单项选择题
A subquery can be used to （）.
A. Create groups of data B. Sort data in a specific order C. Convert data to a different format D. Retrieve data based on an unknown condition
单项选择题 Which clause should you use to exclude group results? （）
单项选择题 What is true about joining tables through an equijoin? （）
单项选择题 You need to calculate the total of all salaries in the accounting department. Which group function should you use? （）
