我们再来一次......
[编辑]底部有一个用SQL生成测试数据库的更新。 [编辑]
我现在已经挣扎了几天，对我来说是一个相当复杂的SQL查询。如果没有得到SO的很多帮助，我就不会得到这么多，这些帮助已经让我学到了很多SQL。
我会尝试引导您完成设置，以便您了解我正在尝试做什么。请耐心等待......
我有一个带有整数属性的表（IntegerAttributes）。 ID是项ID，其中Key是附加到ID为“ID”的Item的属性的名称，Value是属性的值，只能是整数。一个项目可以有0到多个属性。
IntegerAttributes
ID Key Value
1 Location 3
1 Color 5
2 Location 1
3 Color 3
属性“位置”的值是另一个名为“位置”
的表中的IDLocations
ID Location etc...
1 Boston
2 Manilla
3 Stockholm
4 Beijing
属性“Color”的值是另一个名为“Colors”
的表中的IDLocations
ID Color
1 Blue
2 Black
3 White
4 Red
5 Green
还有一个类似的表（StringAttributes）表，其工作方式与IntegerAttributes相同，但Value列是text。 IntegerAttributes和StringAttributes组合在一起并转换为带有UNION ALL的字符串。
此时持有每个项目的表格非常简单：
ID Checkin
1 2010-01-22 11:28:18
2 2010-01-21 16:27:54
3 2010-01-20 18:40:07
到目前为止，一切都很清楚，但现在变得复杂了：
这是我用来获取所有属性并将它们连接成JSON字符串并获取Item数据的SQL Query
SELECT
i.ID,
i.Checkin,
CONCAT('{\"Date\":\"',i.Checkin,'\",', GROUP_CONCAT('\"',Attribute.key, '\":\"', CONVERT(Attribute.value,CHAR), '\"'), '}') as Attributes
# , l.Location
FROM (
SELECT ItemID, ats.Key, ats.Value
FROM attributeStrings as ats
UNION ALL
SELECT ItemID, ati.Key, ati.Value
FROM attributeIntegers as ati
) Attribute
JOIN Items i ON i.ID = Attribute.ItemID
# JOIN locations l ON (Attribute.Key = 'Location' AND l.ID = Attribute.Value)
GROUP BY ItemID
ORDER BY i.ID DESC
正如你所看到的，我已经说了两句话，我很快就会回过头来看。
上面的查询结果如下：
ID Checkin Attributes
1 2010-01-22 11:28:18 {"Date":"2010-01-22 11:28:18","Location":"3","Color":"5"}
2 2010-01-21 16:27:54 {"Date":"2010-01-21 16:27:54","Location":"1"}
3 2010-01-20 18:40:07 {"Date":"2010-01-20 18:40:07","Color":"3"}
到目前为止一切顺利。
但是现在我想要包含“位置”的查找（最后是'Color'或其他带有lookup-ID的属性）。
如果我取消注释上面查询中的两行
# , l.Location
# JOIN locations l ON (Attribute.Key = 'Location' AND l.ID = Attribute.Value)
我只得到结果，其中唯一的属性是“位置”，而属性字段现在只包含“日期”和“位置”属性。
ID Checkin Attributes Location
2 2010-01-21 16:27:54 {"Date":"2010-01-21 16:27:54","Location":"1"} Boston
我想要的结果与之前一样，但是在“位置”中有一个额外的列（后面是更多的查找列）属性。
我想要的例子：
ID Checkin Attributes Location Color
1 2010-01-22 11:28:18 {"Date":"2010-01-22 11:28:18","Location":"3","Color":"5"} Stockholm Green
2 2010-01-21 16:27:54 {"Date":"2010-01-21 16:27:54","Location":"1"} Boston null
3 2010-01-20 18:40:07 {"Date":"2010-01-20 18:40:07","Color":"3"} null White
感谢您一直在这里阅读：D 我试图用IF EXISTS详细说明，但我无法弄清楚如何做到这一点。
[编辑] SQL生成测试数据库[编辑]
-- MySQL Administrator dump 1.4
--
-- ------------------------------------------------------
-- Server version 5.1.47-community
/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
/*!40101 SET NAMES utf8 */;
/*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;
/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
/*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;
--
-- Create schema swebussandbox
--
CREATE DATABASE IF NOT EXISTS SODatabase;
USE SODatabase;
--
-- Definition of table `attributeintegers`
--
DROP TABLE IF EXISTS `attributeintegers`;
CREATE TABLE `attributeintegers` (
`ItemID` int(10) unsigned NOT NULL,
