What is SQL?
SQL stands for Structured Query Language. It’s how we talk to databases — like asking a big library to find or organize books for you.
What is a database?
A database is like a smart, organized digital notebook where you keep stuff: names, numbers, notes, anything!
What is a table?
A table is like a spreadsheet with rows and columns. Each row is one item (like a person), and each column is a detail (like their name or age).
Basic SQL commands:
- SELECT – Ask the database to show something
- INSERT – Add something new
- UPDATE – Change something
- DELETE – Remove something
What is a primary key?
A special column that helps tell rows apart — like a student ID. Every row must have a different one.
What is a foreign key?
A column that connects one table to another — like saying “this book belongs to that student.”
What is JOIN?
JOIN is like building a bigger table by combining info from two smaller tables. You can:
- INNER JOIN: only matching rows
- LEFT JOIN: all from the left, plus matching from right
- RIGHT JOIN: all from the right, plus matching from left
- FULL JOIN: all rows from both
What is WHERE?
It’s like adding a filter. “Show me only students older than 10.”
What is ORDER BY?
It sorts your answers — like sorting names alphabetically or scores from highest to lowest.
What is GROUP BY?
Group things together and get totals, averages, etc. “Group by class and count how many students.”
What is NULL?
NULL means “nothing here.” It’s like an empty box. Not 0, not blank — just not known.
What is INDEX?
An index is like a shortcut to find data faster — like a book’s index page.
What is a transaction?
A set of steps that must all work or none do. Like building LEGO: if one brick falls, you take it all apart and start over.
What is normalization?
A way to organize data to avoid repeats. Instead of writing a teacher’s name in every student row, you put teachers in a separate table and link it.
What is SQL injection?
A trick bad people use to sneak fake commands into your database. That’s why we never trust user input!
What is a view?
A saved SQL query that acts like a pretend table. You can use it like a shortcut to get common results.
What is a stored procedure?
A saved set of SQL steps you can run again and again — like a recipe.
What is ACID in databases?
- A: Atomic – all or nothing
- C: Consistent – always follows rules
- I: Isolated – no mix-ups with other actions
- D: Durable – even if power goes out, the result stays
What is a schema?
A plan that says what tables are in your database and what’s in each table.
Final tip:
SQL is like talking to a robot librarian — be clear, specific, and careful with your words!