Comparison Operators in WHERE (PostgreSQL)

We’ve already seen that the WHERE keyword allows us to filter rows returned by a query.

In simple words:

WHERE checks each row one by one and decides whether it should appear in the final result.

Let’s now look at different comparison operators we can use inside a WHERE clause.

Recap: Filtering with WHERE

Consider this query:

select
  name,
  area
from cities
where area > 4000;

What happens here is very simple:

• PostgreSQL looks at each row
• It checks the area value
• Only rows with area > 4000 are returned

That’s why we only see cities like Tokyo and Shanghai.

Equality Check (=)

We can also check if a column value is exactly equal to something.

For example, let’s find the city with an area equal to 8223:

select
  name,
  area
from cities
where area = 8223;

Important Note

In SQL:

• = is not assignment
• it is a comparison operator

We are not changing anything — we are just checking a condition.

Result

This query returns:

• Tokyo

Because Tokyo is the only city with an area of 8223.

Not Equal (!=)

We can also check for values that are not equal.

select
  name,
  area
from cities
where area != 8223;

This returns: