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????2?????????????????????????????????????????????????????
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????1??LEFT JOIN??LEFT OUTER JOIN
??????????????????????? LEFT OUTER???????????????????校????????????????????????小?????????????????????????校????????????????????????????????斜??芯???????
????2??RIGHT JOIN ?? RIGHT OUTER JOIN
??????????????????????????????????????????????????小?????????????????????????校??????????????
????3??FULL JOIN ?? FULL OUTER JOIN
?????????????????????????械??????小??????????????????????????????????????????斜??邪??????????????????????校?????????????邪???????????????
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????-------------------------------------------------
????a?? id name  b?? id job parent_id
????1 ??3 1 23 1
????2 ???? 2 34 2
????3 ???? 3 34 4
????a.id?parent_id ??????
????--------------------------------------------------
????1?? ??????
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?????????
????1 ??3 1 23 1
????2 ???? 2 34 2
????2????????
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?????????
????1 ??3 1 23 1
????2 ???? 2 34 2
????3 ???? null
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?????????
????1 ??3 1 23 1
????2 ???? 2 34 2
????null 3 34 4
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?????????
????1 ??3 1 23 1
????2 ???? 2 34 2
????null ???? 3 34 4
????3 ???? null
???????????INNER JOIN??
???????????INNERJOIN?????????????????????????????????蟹??????????????????????????小?????谓??????????????????????纬???屑?????
???????纾�????????3?????4????????????
???????1?????????????????INNER JOIN???纬???屑??????????????????
????SELECTO.ID??O.ORDER_NUMBER??C.ID??C.NAME
????FROM CUSTOMERS C??ORDERS O
????WHERE C.ID=O.CUSTOMER_ID;
???????2????????????????????????????INNER JOIN???纬???屑????????????ON??????????????????
????SELECTO.ID??O.ORDER_NUMBER??C.ID??C.NAME
????FROM CUSTOMERS C INNER JOIN ORDERS O ON C.ID=O.CUSTOMER_ID;
???????????OUTER JOIN????
?????????????????????????????????????校???????????????????些?小?????????????????????LEFT OUTER JOIN?????????????RIGHT OUTER JOIN????????????FULL OUTER JOIN????
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????FROM ORDERS O LEFT OUTER JOIN CUSTOMERS C ON C.ID=O.CUSTOMER_ID;
???????4???????????RIGHT OUTER JOIN??
????SELECTO.ID??O.ORDER_NUMBER??O.CUSTOMER_ID??C.ID??C.NAME
????FROM ORDERS O RIGHT OUTER JOIN CUSTOMERS C ON C.ID=O.CUSTOMER_ID;
???????WHERE????????ON??????????????????????纾�
???????5??WHERE??????????
????SELECTO.ID??O.ORDER_NUMBER??O.CUSTOMER_ID??C.ID??C.NAME
????FROM ORDERS O LEFT OUTER JOIN CUSTOMERS C ON C.ID=O.CUSTOMER_ID
????WHERE O.ORDER_NUMBER<>'MIKE_ORDER001';
???????6???????5?械?WHERE???????ON???妾�
????SELECTO.ID??O.ORDER_NUMBER??O.CUSTOMER_ID??C.ID??C.NAME
????FROM ORDERS O LEFT OUTER JOIN CUSTOMERS C ONC.ID=O.CUSTOMER_ID AND O.ORDER_NUMBER<>'MIKE_ORDER001';
?????????5?????6????????????????????????????6???????????????????????????写???????????ON??????????????????????屑?????????????写??WHERE????小?
???????7??????????FULLOUTER JOIN????
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????FROM ORDERS O FULL OUTER JOIN CUSTOMERS C ON C.ID=O.CUSTOMER_ID;
???????MySQL?????????????????????????写?????Oracle??DB2?????????????????????????????????????????????
???????8???????????????????????????????7????????
????SELECTO.ID??O.ORDER_NUMBER??O.CUSTOMER_ID??C.ID??C.NAME
????FROM ORDERS O LEFT OUTER JOIN CUSTOMERS C ON C.ID=O.CUSTOMER_ID
????UNION
????SELECT O.ID??O.ORDER_NUMBER??O.CUSTOMER_ID??C.ID??C.NAME
????FROM ORDERS O RIGHT OUTER JOIN CUSTOMERS C ON C.ID=O.CUSTOMER_ID;
????SQL????????????????????????
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???????SQL?????????????SQL??????????????
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????FROM TAB1 T1
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????INNER JOIN TAB3 T3 ON (T1.C1=T2.C3)
????LEFT OUTER JOIN TAB4 ON(T2.C2=T3.C3);
????WHERE T1.X >T3.Y;
???????????SQL????????????????????
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