SQL: Monthly Complaints With MoM | Dataford Interview Questions

Write a SQL query to calculate monthly service complaints by site, including the month-over-month change in complaints.

Use the service complaints data across all months represented by complaint dates. Include every site for every month in that range, including months with zero complaints. The first month for each site should have a NULL prior-month value and NULL change.

Output

One row per site and calendar month
Columns: site_name, month, complaint_count, previous_month_complaints, mom_change
Include all sites, including sites with no complaints
Order by site_name, then chronological month

Schema

sites

Column	Type	Description
site_idPK	INT	Unique facility identifier
site_name	VARCHAR(100)	Facility name
region	VARCHAR(50)	Operational region

service_complaints

Column	Type	Description
complaint_idPK	INT	Unique complaint identifier
site_id	INT	Site associated with the complaint
complaint_date	DATE	Date the complaint was received
category	VARCHAR(80)	Complaint category

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