In the example above, each Person has a Name, Date of Birth, Gender and Height. The Id column is the key that identifies one person in the table. You use the keyword `PRIMARY KEY` to configure one or more columns as a primary key.
Just to understand the above code, the datatype mentioned indicates the following type of values approximately.
```
int : A whole number
varchar : Strings
date : A Date Value without Time component
bit : A Boolean value
numeric(5, 2): A decimal value with ( Precision 5 and Scale 2 )
ie. Total of 5 digits with 3 digits before the decimal point and 2 digits after decimal point.
```
Proper List and meaning of datatypes can be refered from resources like this: ( https://www.w3schools.com/sql/sql_datatypes.asp )
##### Default and Not NULL
When a row of values are inserted into a table, any column which is marked as `not null` and without a `default` value will be compulsary. Insert fails otherwise.
If no value is provided for a column which has a `default` value, insert will succeed with the column being assigned the default value defined in the table definition.
>e.g Column Weight has default value as 50.
By default all columns are nullable ie. `null` is assumed unless explicity set as `not null`. So any column without `default` and `not null` keyword can be skipped in insert commands. They will have *null* value on querying.
>e.g Column WaistSize can be *null*
>Please note that `null` and `` (Blank) are queried and handled differently in most Databases.