topic Re: Creating an SCD Type 2 Table with Auto CDC API (One-Time Load + Ongoing Updates) in Data Engineering

Creating an SCD Type 2 Table with Auto CDC API (One-Time Load + Ongoing Updates)

aonurdemir — Mon, 15 Sep 2025 12:45:56 GMT

Hello everyone,

I’m working with two CDC tables:

table_x: 23,467,761 rows (and growing)

table_y: 27,868,173,722 rows

My goal is to build an SCD Type 2 table (table_z) using the Auto CDC API.

The workflow I’d like to achieve is:

Initial Load: Populate table_z using the historical data from table_y (used only once).

Ongoing Updates: Once the initial load is complete, keep table_z updated using the incremental hourly data from table_x.

Constraints / Challenges:

I can usually handle append_flow + streaming tables, but I haven’t found a way to implement it cleanly with the Auto CDC API.

I don’t want to create a merged copy of table_x and table_y with append_flows just for the one-time bootstrap, since table_y is extremely large and would be wasteful to duplicate.

Has anyone set up a similar pattern? using a one-time full load from a large CDC table, followed by incremental Auto CDC updates from another table? If so, how did you approach it?

Thanks in advance!

Re: Creating an SCD Type 2 Table with Auto CDC API (One-Time Load + Ongoing Updates)

aonurdemir — Tue, 16 Sep 2025 07:43:02 GMT

I have solved it with the name parameter as this:

dlt.create_streaming_table(name="table_z")
dlt.create_auto_cdc_flow(
name="backfill",
target="table_z",
source="table_y",
keys=["user_id"],
sequence_by=col("source_ts_ms"),
ignore_null_updates=False,
apply_as_deletes=expr("op = 'd'"),
except_column_list=["op", "source_ts_ms"],
stored_as_scd_type="2",
track_history_column_list=["change_date"]
)

dlt.create_auto_cdc_flow(
name="update",
target="table_z",
source="table_x",
keys=["user_id"],
sequence_by=col("source_ts_ms"),
ignore_null_updates=False,
apply_as_deletes=expr("op = 'd'"),
except_column_list=["op", "source_ts_ms"],
stored_as_scd_type="2",
track_history_column_list=["change_date"]
)

Re: Creating an SCD Type 2 Table with Auto CDC API (One-Time Load + Ongoing Updates)

szymon_dybczak — Tue, 16 Sep 2025 07:44:16 GMT

Great @aonurdemir , thanks for sharing. Could you mark your answer as a solution?