﻿ SQL: Highest grade for each of the cities of the customers

# SQL Exercises: Highest grade for each of the cities of the customers

## SQL Aggregate Functions: Exercise-8 with Solution

From the following table, write a SQL query to find the highest grade of the customers in each city. Return city, maximum grade.

Sample table: customer

``` customer_id |   cust_name    |    city    | grade | salesman_id
-------------+----------------+------------+-------+-------------
3002 | Nick Rimando   | New York   |   100 |        5001
3007 | Brad Davis     | New York   |   200 |        5001
3005 | Graham Zusi    | California |   200 |        5002
3008 | Julian Green   | London     |   300 |        5002
3004 | Fabian Johnson | Paris      |   300 |        5006
3009 | Geoff Cameron  | Berlin     |   100 |        5003
3003 | Jozy Altidor   | Moscow     |   200 |        5007
3001 | Brad Guzan     | London     |       |        5005
```

Sample Solution:

``````-- This query retrieves the maximum 'grade' value for each 'city' from the 'customer' table.
-- Specifies the table from which to retrieve the data (in this case, 'customer').
FROM customer
-- Groups the result set by the 'city' column.
GROUP BY city;
``````

Output of the Query:

```city		max
London		300
Paris		300
New York	200
California	200
Berlin		100
Moscow		200
```

Explanation Code

The said SQL statement retrieves the maximum "grade" value for each "city" in the 'customer' table. A "GROUP BY" clause is used in the query to group the 'customer' table according to a city, and a "MAX" function is used to determine the maximum grade for each group based on the "GROUP BY" clause.

Relational Algebra Expression:

Relational Algebra Tree:

Explanation:

Visual presentation :

## Query Visualization:

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Previous SQL Exercise: Find the minimum purchase amount of all the orders.
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