Mask Phone Numbers — Solution & ExplanationProblems / Mask Phone Numbers / EditorialApproach

Slice off the last 4 characters with substr(phone, 7) — for a 10-character string, position 7 through the end is exactly the last 4 digits.

Prepend the literal mask with string concatenation: 'XXXXXX' || substr(phone, 7).

Order by customer_id.

In PySpark the same shape is F.concat(F.lit('XXXXXX'), F.substring('phone', 7, 4)).Key InsightPhone numbers must be handled as strings, not integers — casting to a number silently drops leading zeros (0225554321 would shrink to 9 digits and the mask would slip by one character). Because the width is fixed at 10, no regex is needed: positional slicing is simpler and faster.Hints

You never need the first 6 digits — only characters 7 through 10 survive the mask, so this is string slicing, not pattern replacement.

In DuckDB, substr(phone, 7) returns everything from the 7th character to the end; glue the mask on with 'XXXXXX' || ...

In PySpark, F.substring('phone', 7, 4) grabs the last 4 characters; combine with F.concat and F.lit('XXXXXX').

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