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mysql²Ù×÷ Left join , Right Join, Inner Join


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Table A
aid   adate
1      a1
2      a2
3      a3
TableB
bid bdate
1    b1
2   b2
4    b4
Á½¸ö±ía,bÏàÁ¬½Ó,Ҫȡ³öidÏàͬµÄ×Ö¶Î
select * from a inner join
b on a.aid = b.bidÕâÊǽöÈ¡³öÆ¥ÅäµÄÊý¾Ý.
´ËʱµÄÈ¡³öµÄÊÇ:
1 a1 b1
2 a2 b2
ÄÇôleft join Ö¸:
select * from a left join
b on
a.aid = b.bid
È¡³öa±íËùÓÐÊý¾Ý,ÄÃbµÄÊý¾ÝÓëa±È½Ï,ÏàͬµÄÈ¡³ö,²»Í¬µÄbÈ¡¿Õֵȡ³ö
´ËʱµÄÈ¡³öµÄÊÇ:
1 a1 b1
2 a2 b2
3 a3 ¿Õ×Ö·û
ͬÑùµÄÒ²ÓÐright join
 
select * from a right join
b on
a.aid = b.bid
È¡³öb±íËùÓÐÊý¾Ý,ÄÃaµÄÊý¾ÝÓëb±È½Ï,ÏàͬµÄÈ¡³ö,²»Í¬µÄaÈ¡¿Õֵȡ³ö
´ËʱµÄÈ¡³öµÄÊÇ:
1 a1 b1
2 a2 b2
4 ¿Õ×Ö·û b4
×¢:
¶¼ÊÇÔÚonµÄÌõ¼þÏÂ
¶þ. left join/right join/inner join²Ù×÷ÑÝʾ
±íA¼Ç¼ÈçÏ£º
aID        aNum
1           a20050111
2           a20050112
3           a20050113
4          a20050114
5           a20050115
±íB¼Ç¼ÈçÏÂ:
bID        bName
1            2006032401
2            2006032402
3           2006032403
4           2006032404
8           2006032408
ʵÑéÈçÏÂ:
1.    left join
sqlÓï¾äÈçÏÂ:
SELECT

*

from
A
LEFT

JOIN
B
ON
A.aID
=
B.bID
½á¹ûÈçÏÂ:
aID        aNum     &


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