\u5185\u90e8\u8fde\u63a5 inner join \u4e24\u8868\u90fd\u6ee1\u8db3\u7684\u7ec4\u5408
\nfull outer \u5168\u8fde \u4e24\u8868\u76f8\u540c\u7684\u7ec4\u5408\u5728\u4e00\u8d77\uff0cA\u8868\u6709\uff0cB\u8868\u6ca1\u6709\u7684\u6570\u636e\uff08\u663e\u793a\u4e3anull\uff09,\u540c\u6837B\u8868\u6709
\nA\u8868\u6ca1\u6709\u7684\u663e\u793a\u4e3a(null)
\nA\u8868 left join B\u8868 \u5de6\u8fde,\u4ee5A\u8868\u4e3a\u57fa\u7840\uff0cA\u8868\u7684\u5168\u90e8\u6570\u636e\uff0cB\u8868\u6709\u7684\u7ec4\u5408\u3002\u6ca1\u6709\u7684\u4e3anull
\nA\u8868 right join B\u8868 \u53f3\u8fde,\u4ee5B\u8868\u4e3a\u57fa\u7840\uff0cB\u8868\u7684\u5168\u90e8\u6570\u636e\uff0cA\u8868\u7684\u6709\u7684\u7ec4\u5408\u3002\u6ca1\u6709\u7684\u4e3anull
\n\u67e5\u8be2\u5206\u6790\u5668\u4e2d\u6267\u884c\uff1a
\n–\u5efa\u8868table1,table2\uff1a
\ncreate table table1(id int,name varchar(10))
\ncreate table table2(id int,score int)
\ninsert into table1 select 1,’lee’
\ninsert into table1 select 2,’zhang’
\ninsert into table1 select 4,’wang’
\ninsert into table2 select 1,90
\ninsert into table2 select 2,100
\ninsert into table2 select 3,70
\n\u5982\u8868
\n————————————————-
\ntable1|table2|
\n————————————————-
\nidname|idscore|
\n1lee|190|
\n2zhang|2100|
\n4wang|370|
\n————————————————-<\/p>\n
\u4ee5\u4e0b\u5747\u5728\u67e5\u8be2\u5206\u6790\u5668\u4e2d\u6267\u884c<\/p>\n
\u4e00\u3001\u5916\u8fde\u63a5
\n1.\u6982\u5ff5\uff1a\u5305\u62ec\u5de6\u5411\u5916\u8054\u63a5\u3001\u53f3\u5411\u5916\u8054\u63a5\u6216\u5b8c\u6574\u5916\u90e8\u8054\u63a5<\/p>\n
2.\u5de6\u8fde\u63a5\uff1aleft join \u6216 left outer join
\n(1)\u5de6\u5411\u5916\u8054\u63a5\u7684\u7ed3\u679c\u96c6\u5305\u62ec LEFT OUTER \u5b50\u53e5\u4e2d\u6307\u5b9a\u7684\u5de6\u8868\u7684\u6240\u6709\u884c\uff0c\u800c\u4e0d\u4ec5\u4ec5\u662f\u8054\u63a5\u5217\u6240\u5339\u914d\u7684\u884c\u3002\u5982\u679c\u5de6\u8868\u7684\u67d0\u884c\u5728\u53f3\u8868\u4e2d\u6ca1\u6709\u5339\u914d\u884c\uff0c\u5219\u5728\u76f8\u5173\u8054\u7684\u7ed3\u679c\u96c6\u884c\u4e2d\u53f3\u8868\u7684\u6240\u6709\u9009\u62e9\u5217\u8868\u5217\u5747\u4e3a\u7a7a\u503c(null)\u3002
\n(2)sql \u8bed\u53e5
\nselect * from table1 left join table2 on table1.id=table2.id
\n————-\u7ed3\u679c————-
\nidnameidscore
\n——————————
\n1lee190
\n2zhang2100
\n4wangNULLNULL
\n——————————
\n\u6ce8\u91ca\uff1a\u5305\u542btable1\u7684\u6240\u6709\u5b50\u53e5\uff0c\u6839\u636e\u6307\u5b9a\u6761\u4ef6\u8fd4\u56detable2\u76f8\u5e94\u7684\u5b57\u6bb5\uff0c\u4e0d\u7b26\u5408\u7684\u4ee5null\u663e\u793a<\/p>\n
3.\u53f3\u8fde\u63a5\uff1aright join \u6216 right outer join
\n(1)\u53f3\u5411\u5916\u8054\u63a5\u662f\u5de6\u5411\u5916\u8054\u63a5\u7684\u53cd\u5411\u8054\u63a5\u3002\u5c06\u8fd4\u56de\u53f3\u8868\u7684\u6240\u6709\u884c\u3002\u5982\u679c\u53f3\u8868\u7684\u67d0\u884c\u5728\u5de6\u8868\u4e2d\u6ca1\u6709\u5339\u914d\u884c\uff0c\u5219\u5c06\u4e3a\u5de6\u8868\u8fd4\u56de\u7a7a\u503c\u3002
