MySQL计数，左连接，分组返回零行

在下面的sql语句中：

 SELECT `keywords`.keyID, count(`keywords-occurencies`.keyID) as countOccurencies 
                    FROM `keywords-occurencies`  
                    LEFT JOIN `keywords` 
                    ON `keywords-occurencies`.keyID = `keywords`.keyID 
                    WHERE `keywords-occurencies`.`keyID` IN (1,2,3) AND date BETWEEN '2013/01/25' AND '2013/01/27'
                    GROUP BY `keywords`.`keyID`

如果keyID 3没有返回值，则不会将其计为0，也不会包含在结果集中，并显示类似的结果

keyID countOccurencies
1       3
3       5

我想以如下方式显示零结果

keyID countOccurencies
1       3
2       0
3       5

要测试的样本数据：

--
-- Table structure for table `keywords`
--

CREATE TABLE IF NOT EXISTS `keywords` (
  `keyID` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `keyName` varchar(40) NOT NULL,
  PRIMARY KEY (`keyID`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=3 ;

--
-- Dumping data for table `keywords`
--

INSERT INTO `keywords` (`keyID`, `keyName`) VALUES
(1, 'testKey1'),
(2, 'testKey2');

-- --------------------------------------------------------

--
-- Table structure for table `keywords-occurencies`
--

CREATE TABLE IF NOT EXISTS `keywords-occurencies` (
  `occurencyID` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `keyID` int(10) unsigned NOT NULL,
  `date` date NOT NULL,
  PRIMARY KEY (`occurencyID`),
  KEY `keyID` (`keyID`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=3 ;

--
-- Dumping data for table `keywords-occurencies`
--

INSERT INTO `keywords-occurencies` (`occurencyID`, `keyID`, `date`) VALUES
(1, 1, '2013-01-27'),
(2, 1, '2013-01-26');

--
-- Constraints for table `keywords-occurencies`
--
ALTER TABLE `keywords-occurencies`
  ADD CONSTRAINT `keywords@002doccurencies_ibfk_1` FOREIGN KEY (`keyID`) REFERENCES `keywords` (`keyID`) ON DELETE CASCADE ON UPDATE CASCADE;

---

在日期上打勾：

SELECT 
`keywords`.keyID, 
count(`keywords-occurencies`.keyID) as countOccurencies 
FROM `keywords-occurencies`  
LEFT JOIN `keywords`  ON `keywords-occurencies`.keyID = `keywords`.keyID 
WHERE `keywords-occurencies`.`keyID` IN (1,2,3) AND `date` BETWEEN '2013/01/25' AND '2013/01/27'
GROUP BY `keywords-occurencies`.`keyID`

要做的事情

• 您应该使用

  按关键字分组。keyID

• 而且您必须显示的是

  关键字发生率.keyID

  而不是

  关键字.keyID

• 计数

  关键字.keyID

• （可选）使用

  别名

  ，这样您就可以消除表名以外的反勾号

质疑,

SELECT  a.keyID,
        count(b.keyID) AS countOccurencies
FROM    `keywords - occurencies` a
        LEFT JOIN `keywords` b
            ON a.keyID = b.keyID
WHERE   a.keyID IN ( 1, 2, 3 ) AND 
        DATE BETWEEN '2013/01/25' AND '2013/01/27'
GROUP   BY a.keyID

SELECT  a.keyID,
        count(b.keyID) AS countOccurencies
FROM    `keywords` a
        LEFT JOIN `keywords-occurencies` b
            ON a.keyID = b.keyID AND
               b.DATE BETWEEN '2013-01-25' AND '2013-01-27'
WHERE   a.keyID IN ( 1, 2, 3 ) 
GROUP   BY a.keyID

更新1

根据示例记录，您需要执行以下操作：

• 交换桌名
• 将此条件

  日期介于'2013-01-25'和'2013-01-27'之间

  放在连接条款的

  上

• （可选）使用

  别名

  ，这样您就可以消除表名以外的反勾号

质疑,

SELECT  a.keyID,
        count(b.keyID) AS countOccurencies
FROM    `keywords - occurencies` a
        LEFT JOIN `keywords` b
            ON a.keyID = b.keyID
WHERE   a.keyID IN ( 1, 2, 3 ) AND 
        DATE BETWEEN '2013/01/25' AND '2013/01/27'
GROUP   BY a.keyID

SELECT  a.keyID,
        count(b.keyID) AS countOccurencies
FROM    `keywords` a
        LEFT JOIN `keywords-occurencies` b
            ON a.keyID = b.keyID AND
               b.DATE BETWEEN '2013-01-25' AND '2013-01-27'
WHERE   a.keyID IN ( 1, 2, 3 ) 
GROUP   BY a.keyID

---

有两件事。您需要根据左侧外部联接的第一部分上的id进行分组。然后你需要数一数第二面是什么。对于右外部联接，顺序相反：

SELECT k.keyID, count(ko.keyID) as countOccurencies 
FROM `keywords-occurencies` ko
      RIGHT JOIN `keywords` k
      ON ko.keyID = k.keyID 
WHERE k.`keyID` IN (1,2,3) AND date BETWEEN '2013/01/25' AND '2013/01/27'
GROUP BY k.`keyID`

其原因与左侧外部联接有关。它将所有内容保留在第一个表中，即使没有匹配项。所以，这就是你得到完整列表的地方。至于计数，您要对匹配项进行计数。如果在第一个表中计算id，则始终会得到至少1。计算第二个表中的id可以得到0

---

请注意，我还向您的表中添加了别名，以使查询更具可读性。
将其更改为

左连接对我来说很有效：

SELECT k.keyID, count(ko.keyID) as countOccurencies 
FROM `keywords-occurencies` ko
      LEFT JOIN `keywords` k
      ON ko.keyID = k.keyID 
WHERE k.`keyID` IN (1,2,3) AND date BETWEEN '2013/01/25' AND '2013/01/27'
GROUP BY k.`keyID`

谢谢您的更正，但是上面的查询仍然没有返回0结果行。您能提供我们可以使用的示例记录吗？当然，我将它们添加到了我的问题中。我认为您需要交换这些表名，并在加入它们时将的条件放在，而不是放在
WHERE
子句上。将所有左连接的列依赖项移动到左连接子句（而不是in和子句）中，对我来说也非常有效。非常感谢。谢谢，但查询仍然不会返回0结果行。@SportBilly。根据表的名称，我认为您需要一个正确的外部联接——我猜关键字表包含所有关键字，并且出现的值可能为0。我相应地修改了查询。@SashiKant关于刚才的问题。。。真的评论没有意义；）欢迎来到StackOverflow。要在文章中插入代码，请使用“代码示例”按钮，而不是“代码片段”按钮。snippet按钮仅适用于HTML/CSS/JS