Overview of Date Functions
The following explains the difference between the types
of date functions:
Standard date functions
are for use with standard date formats, or just date formats. A
date format refers to internally stored data that is capable of holding
date components, such as century, year, quarter, month, and day.
It does not include time components. A synonym does not specify
an internal data type or length for a date format. Instead, it specifies
display date components, such as D (day), M (month), Q (quarter),
Y (2-digit year), or YY (4-digit year). For example, format MDYY
is a date format that has three date components; it can be used
in the USAGE attribute of a synonym. A real date value, such as
March 9, 2004, described by this format is displayed as 03/09/2004,
by default. Date formats can be full component and non-full component.
Full component formats include all three letters, for example, D,
M, and Y. JUL for Julian can also be included. All other date formats
are non-full component. Some date functions require full component
arguments for date fields, while others will accept full or non-full
components. A date format was formerly called a smart date.
Legacy date functions
are for use with legacy dates only. A legacy date refers to formats
with date edit options, such as I6YMD, A6MDY, I8YYMD, or A8MDYY. For
example, A6MDY is a 6-byte alphanumeric string. The suffix MDY indicates
the order in which the date components are stored in the field,
and the prefix I or A indicates a numeric or alphanumeric form of
representation. For example, a value '030599' can be assigned to
a field with format A6MDY, which will be displayed as 03/05/99.
Date formats have an internal representation matching either
numeric or alphanumeric format. For example, A6MDY matches alphanumeric
format, YYMD and I6DMY match numeric format. When function output
is a date in specified by output, it can be used either for
assignment to another date field of this format, or it can be used
for further data manipulation in the expression with data of matching
formats. Assignment to another field of a different date format,
will yield a random result.
All but three date functions deal with only one
date format. The exceptions are DATECVT, HCNVRT, and HDATE, which
convert one date type into another.