SQL Missing Values Count | Dataford Interview Questions

Your question is SQL Missing Values Count. Start with the requirements on the right.

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Problem

For a BCG X analytics workflow, records may contain incomplete values before they are processed. Given a collection of row records and a target column name, return how many rows have a missing value in that column.

Treat a value as missing when the column is absent from a row or its value is None. Do not treat valid values such as 0, False, or an empty string as missing.

Formal Specification

Implement count_missing_values(rows, column):

rows is a list of dictionaries, where each dictionary represents one record.
column is a string naming the column to inspect.
Return an integer equal to the number of rows where column is absent or mapped to None.
The input list and its dictionaries must not be modified.

Constraints

0 <= len(rows) <= 10^5
Each row contains string keys and arbitrary values
column is a non-empty string
The function must inspect each row at most once

Function Signature

def count_missing_values(rows, column):