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Optimizing Slow SQL Queries
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Optimizing Slow SQL Queries

HardSQL · PostgreSQL

Problem

Tell me how you approach optimizing a slow-running SQL query or join-heavy operation.

Using the provided PostgreSQL schema and sample data, describe your diagnosis and submit an optimized query that returns the required result set. Your answer should address execution plans, filtering, join behavior, aggregation, and indexing considerations.

Output

  1. One row per qualifying customer or unassigned order owner.
  2. Columns: customer_name, order_count, and gross_value.
  3. Include completed January 2025 orders with positive gross value. Sort by gross_value descending, then customer_name ascending.

Schema

customers
ColumnTypeDescription
customer_idPKINTUnique customer identifier
customer_nameVARCHAR(100)Customer display name
orders
ColumnTypeDescription
order_idPKINTUnique order identifier
customer_idINTCustomer associated with the order
order_dateDATEDate the order was placed
statusVARCHAR(20)Current order status
order_items
ColumnTypeDescription
item_idPKINTUnique order item identifier
order_idINTOrder containing the item
quantityINTNumber of units ordered
unit_priceNUMERIC(10,2)Price per unit
Tablescustomersordersorder_items
Interviewer

Your question is Optimizing Slow SQL Queries. Start with the requirements and the three tables in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.

You need to log in / sign up to run or submit.
CodePostgreSQL
Sign up free to run your codeLog inLn 1
Run your query to see results here.