本文探讨了在处理特定数据库查询任务时使用子查询和连接的重要性。通过具体例子，如查找信用限额相同的客户、比较城市间的平均信用限额等，展示了如何有效地利用SQL进行复杂的数据筛选。
Q58. View the exhibit and examine the structure of the CUSTOMERS table.
Which two tasks would require subqueries or joins to be executed in a single statement?
A. listing of customers who do not have a credit limit and were born before 1980
B. finding the number of customers, in each city, who’s marital status is ‘married’.
C. finding the average credit limit of male customers residing in ‘Tokyo’ or ‘Sydney’
D. listing of those customers, whose credit limit is the same as the credit limit of customers residing in the city ‘Tokyo’.
E. finding the number of customers, in each city, whose credit limit is more than the average credit limit of all the customers
Correct Answer: dE
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