Databases and data warehouses both are databases and both contains number of rows and columns of tables containing data. Data warehouse is really different from databases because data warehouse helps in creating a sustainable analysis. It is designed for analysis facilities and query facilities. The data that is stored in a data warehouse is multi dimensional and in databases it ensures that the solution is scalable and managed in a better way and answers the questions easily and very effectively. In most of the companies, managers are most interested in knowing about the buying patterns of the group of the customers rather dealing with only one customer and only one purchase. It is easily found in the data warehouses decision support system if the sale has been just made.
Most businesses have not just one large database for all their data, both current and historical because in one single database the data is more risky and it becomes easy for a hackers to steal the data, they would achieve their target very easily because if they hack this one single database which is very large in its size they will also save their cost and money and will achieve their target very easily. If you have only one database you will require giving details to some form of access to sales, research and marketing. Most companies have multiple domains and they control their data in these multiple locations. Big companies always host multiple databases with huge number of small systems.