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Welcome to this introductory guide on understanding data retrieval using SQL. SQL, which stands for Structured Query Language, is a programming language that’s used to communicate with and manipulate databases. The focus of this blog will be on SQL as a tool for data retrieval.
What is SQL?
SQL is a language which is used to interact and communicate with databases. It consists of a data definition language, data manipulation language, and data control language. For today, we will be focusing on the Data Manipulation Language (DML) aspect of SQL, which includes the SELECT, INSERT, UPDATE, and DELETE commands.
SQL SELECT Command
The SELECT command is the cornerstone of SQL. As the name implies, it’s used to select data from databases. The simplest example of a SELECT statement is as follows:
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SELECT * FROM Customers; |
In this example, the * character is a wildcard that signifies “all”. The command above will return all data from the Customers table.
Selecting Specific Columns
What if you don’t want to retrieve all columns from the table but only specific ones? You can mention the specific column names separated by commas. Let’s say we only want the “Name” and “Email” columns from the “Customers” table. You will write:
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SELECT Name, Email FROM Customers; |
WHERE Clause
When you want to filter the result set based on specific conditions, SQL provides the WHERE clause. Consider it as a screening criteria. For example, let’s say you want to select only the customers who live in the city of “New York”. You would write this as:
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SELECT * FROM Customers WHERE City ='New York'; |
Sorting The Result Set
SQL provides the ORDER BY clause to sort your result set. You can sort the data in ascending order (ASC) or in descending order (DESC). For instance, if we want to sort our customers based on their names in alphabetical order, we will write:
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SELECT * FROM Customers ORDER BY Name ASC; |
Today we’ve overviewed the basics of data retrieval using SQL. There’s a lot more to SQL data retrieval that can make your SQL queries faster and your life easier, but it all begins with these basics. Next time, we will discuss joining tables, grouping, and more advanced SQL functions. Until then, happy coding!