Which two statements are true regarding the COUNT function? (Choose two.)
A.
The COUNT function can be used only for CHAR, VARCHAR2, and NUMBER data types.
B.
COUNT(*) returns the number of rows including duplicate rows and rows containing NULL value in any of the columns.
C.
COUNT(cust_id) returns the number of rows including rows with duplicate customer IDs and NULL value in the CUST_ID column.
D.
COUNT(DISTINCT inv_amt)returns the number of rows excluding rows containing duplicates and NULL values in the INV_AMT column.
E.
A SELECT statement using the COUNT function with a DISTINCT keyword cannot have a WHERE clause.
WHy option C is wrong ?
The COUNT function has three formats:
COUNT(*)
COUNT(expr)
COUNT(DISTINCT expr)
COUNT(*) returns the number of rows in a table that satisfy the criteria of the SELECT statement, including duplicate rows and rows containing null values in any of the columns. If a WHERE clause is included in the SELECT statement, COUNT(*) returns the number of rows that satisfy the condition in the WHERE clause.
In contrast, COUNT(expr) returns the number of non-null values that are in the column identified by expr.
COUNT(DISTINCT expr) returns the number of unique, non-null values that are in the column identified by expr.
count(cust_id) does not return rows with NULL values in the column CUST_ID