Luke L (7/27/2010)

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Nope, run the code you get 7 and 8 respectively. The Distinct in the second query is applied after the rows are created. So since there is no group by clause it counts all of the userid's and returns 1 row. The DISTINCT in that instance makes sure there are distinct rows, which there are because there is only one. So Yes the DISTINCT keyword doesn't really do anything in the second select, but that was more or less the point of the example that bitbucket gave, to illustrate the difference between Count(DISTINCT expression ) and SELECT DISTINCT count(expression).

-Luke.

Carlo Romagnano (7/27/2010)

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That's false: COUNT(*) returns the number of ROWS regardless of of columns.

Explanation: The distinct clause guarantees all output records will be unique, irrespective of how you write the select statement.

 
CREATE TABLE TABLE2(
	Col1 int
	,Col2 int)

INSERT INTO table2 VALUES(1,3)
INSERT INTO table2 VALUES(1,4)

SELECT DISTINCT Col1,Col2 FROM table2

$partacu$ (8/2/2010)

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But while using 2 columns with DISTINCT can produce non unique rows (ateleast in one columm...)