Use one CTE many times

sql

prompt-engineering

best-practices

data-integrity

byAnton Shumikhin·Dec 26, 2024

WITH cte AS (
    -- Define CTE here: we love CTEs, yes we do!
)
SELECT * FROM cte  -- First taste
UNION ALL
SELECT * FROM cte; -- Second bite

Harness the power of UNION ALL to savor a CTE multiple times in a single bite. Neat, eh? This makes repeating the CTE flavors in your SQL recipe as easy as pie.

Going the extra mile: making your CTEs hard workers

Storing your CTE results for later

For those procrastinators among us, you can save your CTE results now and use them later:

WITH cte AS (
    -- Define your CTE: it works hard so you don't have to!
)
SELECT * INTO #TempTable FROM cte;

-- #TempTable: like a snack you can eat again and again!
SELECT * FROM #TempTable;
SELECT COUNT(*) FROM #TempTable;

Redefine and shine with Inline TVFs

Inline Table-Valued Functions (TVFs) let you re-use your CTEs like a dream:

CREATE FUNCTION dbo.GetCteData()
RETURNS TABLE AS
RETURN (
    -- Define CTE here: whoa, it's a new view—again!
)
-- Use the function as many times as you can:
SELECT * FROM dbo.GetCteData();

No more repeating yourself: let your CTE become a function and do the job over and over again.

Counting made easy and efficient

Embrace the dynamic duo of ROW_NUMBER() and COUNT() to make pagination and total row counting a piece of cake:

WITH cte AS (
    SELECT *,
           ROW_NUMBER() OVER(ORDER BY SomeColumn) AS RowNum, -- Paging made easy
           COUNT(1) OVER() AS TotalCount -- Count all the things!
    FROM SomeTable
)
SELECT *, TotalCount
FROM cte
WHERE RowNum BETWEEN @StartRow AND @EndRow; -- Just the slice you wanted

Pro tips: Advanced CTE usage

Performance and accuracy: the dynamic duo

Enhance your CTEs' rockstar performance:

Always test your stored procedures with different parameters: surprises are for birthdays, not coding.
Alias your CTEs properly to avoid awkward family reunions in your final query.

Dot your i's and cross your t's

Make sure you CTE references are as perfect as a cup of coffee on a rainy morning.
Validate your CTE joins and conditions: nobody likes unexpected guests showing up in results.

Less is more: Simplify your COUNT with CTE

Keep it simple and steady your hand for COUNT:

WITH cte AS (
    -- Define your perfect CTE: it's a beauty, isn't it?
)
SELECT COUNT(*) FROM cte; -- Less is more

Beyond usual: Overcoming CTE limitations

System restrictions: just a small hurdle!

Watch out for your database system restrictions: some systems like to play hard to get and might have limitations on the number of times a CTE can be referenced.

The importance of data integrity

Keep an eye on your data dependencies: foresee the impact of your actions when reusing CTE logic, as it might compromise your data integrity.

Calculations inside the CTE

When pagination requires it, don't be afraid to cast your results for needed calculations within the CTE.

Ordering for consistent pagination

Ensure a peaceful order in your results with the ROW_NUMBER() function:

WITH OrderedCTE AS (
    SELECT *, ROW_NUMBER() OVER(ORDER BY KeyColumn) AS RN
)
-- Just like rows in a garden: neat and orderly:
SELECT * FROM OrderedCTE WHERE RN BETWEEN @Start AND @End;