由于声明了 partno 字段惟一，因此重复上传同一个部件号将只用新记录替换旧索引记录。
Because the partno field is declared unique, repeated upload operations of the same part number merely replace the old index record with a new record.
由于大多数相机闪光灯在发出可见光同时就会发射出红外线，这一替换使得原型机能够发送并记录红外线。
Since most camera flashes emit IR along with their burst of visible light, the one substitution allowed the prototype to transmit and record infrared light.
在添加、替换或删除一个记录时，这两个值都会被更新。
Both values are updated whenever a record is added, replaced, or deleted.
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