Bài 1 – SQL Constraint NOT NULL và UNIQUE | sql is not null

Bài 1 – SQL Constraint NOT NULL và UNIQUE

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นอกจากการดูบทความนี้แล้ว คุณยังสามารถดูข้อมูลที่เป็นประโยชน์อื่นๆ อีกมากมายที่เราให้ไว้ที่นี่: ดูความรู้เพิ่มเติมที่นี่

Constraints là các ràng buộc dữ liệu trong các cột của Bảng. Người thiết kế phải nắm rõ để làm khi thiết kế CSDL. Trong bài này chúng ta học về 2 constraint quan trọng là NOT NULL và UNIQUE.

Oracle – SQL – Not Null Constraint

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Oracle SQL Not Null Constraint
Watch more Videos at https://www.tutorialspoint.com/videotutorials/index.htm
Lecture By: Mr. Anadi Sharma, Tutorials Point India Private Limited.

Should I Learn SQL or Access?

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Should I learn SQL or Access?
SQL is free.
Sometimes you get what you pay for. And sometimes what matters is what you can get out of it.
SQL does not have data extraction. However, SQL express has an import and export wizard.
Why do people promote Microsoft Access for data analytics?
Microsoft Access is cheaper than SAS and does just as good a job at midlevel analysis. You get a miniversion of Big Data without spending 20K per license.
And you can import and export to Microsoft Excel.
There are tools for exporting SQL database entries to Excel, too.
I think everything is plug and play with Excel.
That’s what you get when you have the 800 pound gorilla on the computing block. If you learn Microsoft Access, you’ll be learning a tool installed on 80% of all computers.
And a lot of hiring managers have heard of it if only because they’ve seen it above Microsoft Excel and Word. So why would I want to learn SQL?
SQL is a key tool in manipulating and maintaining databases. These are databases larger and more complex than anything you can run in Access.
Why do so many people hate SQL?
SQL was designed before object oriented programming and web apps. And then there’s the fact that its queries are more like SAS than Python or Java programming, throwing a lot of programmers in for a loop.
That does not tell me why I should learn it.
If you want to maintain databases, it is either SQL or Oracle. And since Oracle is so darn expensive, SQL it is for many midsized companies and even large ones.
There’s NoSQL. It is like the uncola of databases.
NoSQL does not have a standard engine or toolset. It has to grow up before it can be considered a proper rival to SQL.
So if I want to manage and query databases, it is SQL.
Unless you want to be a glorified Microsoft Office expert, yeah.

SQL with Microsoft Access 2016 lesson 2 – Inserting records

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In this video we cover the Insert Into SQL statement to insert some data into a table. We ran into some problems already some phone numbers got stripped off a zero at the front, and it accepted some numbers with incorrect number of digits. All these will be fixed in the next tutorial.

[SQL SEVER TỪ A-Z] Bài 18: Null, Not Null, Isnull

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