我正在尝试在这里加入两个表，因此我根据postStatus获取特定用户的总行数。没有连接的数据是正确的，但是当我添加连接时，我得到了奇怪的结果。这是怎么回事？在这里使用什么是正确的联接？我需要返回两个表中的行（或null），即使其中一个中不存在userId。
**userData**
"postId" "userId" "postStatus" "checked" "postTitle"
"1" "1" "0" "0" "Title 1"
"2" "1" "0" "0" "Title 2"
"3" "1" "0" "0" "Title 3"
"4" "1" "0" "0" "Title 4"
"5" "1" "0" "0" "Title 5"
"6" "1" "1" "0" "Title 6"
"7" "1" "1" "0" "Title 7"
"8" "1" "6" "0" "Title 8"
"9" "1" "5" "0" "Title 9"
"10" "1" "5" "0" "Title 10"
"11" "2" "0" "0" "Title 1"
"12" "2" "0" "0" "Title 2"
"13" "2" "1" "0" "Title 3"
**userDataMod**
"postId" "userId" "postStatus" "checked" "postTitle"
"1" "1" "10" "0" "Title 11"
"2" "1" "10" "0" "Title 12"
"3" "2" "0" "0" "Title 4"
带连接的SQL
select
a.userId,
sum(a.postStatus = 0) published,
sum(a.postStatus = 1) inactive,
sum(a.postStatus = 5) recalled,
sum(a.postStatus = 6) deleted,
sum(b.postStatus = 10) unChecked
from userData a join userdatamod b on a.userId = b.userId where a.userId = 1;
// what is the correct join to use here that'll return data (null) from both tables
// even when a userId may not be present in one of them?
结果不正确（请参阅下面的结果。这些是正确的结果）
"userId" "published" "inactive" "recalled" "deleted" "unChecked"
"1" "10" "4" "4" "2" "20"
没有连接的Sql可以提供正确的结果
select
a.userId,
sum(a.postStatus = 0) published,
sum(a.postStatus = 1) inactive,
sum(a.postStatus = 5) recalled,
sum(a.postStatus = 6) deleted
from userData a where a.userId = 1;
不使用加入时的正确结果
"userId" "published" "inactive" "recalled" "deleted"
"1" "5" "2" "2" "1"
//Note: there are 5 rows with postStatus 0 in userData, and 2 with postStaus = 1 and
1 with postsStaus = 6 and so on for userId = 1
正确的方法是什么？
使用加入时的预期结果
"userId" "published" "inactive" "recalled" "deleted" "unChecked"
"1" "5" "2" "2" "1" "2"
//unChecked = the 2 rows from userDataMod with postStatus = 10 for useId = 1
延
"postId" "userId" "postStatus" "checked" "postTitle" "postId" "userId" "postStatus" "checked" "postTitle"
"1" "1" "0" "0" "Title 1" "1" "1" "10" "0" "Title 1"
"1" "1" "0" "0" "Title 1" "2" "1" "10" "0" "Title 2"
"2" "1" "0" "0" "Title 2" "1" "1" "10" "0" "Title 1"
"2" "1" "0" "0" "Title 2" "2" "1" "10" "0" "Title 2"
"3" "1" "0" "0" "Title 3" "1" "1" "10" "0" "Title 1"
"3" "1" "0" "0" "Title 3" "2" "1" "10" "0" "Title 2"
"4" "1" "0" "0" "Title 4" "1" "1" "10" "0" "Title 1"
"4" "1" "0" "0" "Title 4" "2" "1" "10" "0" "Title 2"
"5" "1" "0" "0" "Title 5" "1" "1" "10" "0" "Title 1"
"5" "1" "0" "0" "Title 5" "2" "1" "10" "0" "Title 2"
"6" "1" "1" "0" "Title 6" "1" "1" "10" "0" "Title 1"
"6" "1" "1" "0" "Title 6" "2" "1" "10" "0" "Title 2"
"7" "1" "1" "0" "Title 7" "1" "1" "10" "0" "Title 1"
"7" "1" "1" "0" "Title 7" "2" "1" "10" "0" "Title 2"
"8" "1" "6" "0" "Title 8" "1" "1" "10" "0" "Title 1"
"8" "1" "6" "0" "Title 8" "2" "1" "10" "0" "Title 2"
"9" "1" "5" "0" "Title 9" "1" "1" "10" "0" "Title 1"
"9" "1" "5" "0" "Title 9" "2" "1" "10" "0" "Title 2"
"10" "1" "5" "0" "Title 10" "1" "1" "10" "0" "Title 1"
"10" "1" "5" "0" "Title 10" "2" "1" "10" "0" "Title 2"
的UserData
CREATE TABLE `userdata` (
`postId` INT(10) NOT NULL AUTO_INCREMENT,
`userId` INT(10) NULL DEFAULT '0',
`postStatus` INT(10) NULL DEFAULT '0',
`checked` INT(10) NULL DEFAULT '0',
`postTitle` VARCHAR(50) NULL DEFAULT '0',
PRIMARY KEY (`postId`)
)
COLLATE='utf8_general_ci'
ENGINE=MyISAM
AUTO_INCREMENT=14;
userDataMod
CREATE TABLE `userdatamod` (
`postId` INT(10) NOT NULL AUTO_INCREMENT,
`userId` INT(10) NULL DEFAULT '0',
`postStatus` INT(10) NULL DEFAULT '0',
`checked` INT(10) NULL DEFAULT '0',
`postTitle` VARCHAR(50) NULL DEFAULT '0',
PRIMARY KEY (`postId`)
)
COLLATE='utf8_general_ci'
ENGINE=MyISAM
ROW_FORMAT=DYNAMIC
AUTO_INCREMENT=4;
答案 0 :(得分：0)
我认为你必须与userid和postId
select
a.userId,
sum(a.postStatus = 0) published,
sum(a.postStatus = 1) inactive,
sum(a.postStatus = 5) recalled,
sum(a.postStatus = 6) deleted,
sum(b.postStatus = 10) unChecked
from userData a join userdatamod b on a.userId = b.userId and a.postId=b.postId where a.userId = 1;
答案 1 :(得分：0)
另一种可能的解决方案：
select
a.userId,
sum(a.postStatus = 0) published,
sum(a.postStatus = 1) inactive,
sum(a.postStatus = 5) recalled,
sum(a.postStatus = 6) deleted,
b.unChecked
from userData a left outer join
(select userId, sum(poststatus = 10) unChecked
from userDataMod
group by userId)
b on a.userId = b.userId
where a.userId = 1;