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  • I

  • am sure you are now keen to begin to use this software to organize and manipulate data in

  • practice.

  • Let’s start by creating a database.

  • We will use theSalesdatabase.

  • We will show you how to create your own database, also called schema, starting from scratch.

  • Only in this way can you grasp just how powerful SQL can be.

  • Therefore, first we will define a database, and then create the other components, such

  • as tables and fields.

  • We will use the Data Definition Language CREATE statement to create a database.

  • Quite intuitively, the command we need in this case is CREATE DATABASE.

  • The syntax to abide by is CREATE DATABASE, the optional statement [IF NOT EXISTS], the

  • name of the database, and finally, a semicolon.

  • Let’s break down this entire line to understand the meaning of each element.

  • CREATE DATABASE will obviously create a database as an abstract unit.

  • This means that for the moment the database will not contain any data and will simply

  • represent an object ready to be filled with information.

  • Think of it as creating a canvas on which you would be able to draw your relational

  • schemas later.

  • IF NOT EXISTS will verify if a database with the same name exists already.

  • If it does, this will impede us from creating a database with the same name.

  • The brackets around indicate that the statement between them is optional in the syntax.

  • Optional means you could either type or omit the statement.

  • This is the situation with [IF NOT EXISTS] – even if you don’t include it the code

  • will run anyway.

  • Nevertheless, we advise you to always use it because it allows you to avoid potential

  • errors when working with large amounts of data.

  • It is good to build the habit of attaching this phrase straight after the CREATE statement.

  • Next, we will have to specify the name of the new database.

  • We strongly suggest you give a name that is short but at the same time as related to the

  • content of the data as possible.

  • Try to avoid assigning names likedatabase_01” ordatabase_about_sales_in_New_York”.

  • In our case, the data we will work with is about the customer sales registered in a company.

  • For this reason, we will call the databaseSales”.

  • Whether you use uppercase or lowercase letters only, or bothit’s the same for SQL.

  • The SQL code is not case sensitive neither when assigning names of objects nor when writing

  • queries.

  • Otherwise, in this element the quotes are optionalyou could either saySales

  • within quotes, or without using any quotes.

  • It makes no difference.

  • Finally, you should always end your statements with the semicolon character.

  • It functions as a statement terminator.

  • Yes, it is often true that your queries will run properly without it, but this is not the

  • point.

  • In longer scripts, when your code contains more than a single statement, the semicolon

  • is indispensable.

  • So, please, try to end your statements with this characterthis will not only help

  • you avoid errors sometimes, but will also improve the readability of your code.

  • Ok!

  • So

  • I guess we are ready to type down our first query and run it, aren’t we?

  • Let’s type CREATE DATABASE IF NOT EXISTS, without brackets, “Sales” (keeping in

  • mind that we are allowed to omit the quotes without any problem), and semicolon.

  • Now, it is important to note that this entire line is nothing but a piece of text until

  • you execute it.

  • To execute, or run, a query, you must press this lightning symbol.

  • The alternative is to implement the shortcut combination Ctrl, Shift and Enter.

  • So, what are we waiting for?

  • Let’s press this button and see the output of our work.

  • At first sight, it seems nothing happened.

  • This is not true though.

  • When new databases, schemas, or tables are created, we always need to refresh the content

  • in theSchemassection at the bottom left part of the screen by pressing this little

  • button here.

  • Ha!

  • TheSalesdatabase is ready for use!

  • Great!

  • Please, remember that you could have achieved the same output if you had used CREATE SCHEMA

  • instead of CREATE DATABASE.

  • Considering that database and schema are practically synonyms, this seems like a logical alternative,

  • right?

  • Well, we just completed our first taskcreating a database.

  • Congratulations!

  • In this video, we will look at the MySQL workbench interface in more detail as it can help us

  • manage our database better.

  • The symbol located before the nameSalesindicates us that the object in question is

  • a database.

  • Youve seen it before, haven’t you?

  • ? It stands for a database.

  • Moreover, by pressing this miniature triangle, we see how this database can be broken down

  • into four componentsTables, Views, Stored Procedures, and Functions.

  • Since we have not created any of these for the moment, nothing will happen if you click

  • any of the respective names.

  • It is important to be familiar with this little symbol that appears when you hover above the

  • name of the database.

  • It is a feature of the MySQL workbench you will love when you fill in your database with

  • data.

  • Once you press it, a new tab containing information about the database will open in the right

  • part of the screen.

  • Although all these fields are currently empty, when we fill our database with information,

  • we will be able to inspect its tables, columns, indexes, triggers, views, stored procedures,

  • functions, and grants in a great level of detail.

  • All right.

  • We just saw how to obtain information about theSalesdatabase and some of its components.

  • However, we don’t know how to tell the computer thatSalesis going to be the database

  • we want to apply the SQL code and operations to.

  • After having created the database, you must typeUSESalessemicolonin the

  • SQL query editor field.

  • By running this line, you will select the existingSalesdatabase and you will

  • be ready to apply various SQL commands and data manipulation tasks on it.

I

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學習如何創建數據庫|SQL教程的第一步 (Learn How to Create a Database | First Steps in SQL Tutorial)

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    林宜悉 發佈於 2021 年 01 月 14 日
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