SQL Overview and Key Topics Covered

SQL Importance

• Widely used in many industries.
• Essential skill for beginners and core for many advanced data jobs.

Course Structure

• 16 videos covering topics from basics to advanced SQL concepts.
• Starts with definitions, syntax, examples, and practical applications.
• Comes with downloadable PDF materials for easy revision.

Key Topics Covered

Introduction to SQL

• Definition: Structured Query Language - A programming language used to interact with databases.
• Importance: Allows data management similar to how language enables human communication.
• Applications: CRUD operations (Create, Read, Update, Delete).
• Difference between SQL and NoSQL databases.

SQL Commands

Types of SQL Commands

1. DDL (Data Definition Language) Commands: CREATE, ALTER, DROP
2. DML (Data Manipulation Language) Commands: INSERT, UPDATE, DELETE
3. DCL (Data Control Language) Commands: GRANT, REVOKE

Databases

• Definition: A system that stores and organizes data.
• Differences between Excel and Database Storage.
• Examples of popular SQL databases: PostgreSQL, MySQL, Microsoft SQL Server, Oracle, Amazon RDS.

Database Structure

• Hierarchical structure: Database -> Tables -> Rows and Columns
• Relational Database Management System (RDBMS) concepts (Primary Key, Foreign Key)

Data Types

• Numeric: INTEGER, FLOAT
• String: CHAR, VARCHAR
• Date and Time: DATE, TIMESTAMP
• Importance of defining data types for accurate and reliable data storage.

Primary and Foreign Keys

• Primary Key: A unique identifier for a row in a table, cannot be null.
• Foreign Key: A column that creates a relationship between two tables.

Constraints

• Ensure data integrity and accuracy.
• Types: NOT NULL, UNIQUE, PRIMARY KEY, FOREIGN KEY, CHECK, DEFAULT
• Applied while creating tables.

SQL Select Statements

• Fundamental for retrieving data: SELECT column_names FROM table_name.
• Filtering records using WHERE clause.
• Sorting data using ORDER BY clause.
• Limiting results using LIMIT clause.

Operators in SQL

• Arithmetic: +, -, *, /
• Comparison: =, !=, >, <
• Logical: AND, OR, NOT
• Bitwise: &, |*

Functions in SQL

String Functions

• UPPER, LOWER, LENGTH, SUBSTRING, CONCAT, REPLACE, TRIM

Aggregate Functions

• COUNT, SUM, AVG, MAX, MIN

Date and Time Functions

• NOW(), CURDATE(), CURTIME(), YEAR(), MONTH(), DAY(), HOUR(), MINUTE(), SECOND()

Group By and Having Clauses

• Grouping results using GROUP BY clause.
• Filtering groups using HAVING clause.

Joins in SQL

• Combining data from multiple tables.

Types of Joins

• INNER JOIN: Returns common records from both tables.
• LEFT JOIN (OUTER): Returns all records from the left table, with matching records from the right table.
• RIGHT JOIN (OUTER): Returns all records from the right table, with matching records from the left table.
• FULL JOIN (OUTER): Returns all records when there is a match in either left or right table.

Self Join and Union

• Self Join: Joining a table to itself.
• Union vs. Union All: Combining results of two queries; UNION removes duplicates, UNION ALL includes them.

Subqueries

• Nested queries within another query.
• Using IN, EXISTS, and comparison operators in subqueries for filtering results.

Windows Functions

• Apply aggregate, ranking, and analytical functions over a specific window (subset) of data.
• Examples: ROW_NUMBER(), RANK(), DENSE_RANK(), NTILE(), LEAD(), LAG()

Case Statements

• Used for conditional logic in SQL queries for different situations.
• Two types: CASE WHEN for conditions, CASE expressions for hard-coded values.

Common Table Expressions (CTE)

• WITH clause to create temporary named result sets that can be referenced within the main query.
• Used for simplifying complex queries, recursive queries.

Tools and Best Practices

• Always keep your queries optimized and efficient.
• Include comments in your queries for clarity.
• Practice using real-world problems and datasets to strengthen SQL skills.

Additional Notes

• SQL is case insensitive, but it’s a good practice to use uppercase for SQL keywords.
• Ensure backup of your databases and understand basic database administration skills.