The optimizer normally chooses a table scan if no appropriate index has been created or if an index scan would be more costly.

如果没有创建合适的索引，或者如果索引扫描的成本更高一些，优化器通常就选择表扫描。

youdao

Diagnosis may later involve an MRI scan if a tear in the hip cartilage is suspected, but this can be difficult to ascertain.

随后的诊断包括核磁共振，如果怀疑髋关节软骨撕裂，但是很难确诊。

youdao

On a subsequent scan, if a newly computed checksum is different from the previously generated checksum, the page is changing and is therefore not a good candidate for merging.

在一次后续扫描中，如果新计算的校验和不等于此前计算的校验和，则该页面正在更改，因此不是一个合格的合并候选对象。

youdao

The researchers have developed rules to predict if a head injury is serious enough for a scan.

VOA: special.2009.10.28

People with mild memory loss will get a brain scan to see if plaques are present.

FORBES: Magazine Article

If you scan any footballer at any time, you will find something wrong with them.

BBC: Robbie Keane to be sidelined at West Ham for month

But if you scan the world for the positive, you start to reap an amazing advantage.

CNN: Is happiness the secret of success?