YearMonthDay

Yearmonthday is a date notation that represents a calendar date by listing its year, month, and day in that order. It is commonly seen as the calendar date form yyyy-mm-dd, as standardized by ISO 8601, or as a compact numeric form yyyymmdd without separators. The year-first arrangement helps ensure unambiguous interpretation across locales that use different day–month orders and supports straightforward lexicographic sorting when encoded as a fixed-width numeric value.

In practice, yearmonthday is used in computing, data interchange, filenames, and databases where an unambiguous, sortable date value is important. The fixed component order makes it easy to compare dates, perform range queries, and index by date. Variants exist with different separators or no separators, depending on system constraints or legacy formats.

When validating yearmonthday values, systems typically enforce that the year, month, and day constitute a valid date in the Gregorian calendar, accounting for leap years and the varying lengths of months. Depending on the context, the date may be stored as a date data type, as a string in the yyyy-mm-dd form, or as an integer in the yyyymmdd form, each with its own implications for storage, validation, and querying.

Yearmonthday supports a range of calendar-related operations, such as comparisons, formatting, and conversions to other date representations. It is a common building block in software dealing with historical records, scheduling, reporting, and data warehousing. See also ISO 8601, calendar date, and lexicographic order.