What are the various levels of Scheme data types we want to support, and how, for databases?
I drew on the R7RS-large docket to populate my Google sheet. I also made sure that it subsumes ISO 11404, a language-independent standard for data types, with the exception of enum types.
If anyone has a collection of the last drafts for the latest SQL standards, especially SQL:2016, I would appreciate copies so I don't have to hunt them down on the web.
I don't, but I found a couple of articles giving the standard data types of SQL 2011 and 2016.
Strings can be fixed-length, variable-length, or unbounded size (CLOBs). You can specify a per-column character set and independently a collation order, but neither the available charsets and collations nor their names are portable. There is a concept of NATIONAL CHAR vs plain CHAR types, but it is not even defined whether these are different encodings, never mind which encodings they are.
Bytevectors also can be fixed-length, variable-length, or unbounded size (BLOBs).
Exact numbers can be integers or fixed-point decimal fractions with a specified precision. (These may be floats under the covers, as in SQLite).
Inexact numbers can be IEEE binary32 or binary64.
Booleans.
Date/time types are DATE, TIME, and TIMESTAMP. The last two can have a precision (fractional seconds). All three can be with or without offsets from UTC. I have a *lot* of opinions about this group.
Time intervals are intervals of time with a start and an end. They are not the same as ISO 8601 periods, which are unanchored amounts of time.
Row types are used in SQL programming to represent the type of a single row. They can't exist inside a table.
Reference types are pointers to specific rows in specific tables. Evil, evil, evil!
Array types are for homogeneous arrays, a hack for getting around first normal form. Evil, evil!
Multiset types are another hack for getting around first normal form but unordered, unlike arrays. Evil, evil!
Decimal floats (SQL 2016 only). IEEE, but I have no information on which of 32-bit, 64-bit, and 128-bit formats are supported.