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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 Expression: Find number of customers have listed their names.

Relational Algebra Tree:

Relational Algebra Tree: Find number of customers have listed their names.

Explanation:

Syntax of find number of customers have listed their names

Visual presentation:

Find number of customers have listed their names

Practice Online


Query Visualization:

Duration:

Query visualization of Find number of customers have listed their names - Duration

Rows:

Query visualization of Find number of customers have listed their names - Rows

Cost:

Query visualization of Find number of customers have listed their names - 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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