SQL Anti-Join for Missing Rows | Dataford Interview Questions

How would you write a SQL query to get all rows from one table that do not appear in another table, where one table key is a column in the other?

Use the provided tables and return every source row whose key has no matching value in the reference table.

Output

Return source_record_id, key_value, and source_label.
Include one row per qualifying source record, including source rows with a NULL key.
Order by source_record_id ascending.

source_records

Column	Type	Description
source_record_idPK	INT	Unique identifier for the source row
key_value	VARCHAR(20)	Key used to compare source and reference records
source_label	VARCHAR(100)	Descriptive label for the source row

reference_records

Column	Type	Description
reference_record_idPK	INT	Unique identifier for the reference row
key_value	VARCHAR(20)	Key that may match a source record
reference_label	VARCHAR(100)	Descriptive label for the reference row

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