Analytic Functions – Aggregations

Private: Mastering SQL using Postgresql Writing Advanced SQL Queries Analytic Functions – Aggregations

Let us see how we can perform aggregations with in a partition or group using Windowing/Analytics Functions.

For simple aggregations where we have to get grouping key and aggregated results we can use GROUP BY.
If we want to get the raw data along with aggregated results, then using GROUP BY is not possible or overly complicated.
Using aggregate functions with OVER Clause not only simplifies the process of writing query, but also better with respect to performance.
Let us take an example of getting employee salary percentage when compared to department salary expense.

Warning

If you are using Jupyter based environment make sure to restart the kernel, as the session might have been already connected with retail database.

%load_ext sql

%env DATABASE_URL=postgresql://itversity_hr_user:hr_password@localhost:5432/itversity_hr_db

env: DATABASE_URL=postgresql://itversity_hr_user:hr_password@localhost:5432/itversity_hr_db

%%sql

SELECT employee_id, department_id, salary 
FROM employees 
ORDER BY department_id, salary
LIMIT 10

10 rows affected.

employee_id	department_id	salary
200	10	4400.00
202	20	6000.00
201	20	13000.00
119	30	2500.00
118	30	2600.00
117	30	2800.00
116	30	2900.00
115	30	3100.00
114	30	11000.00
203	40	6500.00

Note

Let us write the query using GROUP BY approach.

%%sql

SELECT department_id,
    sum(salary) AS department_salary_expense
FROM employees
GROUP BY department_id
ORDER BY department_id

 * postgresql://itversity_hr_user:***@localhost:5432/itversity_hr_db
12 rows affected.

department_id	department_salary_expense
10	4400.00
20	19000.00
30	24900.00
40	6500.00
50	156400.00
60	28800.00
70	10000.00
80	304500.00
90	58000.00
100	51600.00
110	20300.00
None	7000.00

%%sql

SELECT e.employee_id, e.department_id, e.salary,
    ae.department_salary_expense,
    ae.avg_salary_expense
FROM employees e JOIN (
    SELECT department_id, 
        sum(salary) AS department_salary_expense,
        round(avg(salary)::numeric, 2) AS avg_salary_expense
    FROM employees
    GROUP BY department_id
) ae
ON e.department_id = ae.department_id
ORDER BY department_id, salary
LIMIT 10

 * postgresql://itversity_hr_user:***@localhost:5432/itversity_hr_db
10 rows affected.

employee_id	department_id	salary	department_salary_expense	avg_salary_expense
200	10	4400.00	4400.00	4400.00
202	20	6000.00	19000.00	9500.00
201	20	13000.00	19000.00	9500.00
119	30	2500.00	24900.00	4150.00
118	30	2600.00	24900.00	4150.00
117	30	2800.00	24900.00	4150.00
116	30	2900.00	24900.00	4150.00
115	30	3100.00	24900.00	4150.00
114	30	11000.00	24900.00	4150.00
203	40	6500.00	6500.00	6500.00

%%sql

SELECT e.employee_id, e.department_id, e.salary,
    ae.department_salary_expense,
    ae.avg_salary_expense,
    round(e.salary/ae.department_salary_expense * 100, 2) pct_salary
FROM employees e JOIN (
    SELECT department_id, 
        sum(salary) AS department_salary_expense,
        round(avg(salary)::numeric, 2) AS avg_salary_expense
    FROM employees
    GROUP BY department_id
) ae
ON e.department_id = ae.department_id
ORDER BY department_id, salary
LIMIT 10

 * postgresql://itversity_hr_user:***@localhost:5432/itversity_hr_db
10 rows affected.

employee_id	department_id	salary	department_salary_expense	avg_salary_expense	pct_salary
200	10	4400.00	4400.00	4400.00	100.00
202	20	6000.00	19000.00	9500.00	31.58
201	20	13000.00	19000.00	9500.00	68.42
119	30	2500.00	24900.00	4150.00	10.04
118	30	2600.00	24900.00	4150.00	10.44
117	30	2800.00	24900.00	4150.00	11.24
116	30	2900.00	24900.00	4150.00	11.65
115	30	3100.00	24900.00	4150.00	12.45
114	30	11000.00	24900.00	4150.00	44.18
203	40	6500.00	6500.00	6500.00	100.00

Note

Let us see how we can get it using Analytics/Windowing Functions.

We can use all standard aggregate functions such as count, sum, min, max, avg etc.

