# MDY Date (dash-separated) Key: `datetime.date.mdy_dash` Month-Day-Year with dash separators and 4-digit year. US database exports. Ambiguous with dmy\_dash when day \<= 12. Page: Format: `%m-%d-%Y` Samples: `01-15-2024`, `12-31-2023`, `06-01-2000` ## Background ### Origin In traditional American usage, dates are written in month–day–year order.[[1]](https://en.wikipedia.org/wiki/Date_and_time_notation_in_the_United_States) Wikipedia describes the American month–day–year order as middle endian, since it follows neither increasing nor decreasing order of significance.[[1]](https://en.wikipedia.org/wiki/Date_and_time_notation_in_the_United_States) The slash is the most commonly used separator in the all-numeric American date.[[1]](https://en.wikipedia.org/wiki/Date_and_time_notation_in_the_United_States) According to Wikipedia, the hyphen and the period have also emerged as separators in the all-numeric American date recently, due to globalisation.[[1]](https://en.wikipedia.org/wiki/Date_and_time_notation_in_the_United_States) Microsoft SQL Server's CONVERT function lists style 110, under the standard USA, as MM-dd-yyyy.[[2]](https://learn.microsoft.com/en-us/sql/t-sql/functions/cast-and-convert-transact-sql) SQL Server's style 10, also listed under USA, is the two-digit-year form MM-dd-yy.[[2]](https://learn.microsoft.com/en-us/sql/t-sql/functions/cast-and-convert-transact-sql) FineType labels the dash-separated month-day-year date with a four-digit year datetime.date.mdy\_dash, with the format string %m-%d-%Y.[[3]](https://raw.githubusercontent.com/meridian-online/finetype/main/labels/definitions_datetime.yaml) ### Use Wikipedia reports that the Chicago Manual of Style discourages all-numeric dates other than the ISO 8601 year-month-day form, as they are not comprehensible to readers outside the United States.[[1]](https://en.wikipedia.org/wiki/Date_and_time_notation_in_the_United_States) Wikipedia notes that American date styles have influenced date notation in Canada, creating confusion in international commerce.[[1]](https://en.wikipedia.org/wiki/Date_and_time_notation_in_the_United_States) Microsoft SQL Server's style 105, listed as Italian, writes dates as dd-MM-yyyy.[[2]](https://learn.microsoft.com/en-us/sql/t-sql/functions/cast-and-convert-transact-sql) A dash-separated date such as 06-01-2000 is valid read either way round, so a single value cannot tell you whether a file is month-first or day-first. (Meridian's view) Scan the whole column before choosing: a first part above 12 means day-first, a second part above 12 means month-first, and a column with neither stays ambiguous until you ask whoever produced it. (Meridian's view) In pandas, the dayfirst parameter of to\_datetime defaults to False.[[4]](https://pandas.pydata.org/docs/reference/api/pandas.to_datetime.html) The pandas documentation says that with dayfirst set to True, "10/11/12" is parsed as 2012-11-10.[[4]](https://pandas.pydata.org/docs/reference/api/pandas.to_datetime.html) The pandas documentation warns that dayfirst=True is not strict, but will prefer to parse with day first.[[4]](https://pandas.pydata.org/docs/reference/api/pandas.to_datetime.html) Give the parser an explicit format such as %m-%d-%Y rather than letting it guess the order. (Meridian's view) In DuckDB's format specifiers, %m is the month as a zero-padded decimal number.[[5]](https://duckdb.org/docs/current/sql/functions/dateformat) In DuckDB's format specifiers, %d is the day of the month as a zero-padded decimal.[[5]](https://duckdb.org/docs/current/sql/functions/dateformat) DuckDB's strptime function throws an error on failure.[[5]](https://duckdb.org/docs/current/sql/functions/dateformat) DuckDB's documentation points to try\_strptime for returning NULL on failure.[[5]](https://duckdb.org/docs/current/sql/functions/dateformat) DuckDB accepts a DATEFORMAT when parsing CSV files, either in the COPY statement or in the read\_csv function.[[5]](https://duckdb.org/docs/current/sql/functions/dateformat) Wikipedia notes that year-month-day dates such as ISO 8601's YYYY-MM-DD list chronologically when sorted alphanumerically.[[1]](https://en.wikipedia.org/wiki/Date_and_time_notation_in_the_United_States) Convert month-day-year strings to a real date type, or to ISO 8601 text, before you sort or store them. (Meridian's view) ## Sources 1. [Date and time notation in the United States](https://en.wikipedia.org/wiki/Date_and_time_notation_in_the_United_States) — secondary source 2. [CAST and CONVERT (Transact-SQL) - SQL Server \| Microsoft Learn](https://learn.microsoft.com/en-us/sql/t-sql/functions/cast-and-convert-transact-sql) — documentation 3. [definitions\_datetime.yaml](https://raw.githubusercontent.com/meridian-online/finetype/main/labels/definitions_datetime.yaml) — FineType 4. [pandas.to\_datetime — pandas 3.0.6 documentation](https://pandas.pydata.org/docs/reference/api/pandas.to_datetime.html) — documentation 5. [Date Format Functions – DuckDB](https://duckdb.org/docs/current/sql/functions/dateformat) — documentation