做一个课程表。
Too many columns in a table can make the scan time for queries much longer than if there are just a few columns.
一个表中有太多列比仅有一些列时进行查询所需的扫描时间要长。
The complex table layout also increased the time required to determine where to make a change or add content.
复杂的表布局还增加了确定在何处做更改或添加内容所需的时间。
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