Slide 25
Slide 25 text
SQL 2 SQL 1
Entity Framework Core
Performance-Optimierung aus der Praxis
Lets try with SQL …
Understanding Queries
SELECT
( SELECT TOP(1) p.Id FROM Products p WHERE s.Id = p.StudioId ORDER BY p.Id) AS FirstProductId,
( SELECT TOP(1) p.Name FROM Products p WHERE s.Id = p.StudioId ORDER BY p.Id) AS FirstProductName
FROM
Studios s
SELECT p.Id, p.Name
FROM
Studios s
LEFT JOIN
(
SELECT Id, Name, StudioId
FROM
(
SELECT Id, Name, StudioId, ROW_NUMBER() OVER(PARTITION BY StudioId ORDER BY Id) AS row
FROM Products
) p
WHERE row <= 1
) p ON s.Id = p.StudioId
2 sub-selects
Window function
“ROW_NUMBER”