If updates to the coordinate columns are possible, you may still be able to avoid bulk copies if the source table contains a time stamp column that records the time of last update for each row.
如果可能更新坐标列，但是源表包含一个时间戳列，其中记录了每行最后一次更新的时间，那么仍然可以避免批量复制。
Inspection of the error table conveniently reveals the source row as well as the problematic coordinate.
检查错误表就能够方便地查明源表行以及出问题的坐标。
When either of the coordinate columns in the source table is updated, a new point geometry must be constructed. The update trigger looks like this
当更新源表中的坐标列时，必须构造一个新的点几何值。
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