Name: MySQL在10分鐘內（2020年）｜數據庫、SQL和MySQL的介紹。 (MySQL IN 10 MINUTES (2020) | Introduction to Databases, SQL, & MySQL)
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One thing you’ll notice when studying programming languages is that the concepts you encounter

This means focusing on a single topic can hardly deliver the content that must be explained

Despite that, we must start from somewhere, right?

My working experience tells me you will be much faster in learning and writing efficient

queries if you go through a brief introduction to databases.

It is the best thing to begin with, so here’s what I would like to share with you.

The table you see here contains data about the customer sales of a furniture store.

And, this is how we should read this information: Purchase number 1 was registered on the 3rd

Then, customer number 1 bought the item with code A 1.

Each of the four elements has a specific meaning.

A record is each entry that exists in a table.

Therefore, these four data values form one record, and these data values regarding purchase

You could use the terms row and record interchangeably.

Besides the rows, you can see the data is separated into four columns or fields.

A field is a column in a table containing specific information about every record in

This means all the records in a table, regardless if they are 10, 10 thousand, or 10 million,

will have a certain purchase number, date of purchase, customer ID, and item information.

When the data you have is organized into rows and columns, this means you are dealing with

This is important to mention, because you will often see in the literature that database

management relates to data stored in tabular form.

In this table, we know nothing about a customer besides her ID.

The information about customers is stored in another table, called “Customers”.

There are several fields, such as first and last names, e-mail addresses, and the number

of times customers have filed a complaint in our store.

So, what would the logic of that structure be?

Every time we have a customer with an ID number 1 in the “Sales” table, we can refer to

the customer with ID number 1 in the “Customers” table and see her name, email, and number

It contains the item code, product description, its unit price, ID, and name of the Company

that has delivered it, and the company’s headquarters phone number.

Here, the connection between the “Sales” table and the “Items” table is not the

Well, we could stuff this information into one table, and it would look like this.

I would not want to imagine what the table would look like if we had registered over

My point is – there are too many columns, and it is hard to understand what type of

information is contained in the larger table.

Relational algebra allows us to use mathematical logic and create a relation between a few

tables in a way that allows us to retrieve data efficiently.

Namely, these three tables – “Sales”, “Customers”, and “Items”– are related

through the customer ID or the “item code” columns and form a relational database.

And, importantly, each one bears a specific meaning and contains data characterizing it.

One of the tables contains information about sales, the other about customers, and the

To recap, remember the data values in a row form a record in a table, and each column

represents a field that carries specific information about every record.

A few related tables form a relational database.

And, for those of you who are interested in slightly more technical definitions, remember

the smallest unit that can contain a meaningful set of data is called an entity.

Therefore, the rows represent the horizontal entity in the table, the columns – its vertical

The table is a bigger data entity on its own.

It can also be referred to as a database object.

A single row of a table, being a single occurrence of that entity, can be also called an entity

We will gradually build the theoretical preparation you need before you begin coding.

Now that you know what a relational database is and have an idea about how it works, it

is much easier to understand how SQL fits the whole picture.

SQL is the programming language you need to execute commands that let you create and manipulate

We will not delve into strict and detailed technical definitions to explain how it works.

What you need to know is there are a few types of programming out there – procedural (imperative),

object-oriented, declarative, and functional.

Although with some procedural elements, SQL is mainly regarded as a declarative programming

This means, while coding, you will not be interested in how you want the job done.

The focus is on what result you want to obtain.

An abstract example would best clarify what we mean here.

When using a procedural language, such as C or Java, you must explicitly divide the

solution of a certain problem into several steps.

In a declarative language, this would sound like:

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MySQL在10分鐘內（2020年）｜數據庫、SQL和MySQL的介紹。 (MySQL IN 10 MINUTES (2020) | Introduction to Databases, SQL, & MySQL)

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