错误的坐标表现为缺少相关联的点几何值，触发器过程会悄悄地终止。

Bad coordinates are reflected in the absence of associated point geometry values, and the trigger procedures fail silently.

youdao

内部调用（对 ST_Point()）创建一个具有纬度-经度坐标（SRID = 1）的点几何值。

The inner call, to ST_Point(), creates a point geometry with latitude-longitude coordinates (SRID = 1).

youdao

当更新源表中的坐标列时，必须构造一个新的点几何值。

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

youdao

So here's the example I'm going to start with.

做二维几何的程序,关于平面上的点。

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