10. MySQL Part 1: Install, Create, Insert and SELECT
10.5 SELECT Basics and WHERE
SELECT mhanje prashna vicharne. WHERE mhanje filter – kontya rows pahijet.
SELECT * FROM students; -- all columns (avoid in apps)
SELECT name, city FROM students; -- chosen columns
SELECT name, fees_paid FROM students WHERE city = 'Pune';
SELECT name, age FROM students WHERE age > 25;
SELECT name FROM students WHERE city = 'Nagpur' AND fees_paid >= 10000;
SELECT name FROM students WHERE city = 'Pune' OR city = 'Nashik';
SELECT name FROM students WHERE NOT city = 'Pune';
SELECT name FROM students WHERE city <> 'Pune'; -- same as above
| Operator | Meaning |
|---|---|
=, <> or != |
Equal, not equal |
>, <, >=, <= |
Comparisons |
AND, OR, NOT |
Combine conditions (use brackets to be clear) |
Sample output of SELECT name, fees_paid FROM students WHERE city = 'Pune';
| name | fees_paid |
|---|---|
| Ravindra Bagale | 15000.00 |
| Shraddha Bagale | 15000.00 |
| Rani | 15000.00 |
Why this matters for security
The classic injection ' OR '1'='1 works because OR with an always-true condition makes the WHERE clause match every row – for a login query, that means "logged in without a password". Once you understand WHERE, you understand why that payload works.
Ravindra Bagale's Tip
AND aani OR ekatra vaparla aani brackets nahi dile tar chukiche rows yetat – khup students ithe fastat. AND aadhi evaluate hota. Shanka asel tar nehmi brackets: WHERE (city='Pune' OR city='Nashik') AND age > 25.
Practice task
Show students from Nagpur; students older than 24 who paid 15000; and students not from Pune – three separate queries.