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±í TAB1 16,384 Ìõ¼Ç¼
±í TAB2 1 Ìõ¼Ç¼
Ñ¡ÔñTAB2×÷Ϊ»ù´¡±í (×îºÃµÄ·½·¨)
select count(*) from tab1,tab2 Ö´ÐÐʱ¼ä0.96Ãë
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select count(*) from tab2,tab1 Ö´ÐÐʱ¼ä26.09Ãë
Èç¹ûÓÐ3¸öÒÔÉϵıíÁ¬½Ó²éѯ, ÄǾÍÐèҪѡÔñ½»²æ±í(intersection table)×÷Ϊ»ù´¡±í, ½»²æ±íÊÇÖ¸ÄǸö±»ÆäËû±íËùÒýÓõıí.
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EMP±íÃèÊöÁËLOCATION±íºÍCATEGORY±íµÄ½»¼¯.
SELECT * from LOCATION L , CATEGORY C, EMP E
WHERE E.CAT_NO = C.CAT_NO AND E.LOCN = L.LOCN
AND E.EMP_NO BETWEEN 1000 AND 2000
½«±ÈÏÂÁÐSQL¸üÓÐЧÂÊ
SELECT E.CAT_NO from EMP E, LOCATION L , CATEGORY C
WHERE E.EMP_NO BETWEEN 1000 AND 2000
AND E.CAT_NO = C.CAT_NO AND E.LOCN = L.LOCN
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SELECT … from EMP E WHERE SAL > 50000 AND JOB = ‘MANAGER'
AND 25 < (SELECT COUNT(*) from EMP
WHERE MGR=E.EMPNO);
(¸ßЧ,Ö´ÐÐʱ¼ä10.6Ãë)
SELECT … from EMP E
WHERE 25 < (SELECT COUNT(*) from EMP WHERE MGR=E.EMPNO)
AND SAL > 50000
AND JOB = ‘MANAGER';
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