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Welcome to the world of Structured Query Language (SQL). The goal of this beginner’s guide is to help you understand SQL, a powerful language for interacting with databases. We will simplify the basics of SQL, demonstrating through examples how you can retrieve, insert, update, and delete data from a database.
What is SQL?
SQL (Structured Query Language) is a standard language for managing data held in a Relational Database Management System (RDBMS), or for stream processing in a Relational Data Stream Management System (RDSMS). SQL can be effectively used to insert, search, update, and delete database records. Not just that, but SQL can also perform functions such as managing, organizing, and manipulating the data in a database.
Creating a Table
One of the most important aspects of a database is its structure, defined by its tables. Let’s illustrate the SQL syntax for creating a table.
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CREATE TABLE Employees ( EmployeeID INT PRIMARY KEY, FirstName VARCHAR(100), LastName VARCHAR(100), Email VARCHAR(255), DOB DATE ); |
Inserting Data
We’ll now fill our ‘Employees’ table with some data. We need to mention the column names and the data that needs to be inserted.
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INSERT INTO Employees (EmployeeID, FirstName, LastName, Email, DOB) VALUES (1, 'John', 'Doe', <a href="mailto:'john.doe@example.com'" >'john.doe@example.com'</a>, '1980-01-01'); |
Retrieving Data
To retrieve the data from a database, we use the SELECT statement. For example, if we want to select all records from the ‘Employees’ table:
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SELECT * FROM Employees; |
Updating Data
The UPDATE SQL statement allows us to alter the data stored in our tables. Let’s say we want to change John Doe’s email:
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UPDATE Employees SET Email = <a href="mailto:'johndoe@example.com'" >'johndoe@example.com'</a> WHERE EmployeeID = 1; |
Deleting Data
If we ever need to remove a record from our table, SQL has the DELETE command. Let’s delete our previously created record for John Doe:
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DELETE FROM Employees WHERE EmployeeID = 1; |
There’s much more to SQL than what we’ve highlighted in this beginner’s guide. However, once you’ve mastered these basics, you’ll be well on your way to becoming proficient in SQL. Keep practicing, and happy querying!