ORA-01427: single-row subquery returns more than one row

I faced today, "ORA-01427:sub-query returns more than one row" error. The problem is easy to identify:This error is raised, when a sub-query returns more than one row to an Equality or in-Equality operator. The reason being there are restrictions on the legal comparison operators (Screen -1).

Screen -1

For any comparison operator listed in the table shown below, the sub-query must return single row (in other words, the sub-query, must be a single-row sub-query, otherwise it will fail)

Single-row Sub-query Operators

Symbol	Meaning
=	equal
>	greater than
>=	greater than or equal
<	less than
<=	less than or equal
<>	not equal
!=	not equal

The operators in the following table can use multiple-row sub-queries:

Multiple-row Sub-query Operators

Symbol	Meaning
IN	equal to any member in a list
NOT IN	not equal to any member in a list
ANY	returns rows that match any value on a list
ALL	returns rows that match all the values in a list

There are several approaches to resolve this, most popular one being changing the inequality operator to a multiple-row operators (say, if the operator is "=" than change it "IN", "ANY", "ALL", so that it does not matter if multiple rows are returned.).
However, I found that if you use inline views, you can retain inequality operator as shown below in (Screen -2)

Screen -2

Note: In order to get consistent result, use the sub-query based on primary key. The above method is based on unique key