For an instructor lead, in-depth look at learning SQL click below.
Structured Query Language (SQL) is a powerful tool that allows you to interact with databases. Regardless of your profession, understanding SQL can greatly leverage your ability to handle data. This guide aims to help beginners become confidant in writing SQL.
What is SQL?
SQL is a standard language designed for managing data held in a relational database management system (RDBMS). In simpler terms, it’s a tool that lets you “talk” to databases to view, manipulate, and manage their data, and it is widely used among businesses and software applications.
SQL Structure
The SQL language is vast, but can be broken down into a few key categories:
- Data Query Language (DQL): This includes the SELECT statement that allows you to query data.
- Data Manipulation Language (DML): This consists of commands like INSERT, UPDATE, and DELETE. As the name suggests, these are used to manipulate data within tables.
- Data Definition Language (DDL): DDL commands, such as CREATE, ALTER, and DROP, are used for defining and modifying database schema.
- Data Control Language (DCL): GRANT and REVOKE commands are parts of DCL, and they’re used to control the access to the database.
SQL in Action
1. Data Retrieval with SELECT
One of the most common tasks you’ll perform with SQL is querying data. The SELECT command is used to do this. Let’s look at an example:
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SELECT * FROM Orders; |
This SQL statement selects all data from the “Orders” table.
2. Adding Records with INSERT
To add new records to a database table, we use the INSERT command. Below is an example:
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INSERT INTO Customers (CustomerName, ContactName, Country) VALUES ('Cardinal', 'Tom B. Erichsen', 'Norway'); |
This SQL statement inserts a new record into the “Customers” table. The new record includes customer name, contact name, and country.
3. Updating Records with UPDATE
The UPDATE command allows you to modify existing records. Here’s how to use it:
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UPDATE Customers SET ContactName = 'Alfred Schmidt', City= 'Frankfurt' WHERE CustomerID = 1; |
This SQL statement updates the record in the ‘Customers’ table where ‘CustomerID’ equals 1, setting a new contact name and city.
4. Deleting Records with DELETE
The DELETE command removes records. Let’s delete a record from the “Customers” table:
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DELETE FROM Customers WHERE CustomerName='Alfreds'; |
With this statement, we delete the ‘Alfreds’ record from the ‘Customers’ table.
To Conclude
SQL is a powerful language with a wide range of capabilities for database management. The more you practice, the better you’ll get. Happy querying!