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Structured Query Language, commonly known as SQL, is a powerful language used to interact with databases. Its main purpose is to retrieve, update, or manipulate data within a database. This guide will take you through the basics of learning SQL, allowing you to get started from scratch.
Introduction to SQL
SQL is widely used because of its simplicity, straightforward syntax and massive potential in handling structured data. It operates via intuitive, declarative statements. For instance, to fetch all data from a table named ‘Employees’, we simply write:
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SELECT * FROM Employees |
Basic SQL Commands
SELECT
The SELECT statement is used to fetch data from a database. It allows you to specify the data you want. For example, to select only the ‘Name’ and ‘Job’ columns from the ‘Employees’ table:
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SELECT Name, Job FROM Employees |
WHERE
The WHERE clause is used to filter records. This command fetches data under certain conditions. If you want to fetch employee data where the ‘Job’ is ‘Engineer’:
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SELECT * FROM Employees WHERE Job = 'Engineer' |
INSERT INTO
This command is used to insert new data into a database. For example, to add new employee data into the ‘Employees’ table:
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INSERT INTO Employees (Name, Job) VALUES ('Mark', 'Engineer') |
UPDATE
The UPDATE command modifies existing data within a table. If Mark got a promotion and his job title changed, we could update his record:
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UPDATE Employees SET Job = 'Senior Engineer' WHERE Name = 'Mark' |
DELETE
The DELETE command removes existing data from a table. If an employee, say John, leaves the company, you can remove his record:
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DELETE FROM Employees WHERE Name = 'John' |
Conclusion
SQL is a must-have tool in your programming arsenal, especially when working with data. By mastering the basic commands outlined above, you can query databases with confidence. Remember, practice makes perfect. So, keep coding and exploring new SQL techniques!