SQL Exercises: Display distinct salesman and their cities
SQL UNION: Exercise-2 with Solution
2. From the following tables, write a SQL query to find distinct salespeople and their cities. Return salesperson ID and city.
Sample table: Salesman
Sample table: Customer
SELECT salesman_id, city FROM customer UNION (SELECT salesman_id, city FROM salesman)
salesman_id city 5001 New York 5002 London 5002 California 5006 Paris 5007 Rome 5002 Paris 5005 London 5003 Berlin 5007 Moscow 5003 San Jose
The said query in SQL that retrieves a list of unique pairs of salesman_id and city from two different tables, customer and salesman. The UNION operator is used to combine the results of two separate SELECT statements into a single result set.
The resulting table will contain all the unique combinations of salesman_id and city that appear in either the customer or salesman tables.
Relational Algebra Expression:
Relational Algebra Tree:
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Previous SQL Exercise: Display all salesmen and customer located in London.
Next SQL Exercise: Salesmen, customer involved in inventory management.
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SQL: Tips of the Day
Grouped LIMIT in PostgreSQL: Show the first N rows for each group?
db=# SELECT * FROM xxx; id | section_id | name ----+------------+------ 1 | 1 | A 2 | 1 | B 3 | 1 | C 4 | 1 | D 5 | 2 | E 6 | 2 | F 7 | 3 | G 8 | 2 | H (8 rows)
I need the first 2 rows (ordered by name) for each section_id, i.e. a result similar to:
id | section_id | name ----+------------+------ 1 | 1 | A 2 | 1 | B 5 | 2 | E 6 | 2 | F 7 | 3 | G (5 rows)
PostgreSQL v9.3 you can do a lateral join
select distinct t_outer.section_id, t_top.id, t_top.name from t t_outer join lateral ( select * from t t_inner where t_inner.section_id = t_outer.section_id order by t_inner.name limit 2 ) t_top on true order by t_outer.section_id;
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