For an instructor lead, in-depth look at learning SQL click below.
Just as a solid building starts with a strong foundation, so too does the journey into SQL— a standardized programming language designed to manage, manipulate, and retrieve data stored in relational databases. The following guide will give you a gentle introduction to SQL and help you lay a firm foundation for your future learning.
Introduction to SQL
SQL, or Structured Query Language, is a language designed specifically for communicating with databases. SQL is essentially the backbone of any software that needs to store or retrieve data.
A Simple SQL Query
To illustrate, let’s consider an imaginary database table called “employees”. Each row of the table represents a different employee, and the columns contain attributes of the employees, such as employee_id, first_name, last_name, department, and salary. The following SQL statement retrieves the entire data from the “employees” table:
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SELECT * FROM employees; |
Breaking down the query
The SELECT statement is used to select data from a database. The asterisk (*) is used to select all columns in the table. The ‘FROM’ keyword specifies which table to select or delete data from.
Focused Retrievals with SQL
In many scenarios, you may be interested in a subset of the data. For example, you might want to retrieve data about employees only from a certain department or those with a salary above a certain value. Here’s how you can do it:
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SELECT * FROM employees WHERE department = 'sales'; SELECT * FROM employees WHERE salary > 50000; |
What do these queries do?
The WHERE keyword allows you to filter the resulting data based on specified conditions. In the first example, we’re retrieving data about employees belonging to the sales department. In the second example, we’re retrieving data about employees with a salary greater than 50000.
Winding Up
To wrap up, SQL is a powerful tool for pulling precise information from a database. Getting the hang of basic SQL statements puts you one step closer to harnessing the power of your data. By learning how to use ‘SELECT’ and ‘FROM’, and coupling these commands with ‘WHERE’ statements, you’ll soon be able to construct useful queries for your specific data needs.