A value of any SQL Server type, for code that handles columns and parameters whose types are only known at runtime: serving any table, copying rows between tables, a REPL.

Decoding: SqlValue is a FromSqlField that accepts any column (sqlValueDecoder), and SqlRow a whole row with its columns (sqlRowDecoder, sqlRowDecoderFor); queryMulti and callProcedure return every result set as SqlRows. A sql_variant decodes as its base type.

Encoding: SqlValue is a ToSqlField sent as the type its constructor names, so SELECT @p1 gives the same value back; SqlNull is an nvarchar(max) NULL, which the server converts to most types but not to binary or sql_variant.