025_fill_missing_client_data.md

SQL Everyday #025

Fill Missing Client Data

Site: DataLemur
Difficulty per Site: Medium

Problem

When accessing Accenture's retailer client's database, you observe that the category column in products table contains null values.

Write a query that returns the updated product table with all the category values filled in, taking into consideration the assumption that the first product in each category will always have a defined category value. [Full Description]

Submitted Solution

-- Submitted Solution
WITH cte AS (
  SELECT
    *
    ,COUNT(category) OVER (ORDER BY product_id) AS numbered_category
  FROM products
)
SELECT
  product_id
  ,FIRST_VALUE(category) OVER (PARTITION BY numbered_category) AS category
  ,name
FROM cte
;

Site Solution

-- DataLemur Solution 
WITH filled_category AS (
SELECT
  *,
  COUNT(category) OVER (ORDER BY product_id) AS numbered_category
FROM products
)

SELECT
  product_id,
  COALESCE(category, MAX(category) OVER (PARTITION BY numbered_category)) AS category,
  name
FROM filled_category;

Notes

• I had to check DataLemur's hint to solve this problem. Interesting use of COUNT() and window function for assigning new categories but could only work with the given assumption.

NB

FIRST_VALUE()

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