Sum of grouped COUNT in SQL Query

sql

sql-queries

group-by

window-functions

byAlex Kataev·Dec 21, 2024

To swiftly retrieve the total SUM of grouped COUNT, use a subquery. Begin with grouping and counting in the subquery, then sum up in the outer query:

SELECT SUM(category_count) AS total_sum
FROM (
    SELECT COUNT(*) AS category_count
    FROM your_table
    GROUP BY category_column
) AS counts;

This SQL query groups your entries by category_column, counting each group's size, and accumulating these counts for the total sum.

Tips and tricks for effective querying

Tooling up with window functions

Window functions like OVER(), coupled with SUM and COUNT, can do magic:

SELECT
  name,
  COUNT(name) AS individual_count, -- Counting our sheep 🐑
  SUM(COUNT(name)) OVER() AS total_count -- Counting all the sheep in the field 🐑+🐑+🐑=😴
FROM your_table
GROUP BY name;

In the result, every row includes the total count across the dataset.

Navigating the sea of subtotals with ROLLUP

ROLLUP is your helpful SQL Server compass for creating subtotals and grand totals:

SELECT
  ISNULL(name, 'SUM') AS name_with_sum, -- If there's a NULL, call it 'SUM'
  COUNT(name) AS count
FROM your_table
GROUP BY name WITH ROLLUP; -- Add a row with totals. Because why not 👌

Making the best of COUNT versions

Default to COUNT(*) for row counting, but consider COUNT(1) for possible performance wins:

SELECT
  name,
  COUNT(1) AS count -- COUNT us in for better performance!
FROM your_table
GROUP BY name;

Nitty-Gritty FAQ and best practices

Coping with NULL and overall totals

How to handle NULL as an actual zero, and options for calculating totals.

Dealing with NULL using COALESCE

When NULL values need to be treated as zeros:

SELECT
  name,
  COUNT(COALESCE(some_nullable_column, 0)) AS count -- Because a NULL isn't a zero, unless you want it to be!
FROM your_table
GROUP BY name;

Calculating totals on the client-side

Sometimes your application layer may better suit the SUM of COUNT, especially with limitations on SQL complexity.

Points to ponder and caveats

Stay in sync with RDBMS-specific features

Your RDBMS's unique features can significantly transform a GROUP BY approach.

UNION ALL for summation

A second query with UNION ALL can insert a row for total sum:

SELECT name, COUNT(name) AS count
FROM your_table
GROUP BY name
UNION ALL
SELECT 'SUM', COUNT(name) -- Because sometimes you want it all (even the SUM) 🌐
FROM your_table;