How to get the first and last record from an SQL query?

Window Functions for Performance Turnaround

For super-sized data, ROW_NUMBER() window functions can be a nifty performance enhancer as compared to the UNION ALL method.

WITH RankedEmployees AS (
  -- Our performance spell: two-way ranking!
  SELECT *,
         ROW_NUMBER() OVER (ORDER BY hire_date ASC) AS rn_asc,
         ROW_NUMBER() OVER (ORDER BY hire_date DESC) AS rn_desc
  FROM employees
)
SELECT * FROM RankedEmployees
WHERE rn_asc = 1 OR rn_desc = 1;


Ascending and Descending: Two instances of ROW_NUMBER(). A CTE for Efficiency: The WITH clause (CTE) processes data just once. Dual Filters: WHERE rn_asc = 1 for the first record, rn_desc = 1 for the last.

Important: EXPLAIN ANALYZE is a nifty tool to compare query execution plans.

Query Performance Tuning

Efficient processing primarily depends on the dataset size and index optimization. Improper indexing on bulky data could turn these queries into performance bottlenecks.

• Swift Indexing: Craft indexes on columns used in ORDER BY clause.
• Query Cost Analysis: Use EXPLAIN ANALYZE to understand query execution plans.
• Scale Smarter: Consider data growth and corresponding performance impacts.

Proper indexing provides a performance boost, especially on ORDER BY columns.

Navigating Complex Queries

Even the simplest queries and functions can sometimes fail to capture the full complexity of real-world data. Condition handling and table joins come into play here.

• Table Joins: Embed JOIN statements in your CTE for deeper insights.
• Data Filtering: Enhance your WHERE clause to handle more conditions.
• Data Blending: Merge datasets with UNION ALL to create comprehensive reports.

Armed with SQL, you can confidently tackle everything from simple fetch queries to a complex web of queries gracefully.

Beyond First and Last

Often, you need to analyze more than just the first and last records. SQL's versatile functions like FIRST_VALUE and LAST_VALUE help traverse your dataset.

• Get Nearest Records: Find records adjacent to the last and first.
• Nth Record: Directly access the Nth record.
• Data Partitions: Use PARTITION BY to segment your data.

Not limited to extremes, SQL's function arsenal can map your entire dataset journey.