COUNTã?¯å¼?ã?®è¡Œæ•°ã‚’æ•°ã?ˆã‚‹é›†ç´„関数ã?§ã?™ã€‚(集約 (集å?ˆé–¢æ•°)ã‚’å?‚ç…§ã?—ã?¦ã??ã? ã?•ã?„。) COUNTã?¯ã?©ã?®ã‚ˆã?†ã?ªåž‹ã?®å¼?ã?§ã‚‚利用ã?§ã??ã?¾ã?™ã€‚
COUNT ( [ DISTINCT | ALL ] å¼? )
DISTINCTã?¨ã?„ã?†é™?定詞ã?«ã‚ˆã‚Šé‡?複をå?–り除ã??ã?“ã?¨ã?Œã?§ã??ã?¾ã?™ã€‚ALLã?¨ã?„ã?†é™?定詞ã?«ã‚ˆã‚Šé‡?複をã??ã?®ã?¾ã?¾ã?«ã?™ã‚‹ã?“ã?¨ã?Œã?§ã??ã?¾ã?™ã€‚ã‚‚ã?—DISTINCTã‚‚ALLも指定ã?•れã?ªã?‘れã?°ã€?ALLã?Œä¸Žã?ˆã‚‰ã‚Œã?Ÿã‚‚ã?®ã?¨ã?—ã?¾ã?™ã€‚例ã?ˆã?°ã€?列ã?«1ã€?1ã€?1ã€?1ã?Šã‚ˆã?³2ã?¨ã?„ã?†å€¤ã?Œã?‚ã?£ã?Ÿå ´å?ˆã€?COUNT(col)ã?¯COUNT(DISTINCT col)より大ã??ã?ªæ•°ã‚’è¿”ã?—ã?¾ã?™ã€‚
一ã?¤ã?®é?¸æŠžå¼?ã?«ã?¯ã€?唯一ã?¤ã?®DISTINCT集約å¼?ã‚’ã?¨ã‚‹ã?“ã?¨ã?Œã?§ã??ã?¾ã?™ã€‚例ã?ˆã?°æ¬¡ã?®ã‚ˆã?†ã?«å•?å?ˆã?›ã‚‹äº‹ã?¯ã?§ã??ã?¾ã?›ã‚“。
-- å•?ã?„å?ˆã‚?ã?›ã?§ã??ã?ªã?„
SELECT COUNT (DISTINCT flying_time), SUM (DISTINCT miles)
FROM Flights
å¼?ã?«ã?¯è¤‡æ•°ã?®åˆ—ã?¸ã?®å?‚ç…§ã‚„å¼?ã‚’ç½®ã??事ã?Œã?§ã??ã?¾ã?™ã?Œã€?ä»–ã?®é›†ç´„や副å•?å?ˆã?›ã‚’ç½®ã??ã?“ã?¨ã?¯ã?§ã??ã?¾ã?›ã‚“。 ã‚‚ã?—å¼?ã?ŒNULLã?¨è©•価ã?•ã‚Œã‚‹å ´å?ˆã€?ã??ã?®è©•価値ã?«ã?¤ã?„ã?¦é›†ç´„ã?¯è¡Œã‚?れã?¾ã?›ã‚“。
COUNT�よる�果�データ型��INTEGER��。
-- ã??れã?žã‚Œã?®åœ°åŸŸã?®å›½ã?®æ•°ã‚’æ•°ã?ˆã€?
-- 二国以上�る地域を表示�る。
SELECT COUNT (country), region
FROM Countries
GROUP BY region
HAVING COUNT (country) > 1