

I am performing merge operation on my delta table in spark databricks

my existing delta table is dlt_salary, it already has some records

Now i created another dataframe followed by new source using tempView which is going to use as updated source as df_source in merge statement.
Now my updated source table is df_source -->Please check the snips

here if you see i have one record is updated and One newly inserted

After merge Operation The count should show updated 1 and inserted 1

but its not showing the desired thing ,I am confused in the log table created after merge statement.
Please help me to understand what's going on behind the scenes.

Answer 1

Hello @Vaibhav B ,
Thanks for the question and using MS Q&A platform.
As we understand the ask here is how the MERGE operatios works, please do let us know if its not accurate.

You said

After merge Operation The count should show updated 1 and inserted 1

But the snashot says Updated -3

Let me share what i think is going on .

We are clear about the INSERT part , as we have 1 ID ( ID 4 , Viraj ) which is not in the dlt_salary table and so the INSERT happens for this record .
For the update , the dlt_salary and df_source have 3 records which are common ( matched i should say ID , 1,2,3 ) and so three records are updated .
Behind the scene MERGE command is combination of INSERT and UPDATE statement on match records .

Please do let me if you have any queries.
Thanks
Himanshu

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