Answer:
Data definition in SQL is via the create statement. The statement can be used to create a table, index, or view (i.e., a virtual table based on existing tables). To create a table, the create statement specifies the name of the table and the names and data types of each column of the table. Its format is:
create table (relation> (<attribute list>)
where the attribute list is specified as:
<attribute list> :: = <attribute name> (<data type>)[not null] <attribute list>
The data types supported by SQL depend on the particular implementation. However, the following data types are generally included: integer, decimal, real (i.e., floating point values), and character strings, both of fixed size and varying length. A number of ranges of values for the integer data type are generally supported, for example, integer and smallint. The decimal value declaration requires the specification of the total number of decimal digits for the value and (optionally), the number of digits to the right of the decimal point. The number of fractional decimal digits is assumed to be zero if only the total number of digits is specified.
<data type> :: = <integer> | <smallint> | <char(n)> | <float> | <decimal (p[q])>
In addition, some implementations can support additional data types such as bit strings, graphical strings, logical, data, and time. Some DBMSs support the concept of date. One possible implementation of date could be as eight unsigned decimal digits representing the data in the yyyymmdd format. Here yyyy represents the year, mm represents the month and dd represents the day. Two dates can be compared to find the one that is larger and hence occurring later. The system ensures that only legal date values are inserted (19860536 for the date would be illegal) and functions are provided to perform operations such as adding a number of days to a date to come up with another date or subtracting a date from the current date to find the number of days, months, or years. Date constants are provided in either the format given above or as a character string in one of the following formats: mm/dd/yy; mm/dd/yyyy; dd-mm-yy; dd-mm-yyyy. In this unit, we represent a date constant as eight unsigned decimal digits in the format yyyymmdd.
