﻿ SQL: How many customers get a grade for their performance

# SQL Exercises: How many customers get a grade for their performance

## SQL Aggregate Functions: Exercise-5 with Solution

From the following table, write a SQL query to determine the number of customers who received at least one grade for their activity.

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 counts the total number of rows where the 'grade' column is not NULL in the 'customer' table.
-- Specifies the table from which to retrieve the data (in this case, 'customer').
FROM customer;
``````

Output of the Query:

```count
7
```

Code Explanation:

The said SQL statement is used to count the total number of grades present in the 'customer' table. The "COUNT" function is used to count the number of non-null values in the specified column, in this case, the "grade" column.
The "ALL" keyword is not necessary as it is the default behavior for the "COUNT" function to count all values, including duplicates.

Explanation:

visual presentation:

## Query Visualization:

Duration:

Rows:

Cost:

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Previous SQL Exercise: Find number of customers have listed their names.
Next SQL Exercise: Find the maximum purchase amount of all the orders.

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