WHERE Clause in SQL

Suppose a Students table contains many records. If you want to find only students who are 20 years old, you can use WHERE.

SELECT *
FROM Students
WHERE age = 20;

Only records where the age is 20 will be returned.

SELECT column1, column2
FROM table_name
WHERE condition;

The condition determines which records should be returned.

SELECT *
FROM Students
WHERE age = 21;

This retrieves all columns for students whose age is 21.

SELECT name
FROM Students
WHERE age = 21;

Only the names of students whose age is 21 are returned.

Text values are normally written inside single quotes.

SELECT *
FROM Students
WHERE course = 'Python';

This retrieves students enrolled in Python.

SELECT *
FROM Students
WHERE age = 20;

Numeric values normally do not require quotation marks.

The = operator checks whether two values are equal.

SELECT *
FROM Students
WHERE age = 20;

SELECT *
FROM Students
WHERE age > 20;

This returns students whose age is greater than 20.

SELECT *
FROM Students
WHERE age < 20;

This returns students whose age is less than 20.

SELECT *
FROM Students
WHERE age >= 20;

This returns students whose age is 20 or greater.

SELECT *
FROM Students
WHERE age <= 20;

This returns students whose age is 20 or less.

The <> operator means not equal.

SELECT *
FROM Students
WHERE course <> 'Python';

This returns students whose course is not Python.

In MySQL, != can also be used for not equal.

SELECT *
FROM Students
WHERE age != 20;

Use AND when all specified conditions must be true.

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

Both conditions must be satisfied.

Use OR when at least one condition should be true.

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

The NOT operator reverses a condition.

SELECT *
FROM Students
WHERE NOT course = 'Python';

This returns students whose course is not Python.

The BETWEEN operator checks whether a value is within a range.

SELECT *
FROM Students
WHERE age BETWEEN 18 AND 25;

The boundary values are included.

The IN operator allows multiple possible values.

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

The LIKE operator 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 has a NULL value.

SELECT *
FROM Students
WHERE mobile IS NULL;

SELECT *
FROM Students
WHERE mobile IS NOT NULL;

This returns records where the mobile column contains a non-NULL value.

WHERE can be combined with ORDER BY.

SELECT *
FROM Students
WHERE age > 18
ORDER BY age DESC;

First the records are filtered, then the result is sorted.

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

In MySQL, this returns up to five matching records.

WHERE is very important when updating specific records.

UPDATE Students
SET fee = 18000
WHERE id = 1;

Only the student whose ID is 1 will be updated.

WHERE can also be used to delete a specific record.

DELETE FROM Students
WHERE id = 5;

Only the record with ID 5 is targeted.

You can combine several conditions.

SELECT *
FROM Students
WHERE age >= 18
AND course = 'Python'
AND city = 'Patna';

All three conditions must be satisfied.

Parentheses can make complex conditions easier to understand and control the logical grouping.

SELECT *
FROM Students
WHERE age > 18
AND (course = 'Python' OR course = 'Java');

This means the student must be older than 18 and must be enrolled in either Python or Java.

WHERE can also filter decimal values such as fees.

SELECT *
FROM Students
WHERE fee > 10000;

This returns students whose fee is greater than 10000.

You can filter records using date values.

SELECT *
FROM Students
WHERE admission_date = '2026-09-20';

This returns records with the specified admission date.

SELECT name, course, fee
FROM Students
WHERE age >= 18
AND fee > 5000
AND course IN ('Python', 'Java')
ORDER BY fee DESC
LIMIT 10;

This query:

• Selects the name, course, and fee columns.
• Finds students aged 18 or above.
• Filters students whose fee is greater than 5000.
• Allows Python or Java courses.
• Sorts the results by fee from highest to lowest.
• Returns up to 10 records.