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Optimizing Slow SQL Queries
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Optimizing Slow SQL Queries

HardSQL · PostgreSQL

Problem

How do you optimize a slow-running SQL query when dealing with millions of rows of transaction data?

Use the provided PostgreSQL tables to produce a representative optimized result for posted transactions in the first quarter of 2025. The query should calculate monthly account totals, prior-month totals, and each account's monthly rank.

Output

  1. One row per account and month, limited to the top three accounts in each month.
  2. Columns: month, account_id, account_name, monthly_amount, previous_month_amount, monthly_rank.
  3. Order by month, monthly_rank, and account_id.

Schema

transactions
ColumnTypeDescription
transaction_idPKINTUnique transaction identifier
account_idINTAccount associated with the transaction
category_idINTTransaction category identifier
transaction_dateTIMESTAMPTimestamp when the transaction occurred
statusVARCHAR(20)Transaction processing status
amountNUMERIC(14,2)Transaction amount
accounts
ColumnTypeDescription
account_idPKINTUnique account identifier
account_nameVARCHAR(120)Account display name
account_typeVARCHAR(40)Account classification
transaction_categories
ColumnTypeDescription
category_idPKINTUnique category identifier
category_nameVARCHAR(80)Transaction category name
category_groupVARCHAR(60)Higher-level category grouping
Tablestransactionsaccountstransaction_categories
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