1z0-071 Oracle Database 12c SQL 第48题 GROUP BY

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最新推荐文章于 2019-11-25 17:03:54 发布

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分类专栏：数据库：Oracle DBA成长之路文章标签： 1z0-071 ocp oracle 11g oracle 12c

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本文详细解析了 SQL 语句中 GROUP BY 子句的使用方法及其注意事项。介绍了 GROUP BY 子句通常与聚合函数搭配使用，用于对数据进行分组处理，并解释了在 SELECT 语句中如何正确使用 GROUP BY 子句。

Q48. Which two statements are true regarding the GROUP BY clause in a SQL statement? (Choose two.)
A. You can use column alias in the GROUP BY clause.
B. Using the WHERE clause after the GROUP BY clause excludes the rows after creating groups.
C. The GROUP BY clause is mandatory if you are using an aggregate function in the SELECT clause.
D. Using the WHERE clause before the GROUP BY clause excludes the rows before creating groups.

E. If the SELECT clause has an aggregate function, then those individual columns without an aggregate function in theSELECT clause should be included in the GROUP BY cause.

Correct Answer: DE

【注意】分组group by一般与聚合函数连用，即先分组再聚合（如先分组再求和、先分组再求平均等等）。group by如果只是对行进行单独的分组使用，那么使用意义不大。在复杂的SQL查询中Group by子句大多数时候与聚合函数一起出现。