Group BY + CASE statement

sql

best-practices

join

sql-queries

byAnton Shumikhin·Jan 23, 2025

SELECT
  CASE
    WHEN column_x < 10 THEN 'Small'
    WHEN column_x >= 10 AND column_x < 20 THEN 'Medium'
    ELSE 'Large'
  END AS SizeCategory,
  COUNT(*) AS Quantity
FROM
  items
GROUP BY
  SizeCategory;

Leveraging the dynamic SizeCategory, we GROUP BY this category, tagging items based on their column_x value, then COUNT() tallies items within each SizeCategory.

Mastering `GROUP BY + CASE` combo

The CASE statement adds a powerful twist to the GROUP BY clause, enriching your data without complicating the query structure. Following certain practices can avoid common pitfalls and boost query efficiency and readability.

Aliasing: No Clone Wars here

Use unique column aliases to avoid naming conflicts. Plus, try dodging reserved words in SQL. It's like taking different routes to the same location, only faster and safer.

Positional references: Keeping track without losing track

While positional references may be useful in ORDER BY, using them in GROUP BY can lead to confusion (even SQL gets dizzy!). For JOINs, be explicit — clarity is key!

Group Sum: Counting made fancy

SUM(CASE WHEN) for aggregate counts helps keep GROUP BY free from unnecessary complexity — it's like counting apples and oranges, without mixing them up.

KISS (Keep It Simple, SQL)

Because, let’s face it — nobody likes to read walls of code. Rewrite and simplify your queries. This not only makes your SQL look good, but also easy to maintain. Now, isn’t that neat?

Filtering: The right time and place

Not all time is created equal! Use TIME filters as needed and be accurate. For complex CASE logic, think about OUTER APPLY with derived tables. Imagine it’s your personal butler, organizing your chaotic SQL mansion.

Be a Pro: Advanced Tips

Radioactive Constants: Handle with Care

If you've got constant values lurking in your GROUP BY, remove them (gently, now). They don't help with aggregation, and might just bog down your SQL cruiser.

Order in the Court (Results)

Logical ordering of results is your friend, and so are non-aggregate columns in your GROUP BY. Features on SQL are like tools in your coding belt — use them wisely!

Encapsulation: No Freedom for `CASE`

Encapsulate Case? Yes, even CASE needs some boundaries. It simplifies the structure and makes future joins easier. Encapsulation — everyone's happy!

Syntax & Comparisons: Squad Goals

Adhere to proper syntax, use comparison operators diligently. Your data integrity is priceless, and so is the SQL official documentation. Keep 'em close!

Keep Calm and Query On

Review and refine your SQL queries. As your understanding deepens and data evolves, your SQL should evolve too. Make brevity, clarity and maintenance your mantra.

explain-codes / Sql / Group BY + CASE statement

Linked

Using group by on two fields and count in SQL



How to use count and group by at the same select statement



Ora-00979 not a group by expression



Sql COUNT* GROUP BY bigger than



Mysql Group By and Sum total value of other column

