For an instructor lead, in-depth look at learning SQL click below.
Structured Query Language, commonly known as SQL, is a standardized programming language used for managing and manipulating databases. At its core, SQL is used for communicating with databases, and it allows you to access and extract valuable information. This article aims to break-down the primary SQL queries you’ll need to get started.
Getting Started with SQL
Generally, when you’re working with SQL, you’re working with relational databases. These databases are structured like a grid with columns (fields) and rows (records). To understand how SQL works, let’s use an example database table of ‘Pets’, with columns for ‘PetID’, ‘PetName’, ‘Breed’, and ‘Owner’.
SELECT
One of the most basic queries in SQL is SELECT. It is used to select data from a database and retrieve just the information you want. For example:
|
1 2 3 |
SELECT PetName, Breed FROM Pets; |
This SQL statement SELECTs the ‘PetName’ and ‘Breed’ from the ‘Pets’ table and displays them.
WHERE
The WHERE clause in SQL is used to filter records. If you want to select specific records that fulfill a particular condition, you’d use WHERE. For instance:
|
1 2 3 |
SELECT * FROM Pets WHERE Owner='John'; |
This SQL statement SELECTs all records from the ‘Pets’ table where the ‘Owner’ is ‘John’.
UPDATE
UPDATE SQL command is used to modify existing records in a table. You can update single or multiple records using this command. Here’s an example:
|
1 2 3 |
UPDATE Pets SET Owner='Jane' WHERE PetName='Toby'; |
This SQL statement will UPDATE the ‘Pets’ table, changing ‘Owner’ to ‘Jane’ where ‘PetName’ is ‘Toby’.
DELETE
The DELETE statement in SQL is used to delete existing records in a table. Similar to the UPDATE command, the DELETE command should be used with caution as it removes records permanently. Here’s how you can use it:
|
1 2 3 |
DELETE FROM Pets WHERE PetID=7; |
This SQL statement will DELETE the record from the ‘Pets’ table where ‘PetID’ is 7. Be careful with this query, as once the data is deleted, it can’t be recovered.
Conclusion
In conclusion, SQL is a powerful tool for manipulating and retrieving data stored in relational databases. Even though it requires a unique way of thinking, once mastered, it provides great flexibility in how you interact with stored information.