For an instructor lead, in-depth look at learning SQL click below.
Before proceeding to write and analyze SQL (Structured Query Language) code, it is important to have basic understanding of SQL. SQL is a programming language used to communicate with and manipulate databases. The majority of today’s relational database management systems (RDBMS) use SQL as their standard database language.
What is a Query?
A query is a question or a request. We use SQL, to communicate with a database for a specific purpose. Now, let’s move on to the ‘how’ part of using SQL Queries.
Writing a Basic SQL Query
A SQL query is composed using select statements which are used to fetch data from a database. Here is an example of a simple SQL ‘SELECT’ statement that retrieves all the data in the table:
|
1 2 3 |
SELECT * FROM Employees; |
This SQL statement selects all data from the ‘Employees’ table.
Selecting Specific Columns
If you want to fetch only specific columns, you can mention them in your SELECT statement like:
|
1 2 3 |
SELECT first_name, last_name FROM Employees; |
This statement will return only the ‘first_name’ and ‘last_name’ columns from the ‘Employees’ table.
Applying Conditions with ‘WHERE’ Clause
We can also filter records using the ‘WHERE’ clause. For instance, we can fetch details for employees whose age is above 35 like this:
|
1 2 3 |
SELECT * FROM Employees WHERE age > 35; |
Conclusion
SQL is a powerful language designed specifically for managing data held in Relational Database Management Systems. The possibilities with SQL queries are endless and range from fetching data, updating data, inserting data and deleting data. With this guide, you’ll be set to start your journey in building SQL queries!
Practice
The best way to learn SQL is through practice. Take these examples and modify the variables to suit your use case. With enough practice, you would be able to write SQL queries without any problems.