Datetime functions related to convert StringType to/from DateType or TimestampType.For example, unix_timestamp, date_format, to_unix_timestamp, from_unixtime, to_date, to_timestamp, from_utc_timestamp, to_utc_timestamp, etc.
Number(n): The n here represents the maximum count of letters this type of datetime pattern can be used. If the count of letters is one, then the value is output using the minimum number of digits and without padding. Otherwise, the count of digits is used as the width of the output field, with the value zero-padded as necessary.
Zone names(z): This outputs the display textual name of the time-zone ID. If the count of letters is one, two or three, then the short name is output. If the count of letters is four, then the full name is output. Five or more letters will fail.
Optional section start and end: Use  to define an optional section and maybe nested.During formatting, all valid data will be output even it is in the optional section.During parsing, the whole section may be missing from the parsed string.An optional section is started by [ and ended using ] (or at the end of the pattern). 041b061a72