datestyle

Datestyle, in PostgreSQL, is the DateStyle run-time parameter that governs how date and time values are parsed from text and rendered as text. It does not change the stored values; it only affects input interpretation and textual representation of date and time values.

Format and options: A DateStyle value consists of two components separated by a comma: a date/time style and a calendar order. The first component can be ISO, SQL, or Postgres, and the second component specifies the field order as MDY, DMY, or YMD. Examples include 'ISO, MDY', 'SQL, DMY', or 'Postgres, YMD'. Different combinations influence how textual literals are interpreted and how dates are printed.

Effects: The setting influences how string literals are converted to date/time values when they are ambiguous (for example, 01/02/03). It also determines the text formatting used when date/time values are converted to text, such as in casts, to_char outputs, or client displays. The underlying storage format remains unchanged.

Management: The current setting can be viewed with SHOW DateStyle; it can be changed for a session with SET DateStyle TO 'ISO, DMY'; and can be made persistent in the server configuration file (postgresql.conf) or via system-wide alterations. Some client environments may also influence date style through environment variables such as PGDATESTYLE.

Notes: DateStyle is a PostgreSQL-specific mechanism for controlling date/time I/O formatting. Applications should be aware of the active setting when parsing user input or presenting dates, especially when interacting with data from different sources or platforms.