Saturday, March 29, 2008

SQL Count Distinct

SQL Count Statement is used to count the total number of records saved in a particular table. SQL Count Statement returns total records including duplicates.

SQL Count (*) Statement does not take any other argument such bas column name to evaluate the result. It counts all columns whether they have duplicates or nulls.

E.g.:

USE NORTHWIND

SELECT COUNT (*) FROM ORDERS

Above SQL Query will return 830.


SQL Count (ALL [Column Name]) Statement returns the number of records including duplicates but excluding null value columns

E.g.:

SELECT COUNT (ALL CUSTOMERID) FROM ORDERS


SQL Count (DISTINCT [Column Name]) Statement returns unique, non null records.

E.g.:

SELECT COUNT (DISTINCT CUSTOMERID) FROM ORDERS

Above SQL Query will return 89.

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