﻿ SQL: Find number of customers have listed their names

# SQL Exercises: Find number of customers have listed their names

## SQL Aggregate Functions: Exercise-4 with Solution

From the following table, write a SQL query to count the number of customers. Return number of customers.

Sample table: customer

Sample Solution:

``````SELECT COUNT(*)
FROM customer;
``````

Output of the Query:

```count
8
```

Code Explanation:

The said SQL query that retrieve the total number of rows in the 'customer' table. The "SELECT COUNT(*)" statement specifies that the number of rows in the table should be counted. The "(*)" is a wildcard that counts all rows, regardless of the specific columns and their values.
The result of this query will be a single value that represents the total number of rows in the 'customer' table.

Relational Algebra Expression:

Relational Algebra Tree:

Explanation:

Visual presentation:

## Query Visualization:

Duration:

Rows:

Cost:

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Previous SQL Exercise:Find the number of salesmen for each customer.
Next SQL Exercise: How many customers get a grade for their performance.

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## SQL: Tips of the Day

What is the best way to paginate results in SQL Server?

```SELECT  *
FROM    ( SELECT    ROW_NUMBER() OVER ( ORDER BY OrderDate ) AS RowNum, *
FROM      Orders
WHERE     OrderDate >= '1980-01-01'
) AS RowConstrainedResult
WHERE   RowNum >= 1
AND RowNum < 20
ORDER BY RowNum
```

Database: SQL Server

Ref: https://bit.ly/3MGrNlk

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