TSQL-specific CONVERT() can't be parsed

Example:

print(sqlglot.parse_one("SELECT convert([varchar](10),convert([datetime],[My Date],105),23)"))

According to the docs, this means the following:

1. Convert [My Date] to datetime, using date format dd-mm-yyyy.
2. Convert the result to varchar of length 10, using date format yyyy-mm-dd.

This issue has multiple aspects:

• sqlglot doesn’t seem to allow quoted type names but they appear to be accepted by real-world DBMSs (this example works in TSQL; select '2022-09-27'::"date" works in Postgres)
• the parser for CONVERT() expects MySQL semantics (convert(value, type)), but TSQL inverts the order of parameters (convert(type, value))
• _parse_convert always produces exp.Cast, but the semantics of the example actually mean exp.StrToTime and exp.TimeToStr.

[tobymao]

given that convert can do weird stuff like money and xml styles, i think for tsql it needs to stay convert, but i don’t have the bandwidth to add this. again happy to help with a PR though.

[tobymao]

i’m not going to support quoted type names for now. although it may be legal, it’s quite strange. identifiers are used for finding columns and tables, using them for existing types doesn’t make much sense.

the convert has been implemented

parse_convert should produce a cast since it’s equivalent, strtotime and timetostr are the implicit implementations of varchar to date.