Create a SQL query to retrieve most recent records

sql

sql-queries

performance-optimization

database-optimization

byAlex Kataev·Dec 14, 2024

Finding the most recent record in a category? The ROW_NUMBER() function is your trusty steed. Ride it over your unique identifier and order by the date field in descending order. Settle for the first row station.

SELECT * FROM (
    SELECT *, ROW_NUMBER() OVER (PARTITION BY category_id ORDER BY updated_at DESC) as rn
    -- You're first in line, Mr. Recent Record!
    FROM tableName
) t WHERE rn = 1;  -- Because no one remembers the second man on the moon. Sorry, Buzz.

Remember to swap tableName, category_id, updated_at with secret codes that open your table, unique identifier, and date column doors. This query brings home the bacon—the juiciest record for each group.

Query Breakdown

Let's decode this magical SQL scroll:

ROW_NUMBER() brands each record within a partition—in our case, each category_id—in a sequential order.
Sorting rows by updated_at in descending order ensures the fresher dates get served first.
The outer query is like a bouncer, granting entry to only the first row, aka the hippest of records.

Cutting Edge SQL Tricks

Dive deeper into the SQL toolbox when faced with Mt. Everest-sized datasets or Rubik's cube complex logic:

Derived Tables & Subqueries

Use a subquery to slice your dataset or calculate needed values before stitching it back to the main table.

Grouping for Efficiency

Large tables can be intimidating. Cozy up with grouping in subqueries to calculate maximum dates, saving processing time.

Slimming Down Columns

Trim the fat—only select essential fields in the final query for cleaner outputs and a speedier performance.

Optimizing Your Query

Step into the shoes of an SQL guru with these top-tier tricks:

Single Scan Subqueries

If you're reaching for subqueries, don't scan the same table redundantly. Get your goods in one sweep.

CTEs: Readability's Superhero

Common Table Expressions (CTEs) make your query look pretty and also help in structuring and debugging complex queries.

Bulletproof Data Accuracy

Double-check your date fields and consider using transaction IDs to prevent the heartache of duplicated entries.

Extra Shot of SQL Expresso

Need a little bit more kick? Here are some advanced moves:

Dynamic Query, Dynamic Results

WITH DateRanked AS (
    SELECT *, 
           ROW_NUMBER() OVER (PARTITION BY category_id ORDER BY updated_at DESC) as rn 
           -- We're really nailing this downward dog pose, aren't we?
    FROM tableName
)
SELECT *
FROM DateRanked
WHERE rn = 1 AND your_condition_here; -- Because you're unique, just like everybody else.

Swap your_condition_here with your custom conditions to make this query dance to your tune.

Temporal Tables: Time Travel Made Easy

If SQL Server 2016 (or its fresher cousins) is your jam, get chummy with system-versioned temporal tables:

They'll keep track of your history—No more writing those annoying join or window functions.
It feels good to just query the history table and call it a day.