Can we use single database in microservices?

Does microservices use multiple databases?

It means that we can use different database technologies for different microservices. So one service may use an SQL database and another one a NoSQL database. That's feature allows using the most efficient database depending on the service requirements and functionality.

Do microservices need to have separate databases?

As you described it very well above, each microservice needs to own it's DATA, which could be held within a dedicated database, within a dedicated schema (within a database), or even a set of dedicated tables (within a schema within a database).

Why each microservice has its own database?

It would allow you to pick the database technology which fits your Business requirement best in order to get the best performance or usage of it. For example some specific micro-service might have some Read-heavy operations with very complex filter options and a full text search requirement.

Should microservices share a database instance?

The answer would be "no" more often than not. So by having a database instance per microservice (physically or logically) already gives you a lot in terms of "loose coupling and cohesive behaviour" as you don't share databases. Another concern are breaking changes to the database between versions of the microservice.