Avanceret SQL i mysql_query() virker ikke?

Hvorfor virker dette i PHPMyAdmin men ikke i mit eget PHP script?

---------------------------
SET @acount = 0;

SELECT @account := COUNT( * )
FROM files
WHERE accountid = '1';

UPDATE statsinfo SET files = @account WHERE accountid = '1';
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Fejlen jeg får fra mit script:

You have an error in your SQL syntax near ';

SELECT @account := COUNT( * )
FROM files
WHERE accountid = '1';

UPDATE' at line 1