\n(2)sql \u8bed\u53e5
\nselect * from table1 right join table2 on table1.id=table2.id
\n————-\u7ed3\u679c————-
\nidnameidscore
\n——————————
\n1lee190
\n2zhang2100
\nNULLNULL370
\n——————————
\n\u6ce8\u91ca\uff1a\u5305\u542btable2\u7684\u6240\u6709\u5b50\u53e5\uff0c\u6839\u636e\u6307\u5b9a\u6761\u4ef6\u8fd4\u56detable1\u76f8\u5e94\u7684\u5b57\u6bb5\uff0c\u4e0d\u7b26\u5408\u7684\u4ee5null\u663e\u793a<\/p>\n
4.\u5b8c\u6574\u5916\u90e8\u8054\u63a5:full join \u6216 full outer join
\n(1)\u5b8c\u6574\u5916\u90e8\u8054\u63a5\u8fd4\u56de\u5de6\u8868\u548c\u53f3\u8868\u4e2d\u7684\u6240\u6709\u884c\u3002\u5f53\u67d0\u884c\u5728\u53e6\u4e00\u4e2a\u8868\u4e2d\u6ca1\u6709\u5339\u914d\u884c\u65f6\uff0c\u5219\u53e6\u4e00\u4e2a\u8868\u7684\u9009\u62e9\u5217\u8868\u5217\u5305\u542b\u7a7a\u503c\u3002\u5982\u679c\u8868\u4e4b\u95f4\u6709\u5339\u914d\u884c\uff0c\u5219\u6574\u4e2a\u7ed3\u679c\u96c6\u884c\u5305\u542b\u57fa\u8868\u7684\u6570\u636e\u503c\u3002
\n(2)sql \u8bed\u53e5
\nselect * from table1 full join table2 on table1.id=table2.id
\n————-\u7ed3\u679c————-
\nidnameidscore
\n——————————
\n1lee190
\n2zhang2100
\n4wangNULLNULL
\nNULLNULL370
\n——————————
\n\u6ce8\u91ca\uff1a\u8fd4\u56de\u5de6\u53f3\u8fde\u63a5\u7684\u548c\uff08\u89c1\u4e0a\u5de6\u3001\u53f3\u8fde\u63a5\uff09<\/p>\n
\u4e8c\u3001\u5185\u8fde\u63a5
\n1.\u6982\u5ff5\uff1a\u5185\u8054\u63a5\u662f\u7528\u6bd4\u8f83\u8fd0\u7b97\u7b26\u6bd4\u8f83\u8981\u8054\u63a5\u5217\u7684\u503c\u7684\u8054\u63a5<\/p>\n
2.\u5185\u8fde\u63a5\uff1ajoin \u6216 inner join<\/p>\n
3.sql \u8bed\u53e5
\nselect * from table1 join table2 on table1.id=table2.id
\n————-\u7ed3\u679c————-
\nidnameidscore
\n——————————
\n1lee190
\n2zhang2100
\n——————————
\n\u6ce8\u91ca\uff1a\u53ea\u8fd4\u56de\u7b26\u5408\u6761\u4ef6\u7684table1\u548ctable2\u7684\u5217<\/p>\n
4.\u7b49\u4ef7\uff08\u4e0e\u4e0b\u5217\u6267\u884c\u6548\u679c\u76f8\u540c\uff09
\nA:select a.*,b.* from table1 a,table2 b where a.id=b.id
\nB:select * from table1 cross join table2 where table1.id=table2.id (\u6ce8\uff1across join\u540e\u52a0\u6761\u4ef6\u53ea\u80fd\u7528where,\u4e0d\u80fd\u7528on)<\/p>\n
\u4e09\u3001\u4ea4\u53c9\u8fde\u63a5(\u5b8c\u5168)<\/p>\n
1.\u6982\u5ff5\uff1a\u6ca1\u6709 WHERE \u5b50\u53e5\u7684\u4ea4\u53c9\u8054\u63a5\u5c06\u4ea7\u751f\u8054\u63a5\u6240\u6d89\u53ca\u7684\u8868\u7684\u7b1b\u5361\u5c14\u79ef\u3002\u7b2c\u4e00\u4e2a\u8868\u7684\u884c\u6570\u4e58\u4ee5\u7b2c\u4e8c\u4e2a\u8868\u7684\u884c\u6570\u7b49\u4e8e\u7b1b\u5361\u5c14\u79ef\u7ed3\u679c\u96c6\u7684\u5927\u5c0f\u3002\uff08table1\u548ctable2\u4ea4\u53c9\u8fde\u63a5\u4ea7\u751f3*3=9\u6761\u8bb0\u5f55\uff09<\/p>\n
2.\u4ea4\u53c9\u8fde\u63a5\uff1across join (\u4e0d\u5e26\u6761\u4ef6where…)<\/p>\n
