The next two queries cannot use an index because an element "phone408" needs to be returned for every author, even if it is an empty element for authors outside the 408 area code.

下面两个查询不能使用索引，因为必须为每个author返回元素“phone408”，即使是区号408之外的author的空元素。

youdao

Spain ruled this large area including New Orleans until 1800, when the whole area was again returned to France, only to be sold to the United States in 1803.

西班牙便统治了这块包含新奥尔良在内的广大土地，一直到1800年，这时西班牙才又把整个区域归还给法国，不过在1803年却又卖给了美国。

youdao

The building will use solar energy to heat the pools and the interior area, and all backwash water is to be filtered and returned to the swimming pools.

建筑将采用太阳能加热游泳池和室内面积，而所有反冲洗水是经过过滤和回到泳池。

youdao

Stagecoach said services had returned to normal, but the speed restriction would be in place around the area of the accident until repairs could be carried out.

BBC: Cambridgeshire guided bus crash damages tracks