How to select bottom most rows?

sql

performance

best-practices

sql-queries

byAlex Kataev·Sep 2, 2024

To select the last few rows, an ORDER BY clause is needed to reverse the sort order using DESC, and a LIMIT clause to specify the number of rows. For a SQL table YourTable, the below query fetches the bottom 3 records:

SELECT * FROM YourTable
ORDER BY id DESC
LIMIT 3;

Here id is the column that determines the "bottom" criteria. This SELECT statement will get you the last 3 entries in YourTable, just as the foot is the last part of the body to leave the building.

Detailed dissection of ORDER BY DESC & LIMIT

With the backdrop of selecting the bottom rows, it's integral to comprehend the synergy between ORDER BY and LIMIT clauses. ORDER BY clause allows sorting the data in two flavors, ascending (ASC) or descending (DESC) order based on one or more columns. LIMIT clause specifies the number of top records to return post-sorting – a powerful duo as rock-solid as Ant-Man and the Wasp!

Tackling large datasets

Dealing with large datasets, the ORDER BY DESC can have performance implications. Utilizing indexes or batch processing can minimize the performance impact akin to using a map – it helps you find the shortest path to fetch your data!

Real-world use-cases

Bottom row selections can be as unique as fingerprints. Financial transactions table might require fetching most recent transactions, and in a sensor data table, you might look for the latest readings. Tailor your query to suit your business needs and data usage patterns – remember, SQL skills are not one-size-fits-all!

Consideration for query accuracy

A key to note, ORDER BY DESC followed by LIMIT gives you the bottom rows for the sorted column — unless your data is being kittens-on-a-keyboard-style heavily manipulated. Active Data Manipulation Language (DML) operations might result in the "bottom" rows not reflecting the "last inserted" or "most recent" rows — a bit like trying to find the youngest child in a family where twins are born every year!

Advanced SQL Tricks for Bottom Rows

Systems that don't support LIMIT might use SELECT TOP (200) combined with ORDER BY and a subquery. A similar trick in SQL Server or MS Access is:

SELECT TOP 3 * FROM (
  SELECT TOP 100 PERCENT *
  FROM YourTable
  ORDER BY id DESC
) AS reversed
ORDER BY id ASC;

This first selects all rows in descending order and then applies TOP 3 in the subquery to return ascending order's bottom 3 rows — SQL equivalent of spoon bending!

Quick Performance Tips

Indexes on sorting columns can make ORDER BY operations faster than a cheetah!
Large datasets? Consider batch processing or paginated queries.
Caching strategies can be useful for frequently requested bottom rows.