You have an Azure Databricks workspace that is enabled for Unity Catalog and contains two...

The correct answer is A — INSERT INTO.

INSERT INTO appends all rows from the source to the target. Existing rows in table2 are untouched — the historical data stays intact — and the current year's rows from table1 are added. That is exactly what the requirement asks: 'preserve any existing data and minimise processing effort.'

Option B (CREATE TABLE AS SELECT) would fail if table2 already exists, or if used with CREATE OR REPLACE it wipes table2 entirely before writing — historical data gone. Option C (INSERT OVERWRITE) replaces the entire table content with only the table1 rows, also destroying table2's existing data. Option D (CREATE OR REPLACE TABLE AS SELECT) explicitly drops and recreates the table, eliminating all historical records.

INSERT INTO is deliberately the simplest possible command here — one line, no special options, no risk of accidental data loss.