Aggregate Functions in SQL

Morteza Mousavi — Sat, 15 Feb 2025 06:02:16 +0000

Often, when querying in SQL, it is necessary to obtain the sum of a series of numbers, such as the total salary. In SQL, specific functions have been defined for this operation, known as Aggregate Functions or Grouping Functions.

Aggregate Functions are used for grouping when working with numerical and statistical data, allowing us to obtain results after performing a series of basic or advanced mathematical calculations.

Aggregate Functions are predefined functions that, when configured during a database query according to our needs, perform the desired operations and return the results.

Functions like Sum and Count are examples of Aggregate Functions, and their main characteristic is that they return a single value based on specific calculations on the values of a column.

Next, we will examine these functions.
Min Function

This function is used to obtain the minimum value from similar values.

SELECT MIN(grade)
FROM StudentGrade;

In the example above, we use this function to find the lowest score of students in the student grades table.
Max Function

This function is exactly the opposite of the Min function; it is used to find the maximum value among similar values.

SELECT MAX(salary)
FROM Personnel
WHERE Age < 35;

In this example, it finds and displays the highest salary among personnel who are under 35 years old.
Sum Function

This function is used to obtain the sum of numbers.

SELECT SUM(Salary)
FROM Personnel;

In this example, this function is used to sum all the salaries of the personnel in the personnel table.
Count Function

As the name of this function indicates, it is used to obtain the number of items.

SELECT COUNT(Id)
FROM Personnel;

The Count function is used to find the number of personnel.
Avg Function

The AVG function is actually an abbreviation for “average.” Using the AVG function, we can calculate and display the average of the desired values from grouped columns.

SELECT AVG(Salary)
FROM Personnel;

In this example, the AVG function is used to calculate the average salary of the personnel.

Building a Docker image from a JavaScript file

Morteza Mousavi — Sat, 08 Feb 2025 06:55:28 +0000

One of the simplest and most basic exercises in containerizing and getting familiar with Docker files is working with a simple JavaScript file. In this example, we will containerize a simple JavaScript file that doesn’t perform any specific function, or to put it more simply, we will create an image in Docker from this file.

To get started, we will create a JavaScript file that contains, for example, console.log('hello');.

Next, alongside this file, we will create a file named DockerFile. Make sure that the file name is exactly this, and then we will open the file to start our work.

First of all, we need Node.js to run JavaScript files, so we will download the Node.js image from Docker Hub:

`FROM node:alpine`

Using the FROM command, we download the Alpine version, which is a lightweight version of Node.js.

Now we need to create a directory in the image we are building to store the files and execute commands:

WORKDIR ./jsdir

With the WORKDIR command, you can create a directory with any name you want.

Now it’s time to copy the files into this directory:

`COPY hello.js .`

Now that we have copied the files, we move on to the step of executing the hello.js file that we created:

`CMD node hello.js`

Now, if you build and run the image using the following command, you will be able to see the printed output of “Hello”:

`docker build -t hello .`

DEV Community: Morteza Mousavi

Aggregate Functions in SQL

Building a Docker image from a JavaScript file