While most types (e.g. boolean) are not valid key types for alternator users,
system tables derived from Scylla may still use this type for keys,
e.g. system_auth.roles. Note that types which are not directly
supported by alternator (e.g. double) will not be representable
out-of-the-box - instead, they simply fall back to string, which is both
human-readable and supported by alternator.
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