SQL Exercise: Salesmen works either for one or more customer or not
SQL JOINS: Exercise-12 with Solution
Write a SQL statement to generate a list in ascending order of salespersons who work either for one or more customers or have not yet joined any of the customers.
Sample table: customer
Sample table: salesman
SELECT a.cust_name,a.city,a.grade, b.name AS "Salesman", b.city FROM customer a RIGHT OUTER JOIN salesman b ON b.salesman_id=a.salesman_id ORDER BY b.salesman_id;
Output of the Query:
cust_name city grade Salesman city Brad Davis New York 200 James Hoog New York Nick Rimando New York 100 James Hoog New York Graham Zusi California 200 Nail Knite Paris Julian Green London 300 Nail Knite Paris Geoff Cameron Berlin 100 Lauson Hen San Jose Brad Guzan London Pit Alex London Fabian Johnson Paris 300 Mc Lyon Paris Jozy Altidor Moscow 200 Paul Adam Rome
The said SQL query is performing a right outer join on the customer table alias a and the salesman table alias b on the 'salesman_id' column. It is then selecting the 'cust_name', 'city', and 'grade' columns from the customer table, and the 'name' and 'city' columns from the salesman table. The result is ordered by the 'salesman_id' column.
This query will select all the rows from the salesman table and any matching rows from the customer table and returning the results in the order of salesman_id. If there is no match, it will return NULL for the non-matching columns of customer table.
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Previous SQL Exercise: Find customers who have placed no order or one or more.
Next SQL Exercise: Salesmen who works either for one or more customer.
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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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