jhorstmann commented on issue #5398:
URL:
https://github.com/apache/arrow-datafusion/issues/5398#issuecomment-1820970911
Having recently implemented this in our proprietary engine, these were my
notes regarding postgres, compared to other pattern syntaxes:
- Seems very exhaustive but also super complex
- Features include years with commas, multipe variants of AM/PM indicates,
roman numerals, complete sub-syntax for number formatting and padding
- In my opinion much too complex to implement, we’d need to define a small
subset, at which point we can no longer claim postgres compatibility
We ended up implementing a pattern syntax closer to the one supported by
Java
[SimpleDateFormat](https://docs.oracle.com/javase/8/docs/api/java/text/SimpleDateFormat.html),
supporting a subset of those pattern characters. Similar syntax is supported
by Presto/TrinoDB/Athena and so should be familiar to our users. My personal
opinion was also that the percent-based syntax from MySQL or chrono looked a
bit ugly, and does not make the width or padding of fields obvious.
Internally we however translated the user-facing syntax to [chrono format
items](https://docs.rs/chrono/latest/chrono/format/enum.Item.html) and used
[chrono::format::parse](https://docs.rs/chrono/latest/chrono/format/fn.parse.html)
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