Cardinality Estimation for a Predicate on a COUNT Expression
Paul White takes you on an optimizer journey, exploring how SQL Server comes up with cardinality estimates for COUNT queries.
2017-05-17
3,222 reads
Paul White takes you on an optimizer journey, exploring how SQL Server comes up with cardinality estimates for COUNT queries.
2017-05-17
3,222 reads
Aaron Bertrand shares some insight about early changes to Plan Explorer that help to provide you with the most accurate information we can.
2016-04-04
2,780 reads
The Query Optimiser needs a good estimate of the number of rows likely to be returned by each physical operator in order to select the best query plan from the most likely alternatives. Sometimes these estimates can go so wildly wrong as to result in a very slow query. Joe Sack shows how it can happen with SQL Queries on a data warehouse with a star schema.
2012-12-10
1,163 reads
By Brian Kelley
I will be leading an in-person Certified Information Systems Auditor (CISA) exam prep class...
EightKB is back again for 2026! The biggest online SQL Server internals conference is...
By HeyMo0sh
Working in DevOps long enough teaches you two universal truths: That’s exactly why I...
Hi all, I just started using VS Code to work with DB projects. I...
Comments posted to this topic are about the item Fun with JSON II
Comments posted to this topic are about the item Changing Data Types
I have some data in a table:
CREATE TABLE #test_data
(
id INT PRIMARY KEY,
name VARCHAR(100),
birth_date DATE
);
-- Step 2: Insert rows
INSERT INTO #test_data
VALUES
(1, 'Olivia', '2025-01-05'),
(2, 'Emma', '2025-03-02'),
(3, 'Liam', '2025-11-15'),
(4, 'Noah', '2025-12-22');
If I run this query, how many rows are returned?
SELECT t1.[key] AS row,
t2.*
FROM OPENJSON(
(
SELECT t.* FROM #test_data AS t FOR JSON PATH
)
) t1
CROSS APPLY OPENJSON(t1.value) t2; See possible answers