近来，随着债券边际收益率的提高，几家华尔街银行对潜在的借贷成本临界点发出警告。
As bond yields edged higher recently, several Wall Street Banks issued warnings about potentially crippling debt-service costs.
对于其它大一些的字段来说，就会更容易看到空间收益，例如，datetime列的临界值是只要达到52%的行值为null就划算。
For larger fields the gains are seen much earlier, for example the critical point for datetime columns is only 52% of the rows.
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