COUNT and COUNT(Asterik) in Teradata

It will return the number of rows in a group.
Syntax:
COUNT ( { [ [ ALL | DISTINCT ] expression ] | * } )

ALL
Default.
Applicable to all values

DISTINCT
Applicable only for the unique values.

expression
Column expression.
text and image types are prohibited.

Example:
idNameSalary
1Roselin10000.0000
2Robert20000.0000
3Jobs10000.0000
4Jenifer40000.0000
5Joe10000.0000
6Sri10000.0000
7Josh90000.0000
8Naraine100000.0000
9Karthik10000.0000
10Atkinson100000.0000
10Raja15000.0000


SELECT COUNT(*) FROM tbl_employee
Output: 11

SELECT COUNT(ALL id) FROM tbl_employee
Output: 11

SELECT COUNT(DISTINCT id) FROM tbl_employee
Output: 10


Note:
COUNT(*) - All values including NULLs and duplicates
COUNT(ALL exp) - All values excluding NULLs
COUNT(DISTINCT exp) - Unique values