2019年8月版OCP 071认证考试原题-第35题

Posted 2020-11-22

choose two

Which two statenents are tue about the COUNT function?

A) It can only be used for NUMBER data types.

B) COUNT (DISTINCT inv_amt) returns the number of rows excluding rows containing dupicates and NULLs in the INV_AMT column

C) COUNT(*) returns the number of rows in a table including duplicate rows and rows containing NULLs in any column.

D) A SELECT statement using the COUNT function with a DISTINCT keyword cannot have a WHERE clause.

E) COUNT(inv_amt) returns the number of rows in a table including rows with NULL in the INV_AMT column.

Answer：：BC

(解析：count 对于 null 值是忽略的;可以与 where 一起使用。)