PostgreSQL ROLLUP is a sub-clause of the GROUP BY clause that generates a result set which shows the aggregate for the hierarchy of values in the selected columns. It allows multiple groupings set the same as CUBE sub-clause, but there is only one difference between CUBE and ROLLUP.
CUBE sub-clause generates a result set that shows aggregate for all combinations of values in the selected columns
ROLLUP is a sub-clause of the GROUP BY clause that generates a result set which shows the aggregate for the hierarchy of values in the selected columns.
CUBE(Col_1, Col_2, Col_3) --------------------------------- Col_1, Col_2, Col_3 Col_1, Col_2 Col_1, Col_3 Col_1 Col_2,Col_3 Col_2 Col_3 () |
ROLLUP(Col_1, Col_2, Col_3) --------------------------------- Col_1, Col_2, Col_3 Col_1, Col_2 Col_1 () |
Syntax of the ROLLUP sub-clause:
SELECT c1, c2, c3, aggregate (c4) FROM table_name GROUP BY ROLLUP (c1, c2, c3); |
Query is same as GROUP BY except added a new ROLLUP sub-clause after GROUP BY clause.
We can understand the use of ROLLUP sub-clause by example.
Suppose we have a PRODUCTS table with columns like product name, category, quantity, etc.
CREATE TABLE products ( product_id serial NOT NULL, product_name text, category text, quantity numeric ); -- Inserted some records into PRODUCTS table INSERT INTO products(product_name, category, quantity) VALUES('prod_1','category_1',100); INSERT INTO products(product_name, category, quantity) VALUES('prod_2','category_2',200); INSERT INTO products(product_name, category, quantity) VALUES('prod_3','category_3',400); INSERT INTO products(product_name, category, quantity) VALUES('prod_4','category_4',500); |
CUBE sub-clause by example
SELECT product_name, category, SUM(quantity) FROM products GROUP BY ROLLUP (product_name,category) ORDER BY product_name, category; |
Result:
