What is the processing order of logical parts of the following query?
SELECT ClientId, SUM(t2.Amount) total FROM cliens t1 JOIN orders t2 ON t1.ClientId = t2.ClientId WHERE ClientName Like 'John%' GROUP BY ClientId HAVING t2.Amount > 100 ORDER BY total DESC LIMIT 1
Experience Level: Medior
Tags: DatabasesSQL
Answer
The database engine processes the query in the following order:
- FROM and JOINs - determines and filters the rows using criteria in ON clause
- WHERE - applies additional filters on the rows
- GROUP BY - groups the rows into groups by column values
- HAVING - filters groups
- ORDER BY - orders the remaining rows/groups
- LIMIT - filters on the remaining rows/groups
- SELECT - returns the selected columnd
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