There can be string data type and numeric data type to declare the attribute and specify the type of value that can be contained by a column.
For example VARCHAR, CHAR etc are examples of commonly used string data types that can hold alphanumeric characters and also special characters.
INT, FLOAT, DECIMAL, etc are examples of numeric data types that can hold numerical values. For example you would not want to use numeric data type for name attribute of person entity.
However it might be better to declare an attribute that contains only digits as a string data type as character data type can also hold digits.
For example a social security number attribute can be declared as character data type instead of numeric data type. Although a social security number only consists of digits but it can be declared as a character data type because there is no need of performing any mathematical operations on a social security number. It is just a combination of digits and it might not need to be subtracted, added, multiplied etc.
Another example can be of a phone number. It also is a combination of digits but again there is no need to perform mathematical functions over a phone number attribute. But as we know there are different area codes for different countries, so there might be a need of adding or removing an area code with a phone number. So it is appropriate to declare such an attribute as a character data type.
