query_scalar!() { /* proc-macro */ }Expand description
Validated single-column query macro.
Syntax: query_scalar!(Type, "SQL") or query_scalar!(Type, "SQL", arg1, …)
Returns a [hyperdb_api::QueryScalar<Type>] builder. Type must implement
[hyperdb_api::RowValue]. No derive(Table) is required — scalars project
a single column and don’t map to a struct.
With the compile-time feature enabled, validates at build time that the
SQL returns exactly one column.