%%sql

SELECT e.employee_id, e.department_id, e.salary,
    sum(e.salary) OVER (
        PARTITION BY e.department_id
    ) AS department_salary_expense
FROM employees e
ORDER BY e.department_id
LIMIT 10

 * postgresql://itversity_hr_user:***@localhost:5432/itversity_hr_db
10 rows affected.

employee_id	department_id	salary	department_salary_expense
200	10	4400.00	4400.00
201	20	13000.00	19000.00
202	20	6000.00	19000.00
114	30	11000.00	24900.00
115	30	3100.00	24900.00
116	30	2900.00	24900.00
117	30	2800.00	24900.00
118	30	2600.00	24900.00
119	30	2500.00	24900.00
203	40	6500.00	6500.00

%%sql

SELECT e.employee_id, e.department_id, e.salary,
    sum(e.salary) OVER (
        PARTITION BY e.department_id
    ) AS department_salary_expense,
    round(e.salary / sum(e.salary) OVER (
        PARTITION BY e.department_id
    ) * 100, 2) AS pct_salary
FROM employees e
ORDER BY e.department_id,
    e.salary
LIMIT 10

 * postgresql://itversity_hr_user:***@localhost:5432/itversity_hr_db
10 rows affected.

employee_id	department_id	salary	department_salary_expense	pct_salary
200	10	4400.00	4400.00	100.00
202	20	6000.00	19000.00	31.58
201	20	13000.00	19000.00	68.42
119	30	2500.00	24900.00	10.04
118	30	2600.00	24900.00	10.44
117	30	2800.00	24900.00	11.24
116	30	2900.00	24900.00	11.65
115	30	3100.00	24900.00	12.45
114	30	11000.00	24900.00	44.18
203	40	6500.00	6500.00	100.00

%%sql

SELECT e.employee_id, e.department_id, e.salary,
    sum(e.salary) OVER (
        PARTITION BY e.department_id
    ) AS sum_sal_expense,
    round(avg(e.salary) OVER (
        PARTITION BY e.department_id
    ), 2) AS avg_sal_expense,
    min(e.salary) OVER (
        PARTITION BY e.department_id
    ) AS min_sal_expense,
    max(e.salary) OVER (
        PARTITION BY e.department_id
    ) AS max_sal_expense,
    count(e.salary) OVER (
        PARTITION BY e.department_id
    ) AS cnt_sal_expense
FROM employees e
ORDER BY e.department_id,
    e.salary
LIMIT 10

 * postgresql://itversity_hr_user:***@localhost:5432/itversity_hr_db
10 rows affected.

employee_id	department_id	salary	sum_sal_expense	avg_sal_expense	min_sal_expense	max_sal_expense	cnt_sal_expense
200	10	4400.00	4400.00	4400.00	4400.00	4400.00	1
202	20	6000.00	19000.00	9500.00	6000.00	13000.00	2
201	20	13000.00	19000.00	9500.00	6000.00	13000.00	2
119	30	2500.00	24900.00	4150.00	2500.00	11000.00	6
118	30	2600.00	24900.00	4150.00	2500.00	11000.00	6
117	30	2800.00	24900.00	4150.00	2500.00	11000.00	6
116	30	2900.00	24900.00	4150.00	2500.00	11000.00	6
115	30	3100.00	24900.00	4150.00	2500.00	11000.00	6
114	30	11000.00	24900.00	4150.00	2500.00	11000.00	6
203	40	6500.00	6500.00	6500.00	6500.00	6500.00	1

Warning

If you are using Jupyter based environment make sure to restart the kernel, as the session might have been already connected with hr database.

%load_ext sql

%env DATABASE_URL=postgresql://itversity_retail_user:retail_password@localhost:5432/itversity_retail_db

env: DATABASE_URL=postgresql://itversity_retail_user:retail_password@localhost:5432/itversity_retail_db

%%sql

SELECT
    order_date,
    order_item_product_id,
    revenue,
    sum(revenue) OVER (PARTITION BY order_date) AS sum_revenue,
    min(revenue) OVER (PARTITION BY order_date) AS min_revenue,
    max(revenue) OVER (PARTITION BY order_date) AS max_revenue
FROM daily_product_revenue
ORDER BY order_date,
    revenue DESC
LIMIT 10

10 rows affected.

order_date	order_item_product_id	revenue	sum_revenue	min_revenue	max_revenue
2013-07-25 00:00:00	1004	5599.72	31547.23	49.98	5599.72
2013-07-25 00:00:00	191	5099.49	31547.23	49.98	5599.72
2013-07-25 00:00:00	957	4499.70	31547.23	49.98	5599.72
2013-07-25 00:00:00	365	3359.44	31547.23	49.98	5599.72
2013-07-25 00:00:00	1073	2999.85	31547.23	49.98	5599.72
2013-07-25 00:00:00	1014	2798.88	31547.23	49.98	5599.72
2013-07-25 00:00:00	403	1949.85	31547.23	49.98	5599.72
2013-07-25 00:00:00	502	1650.00	31547.23	49.98	5599.72
2013-07-25 00:00:00	627	1079.73	31547.23	49.98	5599.72
2013-07-25 00:00:00	226	599.99	31547.23	49.98	5599.72

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