嵌套子查询的外部查询工作原理测验
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Questions and Answers

以下哪个说法是最正确的？

  • 内查询也称为子查询 (correct)
  • 内查询只能用于SELECT语句
  • 内查询只能用于INSERT语句
  • 内查询不能用作列表达式

以下哪个语句可以使用内查询？

  • INSERT
  • DELETE
  • UPDATE
  • SELECT (correct)

内查询可以用作列表达式吗？

  • 只能在FROM子句中使用
  • 只能在WHERE子句中使用
  • 不可以
  • 可以 (correct)

在SQL中，嵌套子查询的执行顺序是什么？

<p>从最内层子查询开始，然后依次执行外层子查询 (D)</p> Signup and view all the answers

在SQL中，嵌套子查询是什么类型的语句？

<p>SELECT语句 (C)</p> Signup and view all the answers

嵌套子查询可以嵌套多少层？

<p>没有限制 (D)</p> Signup and view all the answers

以下哪个是最正确的？

<p>在Oracle 11g Express Edition中执行的代码是什么？ (A)</p> Signup and view all the answers

以下哪个是最正确的？

<p>嵌套子查询返回的是什么？ (D)</p> Signup and view all the answers

以下哪个是最正确的？

<p>子查询返回了哪些job_id？ (D)</p> Signup and view all the answers

以下哪个是最正确的？

<p>内部查询返回职位ID，员工的平均工资，这些员工的平均工资小于前一个查询返回的最低工资的平均值 (D)</p> Signup and view all the answers

根据给定的代码，以下哪个描述最准确？

<p>内部查询返回代理商表中佣金小于0.12%的行 (B)</p> Signup and view all the answers

根据给定的代码，以下哪个描述最准确？

<p>外部查询返回订单表中订单金额大于2000且订单日期在'01-sep-08'之前的订单的ord_num，ord_date，ord_amount和advance_amount (D)</p> Signup and view all the answers

Which query is executed first in a nested subquery?

<p>The nested subquery (B)</p> Signup and view all the answers

What does the nested subquery in the example retrieve?

<p>Unique job_ids from the job_history table (C)</p> Signup and view all the answers

What does the subquery in the example return?

<p>Maximum of averages of min_salary for each unique job_id (D)</p> Signup and view all the answers

Which SQL statement can contain a subquery?

<p>SELECT (C)</p> Signup and view all the answers

What is the purpose of a subquery in SQL?

<p>To perform a SELECT query within another query (D)</p> Signup and view all the answers

Which operator can be used with a subquery in SQL?

<p>= (D)</p> Signup and view all the answers

In SQL, a subquery can be used as a column expression. What does this mean?

<p>The subquery can be used to retrieve data for a specific column in the outer query (C)</p> Signup and view all the answers
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