2023 SQL Cheat Sheet for IQCode Users
Introduction: What is SQL?
In order to understand SQL, we first need to understand databases and database management systems (DBMS), which is a collection of tools designed to manipulate, organize and visualize data within a database. Data is essentially a collection of facts related to a particular object, and a database is a collection of these small units of data, organized systematically. Specifically, a relational database management system (RDBMS) follows standard rules that facilitate quick responses between the database and the user.
Once we have a basic understanding of DBMS and RDBMS, we can then move on to understanding SQL, otherwise known as Structured Query Language. SQL is the language used by users to interact with databases, allowing us to store, manipulate, and retrieve data from the database.
SQL allows users to interact with databases and manipulate the data within them. With SQL, we can create databases and add data to them in the form of tables. Some common functionalities that can be performed using SQL on a database include:
- Create or delete a database
- Create, alter, or delete tables within a database
- Select data from tables
- Insert data into tables
- Update data in tables
- Delete data from tables
- Create views within the database
- Execute various aggregate functions
Learn SQL: Basic to Advanced Concepts
To begin your journey of learning SQL, the first step is to install it on your system.
Step 1: Download and Install MySQL
Go to the official website of MySQL and download the latest version:
Then follow the installation instructions for your specific operating system.
Step 2: Verify Installation
To verify that MySQL has been installed correctly, open the terminal and enter the following command:
If MySQL has been installed properly, you should see the version number displayed in the terminal.
Step 3: Connect to MySQL Server
Now that MySQL is installed, you can connect to the MySQL server using the following command:
mysql -u username -p
Replace 'username' with the name of your user account and enter your password when prompted.
Step 4: Start Using SQL
You can now start using SQL by entering commands into the MySQL prompt. For example, to create a new database, you can use the following command:
CREATE DATABASE mydatabase;
This will create a new database called 'mydatabase'.
Performing CRUD Operations in SQL
CRUD operations refer to Create, Read, Update, and Delete operations in a database. Here's an example of how you can perform these operations in SQL.
Create: To create a new record in a database table, use the INSERT statement. For example:
INSERT INTO users (name, age, email) VALUES ('John Doe', 25, '[email protected]');
This will create a new user with the name 'John Doe', age of 25, and email of '[email protected]'.
Read: To retrieve data from a table, use the SELECT statement. For example:
SELECT * FROM users;
This will retrieve all data from the 'users' table.
Update: To update an existing record in a table, use the UPDATE statement. For example:
UPDATE users SET age = 30 WHERE name = 'John Doe';
This will update the age of the user with the name 'John Doe' to 30.
Delete: To delete a record from a table, use the DELETE statement. For example:
DELETE FROM users WHERE name = 'John Doe';
This will delete the user with the name 'John Doe' from the 'users' table.
Important SQL Keywords
In SQL, some of the important keywords are:
SELECT, INSERT, UPDATE, DELETE, FROM, WHERE, JOIN, ON, GROUP BY, ORDER BY, ASC, DESC, DISTINCT, IN, NOT IN, LIKE, NOT LIKE, BETWEEN, NOT BETWEEN, AND, OR
Understanding and mastering these keywords is crucial for effective querying and manipulation of data in a database.
SQL Stored Procedures
Stored procedures are a set of pre-written SQL commands that can be stored on the database server for repeated use. They are commonly used to improve database performance and security.
When a stored procedure is created, it is given a name and saved in the database. The stored procedure can then be called by a program or another SQL command.
To create a stored procedure, use the CREATE PROCEDURE statement, followed by the SQL commands to be included in the procedure. The parameters for the procedure can also be declared using the DECLARE statement. Once created, the stored procedure can be executed using the EXECUTE statement.
Stored procedures offer several benefits, including:
- Improved performance: Since stored procedures are pre-compiled, they can execute faster than dynamically created SQL commands. - Increased security: Access to the underlying tables can be restricted, helping to prevent unauthorized access to sensitive data. - Modular programming: Stored procedures can be called from within other procedures, allowing for modular programming and easier maintenance.
Overall, stored procedures are a powerful tool for managing and improving the performance and security of a database.