MySQL WHERE

The WHERE clause specifies a condition that records must satisfy.

SELECT *
FROM students
WHERE age = 20;

This query returns only students whose age is 20.

The basic syntax is:

SELECT column_name
FROM table_name
WHERE condition;

Example:

SELECT name
FROM students
WHERE age = 21;

The equal operator = checks whether two values are equal.

SELECT *
FROM students
WHERE course = 'Python';

This returns students enrolled in Python.

Numeric values can be compared directly.

SELECT *
FROM students
WHERE age = 25;

There is no need to put numeric values inside quotes.

Text values are normally written inside quotes.

SELECT *
FROM students
WHERE name = 'Rahul';

This returns records where the name matches the specified value.

The > operator returns values greater than the specified value.

SELECT *
FROM students
WHERE age > 18;

This returns students older than 18.

The < operator returns values less than the specified value.

SELECT *
FROM students
WHERE age < 25;

This returns students whose age is less than 25.

The >= operator checks for values greater than or equal to a specified value.

SELECT *
FROM students
WHERE age >= 18;

The <= operator checks for values less than or equal to a specified value.

SELECT *
FROM students
WHERE fee <= 15000;

The != operator checks for values that are not equal.

SELECT *
FROM students
WHERE course != 'Python';

This returns students whose course is not Python.

MySQL also supports <> as a not-equal operator.

SELECT *
FROM students
WHERE age <> 20;

This returns records where age is not 20.

The AND operator allows multiple conditions.

SELECT *
FROM students
WHERE age > 18
AND course = 'Python';

Both conditions must be true.

The OR operator returns records when at least one condition is true.

SELECT *
FROM students
WHERE course = 'Python'
OR course = 'Java';

You can use more than two conditions with AND.

SELECT *
FROM students
WHERE age > 18
AND fee > 10000
AND course = 'Python';

All three conditions must be satisfied.

AND and OR can be combined in one query.

SELECT *
FROM students
WHERE course = 'Python'
AND (age > 20 OR fee > 15000);

Parentheses help clearly define the logical condition.

BETWEEN can be used to filter values within a range.

SELECT *
FROM students
WHERE age BETWEEN 18 AND 25;

This includes values from 18 through 25.

IN checks whether a value matches one of several specified values.

SELECT *
FROM students
WHERE course IN ('Python', 'Java', 'PHP');

This returns students enrolled in any of the listed courses.

LIKE is used for pattern matching.

SELECT *
FROM students
WHERE name LIKE 'A%';

This finds names beginning with the letter A.

Use IS NULL to find records where a column contains NULL.

SELECT *
FROM students
WHERE mobile IS NULL;

Do not use = NULL to test for NULL values.

IS NOT NULL finds records where a value exists.

SELECT *
FROM students
WHERE mobile IS NOT NULL;

WHERE can be used with UPDATE to modify specific records.

UPDATE students
SET fee = 16000
WHERE id = 1;

Only the student with ID 1 is updated.

WHERE can be used with DELETE to remove specific records.

DELETE FROM students
WHERE id = 5;

Only the record with ID 5 is deleted.

WHERE can also filter decimal values.

SELECT *
FROM students
WHERE fee > 10000.00;

This returns students whose fee is greater than 10,000.

WHERE can be used to filter date values.

SELECT *
FROM students
WHERE admission_date = '2026-09-21';

This returns students admitted on the specified date.

WHERE can be combined with ORDER BY.

SELECT name, course, fee
FROM students
WHERE fee > 10000
ORDER BY fee DESC;

First the records are filtered, then the matching records are sorted.

WHERE can also be combined with LIMIT.

SELECT *
FROM students
WHERE course = 'Python'
LIMIT 5;

This returns up to five Python students.

Suppose we want students who are older than 20 and enrolled in Python.

SELECT id, name, mobile, course
FROM students
WHERE age > 20
AND course = 'Python';

• Forgetting the WHERE condition
• Using incorrect column names
• Forgetting quotes around text values
• Using = NULL instead of IS NULL
• Writing an invalid comparison operator
• Using AND when OR is required
• Using OR when all conditions must be true

A simple WHERE workflow is:

1. Select the required columns.
2. Specify the table.
3. Write the WHERE keyword.
4. Write the condition.
5. Add AND or OR when necessary.
6. Add ORDER BY or LIMIT if required.

SELECT name, course, fee
FROM students
WHERE fee > 10000
AND age >= 18
ORDER BY fee DESC
LIMIT 5;

CREATE TABLE students (
    id INT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(100),
    course VARCHAR(100),
    age INT,
    fee DECIMAL(10,2)
);

INSERT INTO students
(name, course, age, fee)
VALUES
('Rahul', 'Python', 22, 15000.00),
('Priya', 'Java', 21, 18000.00),
('Amit', 'Python', 24, 12000.00),
('Neha', 'PHP', 20, 10000.00);

SELECT id, name, course, fee
FROM students
WHERE course = 'Python'
AND fee > 10000
ORDER BY fee DESC;

This query finds Python students whose fee is greater than 10,000 and displays them in descending fee order.