SQL WHERE Clause — Filtering Data

The class teacher wants students who scored at least 85, including students exactly on that boundary.

WHERE keeps rows whose condition evaluates to true. False and unknown conditions do not qualify a row.

A comparison such as marks >= 85 is evaluated for each candidate row. AND combines required conditions; OR accepts either alternative. Parentheses make combined conditions explicit. A NULL mark makes an ordinary numeric comparison unknown, so it is not included by that comparison.

Related concepts: Combine SQL Conditions and Missing Values and NULL and Filter Groups with HAVING.

Imagine walking into a school library and asking for *every* book. Not practical, right? Instead, you specify — “Books by R.K. Narayan” or “Books for Class 10.” SQL works the same way. The WHERE clause lets you filter records and get only what matters.

SQL · portable concepts; preserved examples identify their engine

SELECT column1, column2, ...
FROM table_name
WHERE condition;

SQL · portable concepts; preserved examples identify their engine

We’ll use this familiar table for examples:

CREATE TABLE students (
  roll_no INT PRIMARY KEY,
  name VARCHAR(50),
  class VARCHAR(10),
  age INT,
  city VARCHAR(30)
);

INSERT INTO students VALUES
(1, 'Aarav Sharma', '10A', 15, 'Delhi'),
(2, 'Diya Iyer', '9B', 14, 'Chennai'),
(3, 'Rohit Menon', '10A', 15, 'Kochi'),
(4, 'Sneha Patil', '8C', 13, 'Pune'),
(5, 'Mehul Agarwal', '9B', 14, 'Delhi');

SQL · portable concepts; preserved examples identify their engine

Use case: A school administrator wants to retrieve a list of all students enrolled in class '9B' to prepare a class roster.

SQL query description: SQL query to select the name and class columns from the students table where the class is exactly '9B'.

SELECT name, class FROM students
WHERE class = '9B';

Result: Result contains the names and class details of students who are enrolled in class '9B'.

The surrounding query explains the specific highlighted values. Highlights annotate this example; they do not change the stored table.

SQL · portable concepts; preserved examples identify their engine

Use case: A school administrator wants to retrieve a list of all students who are 15 years old to assign them to an age-specific program.

SQL query description: SQL query to select the name and age columns from the students table where the age is equal to 15.

SELECT name, age FROM students
WHERE age = 15;

Result description: Result contains the names and ages of students who are exactly 15 years old.

The surrounding query explains the specific highlighted values. Highlights annotate this example; they do not change the stored table.

SQL · portable concepts; preserved examples identify their engine

Use case: A school administrator wants to get the names of students who are enrolled in class '9B' and reside in the city of Delhi for location-specific communication or reporting.

SQL query description: SQL query to select the name column from the students table where the city is 'Delhi' and the class is '9B'.

SELECT name FROM students
WHERE city = 'Delhi' AND class = '9B';

Result description: Result contains the names of students who belong to class '9B' and live in Delhi.

The surrounding query explains the specific highlighted values. Highlights annotate this example; they do not change the stored table.

SQL · portable concepts; preserved examples identify their engine

Use case: A school administrator wants to generate a list of students who are from the cities of Delhi or Pune for city-wise reporting or regional event planning.

SQL query description: SQL query to select the name and city columns from the students table where the city is either 'Delhi' or 'Pune'.

SELECT name, city FROM students
WHERE city = 'Delhi' OR city = 'Pune';

Result description: Result contains the names and city information of students who reside in either Delhi or Pune.

The surrounding query explains the specific highlighted values. Highlights annotate this example; they do not change the stored table.

SQL · portable concepts; preserved examples identify their engine

Use case: A school administrator wants to get a list of students who are not from the city of Delhi to organize regional events for out-of-town students.

SQL query description: SQL query to select the name and city columns from the students table where the city is not equal to 'Delhi'.

SELECT name, city FROM students
WHERE NOT city = 'Delhi';

Result description: Result contains the names and city information of all students who do not belong to Delhi.

The surrounding query explains the specific highlighted values. Highlights annotate this example; they do not change the stored table.

SQL · portable concepts; preserved examples identify their engine

Use case: A school administrator wants to retrieve a list of students who are aged between 14 and 15 to plan age-specific academic programs.

