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Greatest N per group #25

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nickovchinnikov merged 1 commit into from
Sep 9, 2022
Merged

Greatest N per group #25

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20 changes: 20 additions & 0 deletions 5.MightySelect/7.Greatest_N_per_group.sql
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/* Last salary: greatest-n-per-group */

/* JOIN to subquery example */
SELECT e.emp_no, e.first_name, e.last_name, s2.salary, s2.to_date
FROM employees e
JOIN (
SELECT emp_no, MAX(to_date) as to_date FROM salaries GROUP BY emp_no
) s1
ON e.emp_no = s1.emp_no
JOIN salaries s2
ON s1.emp_no = s2.emp_no AND s1.to_date = s2.to_date;

/* Much more faster! */
SELECT e.emp_no, e.first_name, e.last_name, s1.salary, s1.to_date
FROM employees e
JOIN salaries s1
ON e.emp_no = s1.emp_no
LEFT JOIN salaries s2
ON e.emp_no = s2.emp_no AND s1.to_date < s2.to_date
WHERE s2.emp_no IS NULL;
5 changes: 5 additions & 0 deletions README.md
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Expand Up @@ -278,3 +278,8 @@ ___

### [Pull Request](https://github.com/nickovchinnikov/sql-box/pull/24)
___

### Greatest N per group

### [Pull Request](https://github.com/nickovchinnikov/sql-box/pull/25)
___