Maximizing Aggregation Query Speed with Covering Indexes in MySQL

Optimize Query with Covering Index for Aggregation

Write a MySQL query that selects only indexed columns in an aggregation query from the Orders table to benefit from a covering index.

Solution:

-- Select indexed columns to take advantage of a covering index.
SELECT CustomerID, COUNT(OrderID) AS OrderCount
FROM Orders
GROUP BY CustomerID;

Explanation:

• Purpose of the Query:
• To execute an aggregation query efficiently by retrieving only indexed columns.
• Leveraging a covering index minimizes the need to access the full table data.
• Key Components:
• COUNT(OrderID) AS OrderCount : Aggregates the number of orders per customer.
• GROUP BY CustomerID : Groups the result set by customer.
• Real-World Application:
• Often used in generating summary reports where speed is critical.

Notes:

• Ensure a covering index exists that includes both CustomerID and OrderID.
• Covering indexes can greatly reduce disk I/O and improve query speed.

For more Practice: Solve these Related Problems:

• Write a MySQL query that selects only indexed columns in an aggregation query from the Sales table to benefit from a covering index.
• Write a MySQL query that selects only indexed columns in an aggregation query from the Projects table to benefit from a covering index.
• Write a MySQL query that selects only indexed columns in an aggregation query from the Orders table to benefit from a covering index.
• Write a MySQL query that selects only indexed columns in an aggregation query from the Transactions table to benefit from a covering index.

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Previous MySQL Exercise: Force Index usage in a JOIN Query with Index Hints.
Next MySQL Exercise: Analyze Performance of a Correlated Subquery with EXPLAIN.