SQL for Analytics - lesson 7 | HackIndia Skills

SQL for Analytics - lesson 7 | HackIndia Skills | HackIndia

Example

Checks query file

Add a file like checks.sql beside your main queries. Keep it boring and clear.

This example assumes a product_events table with event_id, user_id, event_name, created_at, and amount_inr.

-- checks.sql

-- 1. Row count and date range
SELECT
  COUNT(*) AS total_events,
  MIN(created_at) AS first_event_at,
  MAX(created_at) AS last_event_at
FROM product_events;

-- 2. Null checks for required fields
SELECT
  SUM(CASE WHEN event_id IS NULL THEN 1 ELSE 0 END) AS null_event_ids,
  SUM(CASE WHEN user_id IS NULL THEN 1 ELSE 0 END) AS null_user_ids,
  SUM(CASE WHEN event_name IS NULL THEN 1 ELSE 0 END) AS null_event_names,
  SUM(CASE WHEN created_at IS NULL THEN 1 ELSE 0 END) AS null_created_at
FROM product_events;

-- 3. Duplicate event IDs
SELECT
  event_id,
  COUNT(*) AS times_seen
FROM product_events
GROUP BY event_id
HAVING COUNT(*) > 1;

-- 4. Impossible payment values
SELECT
  COUNT(*) AS bad_payment_rows
FROM product_events
WHERE event_name = 'payment_success'
  AND (amount_inr IS NULL OR amount_inr <= 0);

-- 5. Simple payment user count for comparison
SELECT
  COUNT(DISTINCT user_id) AS users_with_successful_payment
FROM product_events
WHERE event_name = 'payment_success';

Example

Write checked outputs

In your project, save results from checks in a small text file or README section. This proves you did not only write queries.

Keep it short. Mention what passed and what you fixed.

Checked outputs

Dataset: sample_product_events.csv
Rows: 2,450 events
Date range: 2024-07-01 to 2024-07-31
Duplicate event_id rows: 0
Null user_id rows: 0
Bad payment_success amount rows: 0

Metric checked:
Funnel query payment_success users = 186
Simple distinct payment_success users = 186
Status: matches

Note:
Removed 4 test users from all insight queries using user_id NOT LIKE 'test_%'.

Check numbers before presenting

Trust is earned

What to check

Basic check flow

Checks query file

Do not hide mismatches

Use AI carefully

Write checked outputs

Do this now

Quick check