SQL query description: SQL query to select the name and age columns from the students table where the age is between 14 and 15, inclusive.

SELECT name, age FROM students
WHERE age BETWEEN 14 AND 15;

Result description: Result contains the names and ages of students who are either 14 or 15 years old.

The surrounding query explains the specific highlighted values. Highlights annotate this example; they do not change the stored table.

SQL · portable concepts; preserved examples identify their engine

Use case: A school administrator wants to identify students who are from the cities of Delhi or Chennai in order to organize city-specific events or communications.

SQL query description: SQL query to select the name and city columns from the students table where the city is either 'Delhi' or 'Chennai'.

SELECT name, city FROM students
WHERE city IN ('Delhi', 'Chennai');

Result description: Result contains the names and city information of students who belong to Delhi or Chennai.

The surrounding query explains the specific highlighted values. Highlights annotate this example; they do not change the stored table.

SQL · portable concepts; preserved examples identify their engine

Use case: A school administrator wants to find all students whose names start with the letter 'S' for organizing name-based reports or communications.

SQL query description: SQL query to select the name column from the students table where the name begins with the letter 'S', using the LIKE operator with the pattern 'S%'.

SELECT name FROM students
WHERE name LIKE 'S%';

Result description: Result contains the names of all students whose names start with the letter 'S'.

The surrounding query explains the specific highlighted values. Highlights annotate this example; they do not change the stored table.

SQL · portable concepts; preserved examples identify their engine

• = (equal)
• != or <> (not equal)
• < (less than)
• > (greater than)
• <=, >=

Example: Students younger than 14

Use case: A school administrator wants to retrieve a list of all students who are younger than 14 years old to identify students eligible for a junior program.

SQL query description: SQL query to select the name and age columns from the students table where the age is less than 14.

SELECT name, age FROM students
WHERE age < 14;

Result description: Result contains the names and ages of students whose age is less than 14.

The surrounding query explains the specific highlighted values. Highlights annotate this example; they do not change the stored table.

• Use quotes for string values, but not for numbers.
• Use parentheses to group conditions when mixing AND/OR.
• Preview with SELECT before applying updates or deletes.

Use >= when the boundary is included and > when it is excluded. Use IS NULL for missing values. A WHERE condition on the right side of a LEFT JOIN can remove the unmatched rows that the join originally preserved.

List students with marks at least 85 and predict whether 85 itself qualifies.

This practice uses a separate, fresh fixture named practice_students. It does not continue the changing table state of the earlier examples.

SQL · create only these practice tables in a disposable database:

CREATE TABLE practice_students (roll_no INTEGER PRIMARY KEY, name VARCHAR(50), class VARCHAR(10), marks INTEGER, city VARCHAR(30));
INSERT INTO practice_students VALUES
(1, 'Aarav', '10A', 85, 'Pune'),
(2, 'Diya', '9B', 70, 'Chennai'),
(3, 'Sneha', '10A', 85, 'Pune');

This practice uses a separate, fresh fixture named practice_students. It does not continue the changing table state of the earlier examples.

SQL · create only these practice tables in a disposable database:

CREATE TABLE practice_students (roll_no INTEGER PRIMARY KEY, name VARCHAR(50), class VARCHAR(10), marks INTEGER, city VARCHAR(30));
INSERT INTO practice_students VALUES
(1, 'Aarav', '10A', 85, 'Pune'),
(2, 'Diya', '9B', 70, 'Chennai'),
(3, 'Sneha', '10A', 85, 'Pune');

SQL · this practice variation runs with SQLite 3; the preserved examples retain their stated dialect

SELECT name, marks FROM practice_students WHERE marks >= 85 ORDER BY roll_no;

Both 85-valued rows satisfy >=. Replacing it with > would exclude both, so the boundary changes the result.

WHERE keeps rows whose condition evaluates to true. False and unknown conditions do not qualify a row.

Both 85-valued rows satisfy >=. Replacing it with > would exclude both, so the boundary changes the result.

Continue your understanding with Combine SQL Conditions and Missing Values and NULL and Filter Groups with HAVING.

Source for the engine-specific behavior: MySQL 8.4 reference documentation.