A data type determines the type of data that can be stored in a database table column. When we create a table, we should define the proper data type for each column, as per its storage requirement. For example, a SMALLINT occupies 2 bytes of space, while an INT occupies 4 bytes of space. When we define the INT data type, it means that we must store all 4 bytes into that column every time. If we are storing a number like 10 or 20, then it's a waste of bytes. This will eventually make your reads slower because the database must read over multiple sectors of the disk. Also, choosing the right data type helps us store the right data into the column. For example, if we use the date data type for a column, then the database does not allow any string and numeric data in a column that does not represent a date.