3.sql\u8bed\u53e5
\nselect * from table1 cross join table2
\n————-\u7ed3\u679c————-
\nidnameidscore
\n——————————
\n1lee190
\n2zhang190
\n4wang190
\n1lee2100
\n2zhang2100
\n4wang2100
\n1lee370
\n2zhang370
\n4wang370
\n——————————
\n\u6ce8\u91ca\uff1a\u8fd4\u56de3*3=9\u6761\u8bb0\u5f55\uff0c\u5373\u7b1b\u5361\u5c14\u79ef<\/p>\n
4.\u7b49\u4ef7\uff08\u4e0e\u4e0b\u5217\u6267\u884c\u6548\u679c\u76f8\u540c\uff09
\nA:select * from table1,table2<\/p>\n","protected":false},"excerpt":{"rendered":"
\u5185\u90e8\u8fde\u63a5 inner join \u4e24\u8868\u90fd\u6ee1\u8db3\u7684\u7ec4\u5408 full outer \u5168\u8fde \u4e24\u8868\u76f8\u540c\u7684\u7ec4\u5408\u5728\u4e00\u8d77\uff0cA\u8868\u6709\uff0cB\u8868\u6ca1\u6709\u7684\u6570\u636e\uff08\u663e\u793a\u4e3anull\uff09,\u540c\u6837B\u8868\u6709 A\u8868\u6ca1\u6709\u7684\u663e\u793a\u4e3a(null) A\u8868 left join B\u8868 \u5de6\u8fde,\u4ee5A\u8868\u4e3a\u57fa\u7840\uff0cA\u8868\u7684\u5168\u90e8\u6570\u636e\uff0cB\u8868\u6709\u7684\u7ec4\u5408\u3002\u6ca1\u6709\u7684\u4e3anull A\u8868 right join B\u8868 \u53f3\u8fde,\u4ee5B\u8868\u4e3a\u57fa\u7840\uff0cB\u8868\u7684\u5168\u90e8\u6570\u636e\uff0cA\u8868\u7684\u6709\u7684\u7ec4\u5408\u3002\u6ca1\u6709\u7684\u4e3anull \u67e5\u8be2\u5206\u6790\u5668\u4e2d\u6267\u884c\uff1a –\u5efa\u8868table1,table2\uff1a create table table1(id int,name varchar(10)) create table table2(id int,score int) insert into table1 select 1,’lee’ insert into table1 select 2,’zhang’ insert into table1 select 4,’wang’ insert into table2 select 1,90 insert into table2 select […]<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[],"class_list":["post-3129","post","type-post","status-publish","format-standard","hentry","category-life"],"_links":{"self":[{"href":"https:\/\/jpuyy.com\/index.php?rest_route=\/wp\/v2\/posts\/3129","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/jpuyy.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/jpuyy.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/jpuyy.com\/index.php?rest_route=\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/jpuyy.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=3129"}],"version-history":[{"count":2,"href":"https:\/\/jpuyy.com\/index.php?rest_route=\/wp\/v2\/posts\/3129\/revisions"}],"predecessor-version":[{"id":3660,"href":"https:\/\/jpuyy.com\/index.php?rest_route=\/wp\/v2\/posts\/3129\/revisions\/3660"}],"wp:attachment":[{"href":"https:\/\/jpuyy.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=3129"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/jpuyy.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=3129"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/jpuyy.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=3129"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}