If it is necessary to retrieve only those transactions that specify elements for birth date, then the exists function is added to the where statement, as in Listing 10.
如果只能检索包含出生日期元素的交易，必须在where语句中使用exists函数，如清单10所示。
2
In general, children with low birth weight had poorer lung function, appetite and motor function than normal birth-weight children, as well as being more anxious, less positive and less lively.