`Key` varchar(45) NOT NULL,
`Value` int(10) unsigned DEFAULT NULL,
PRIMARY KEY (`ItemID`,`Key`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 ROW_FORMAT=DYNAMIC;
--
-- Dumping data for table `attributeintegers`
--
/*!40000 ALTER TABLE `attributeintegers` DISABLE KEYS */;
INSERT INTO `attributeintegers` (`ItemID`,`Key`,`Value`) VALUES
(4,'Color',17),
(4,'Location',3),
(5,'Location',2),
(6,'Location',6),
(7,'Color',15),
(8,'Location',8),
(9,'Location',10),
(10,'Color',15),
(10,'Location',2),
(11,'Color',15),
(11,'Location',4),
(12,'Color',15),
(12,'Location',3),
(13,'Color',15),
(13,'Location',8),
(14,'Location',3),
(15,'Location',6),
(16,'Color',18),
(18,'Color',15),
(18,'Location',4);
/*!40000 ALTER TABLE `attributeintegers` ENABLE KEYS */;
--
-- Definition of table `attributestrings`
--
DROP TABLE IF EXISTS `attributestrings`;
CREATE TABLE `attributestrings` (
`ItemID` int(10) unsigned NOT NULL DEFAULT '0',
`Key` varchar(45) NOT NULL DEFAULT '_NA_',
`Value` text,
PRIMARY KEY (`ItemID`,`Key`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 ROW_FORMAT=DYNAMIC;
--
-- Dumping data for table `attributestrings`
--
/*!40000 ALTER TABLE `attributestrings` DISABLE KEYS */;
INSERT INTO `attributestrings` (`ItemID`,`Key`,`Value`) VALUES
(5,'Type','BagForm'),
(6,'Type','BagForm'),
(9,'Type','BagForm'),
(10,'Type','BagForm'),
(11,'Type','BagForm'),
(12,'Brand','Bogcase'),
(12,'Type','BagForm'),
(14,'Type','BagForm'),
(15,'Brand','Carryline World Wide'),
(15,'Type','BagForm'),
(16,'Brand','Fjällräven'),
(16,'Type','BagForm'),
(17,'Brand','Packard Bell'),
(17,'Tech','ComputerForm'),
(17,'Type','TechGUI');
/*!40000 ALTER TABLE `attributestrings` ENABLE KEYS */;
--
-- Definition of table `colors`
--
DROP TABLE IF EXISTS `colors`;
CREATE TABLE `colors` (
`ID` int(10) unsigned NOT NULL AUTO_INCREMENT,
`Color` varchar(45) NOT NULL,
PRIMARY KEY (`ID`)
) ENGINE=InnoDB AUTO_INCREMENT=16 DEFAULT CHARSET=utf8;
--
-- Dumping data for table `colors`
--
/*!40000 ALTER TABLE `colors` DISABLE KEYS */;
INSERT INTO `colors` (`ID`,`Color`) VALUES
(1,'Multicolored'),
(2,'Black'),
(3,'White'),
(4,'Red'),
(5,'Green'),
(6,'Blue'),
(7,'Yellow'),
(8,'Black'),
(9,'Gold'),
(10,'Bown'),
(11,'Purpul'),
(12,'Pink'),
(13,'Orange'),
(14,'Gray'),
(15,'Transparent');
/*!40000 ALTER TABLE `colors` ENABLE KEYS */;
--
-- Definition of table `items`
--
DROP TABLE IF EXISTS `items`;
CREATE TABLE `items` (
`ID` int(10) unsigned NOT NULL AUTO_INCREMENT,
`CheckIn` datetime DEFAULT NULL,
`Line` int(10) unsigned DEFAULT NULL,
`TypeID` int(10) unsigned DEFAULT NULL,
`SizeID` int(10) unsigned DEFAULT NULL,
`ColorID` int(10) unsigned DEFAULT NULL,
`MaterialID` int(10) unsigned DEFAULT NULL,
`CheckOut` datetime DEFAULT NULL,
`LocationID` int(10) unsigned DEFAULT NULL,
`Notes` text,
`Tur` int(10) unsigned DEFAULT NULL,
`Bus` int(10) unsigned DEFAULT NULL,
PRIMARY KEY (`ID`),
FULLTEXT KEY `NoteIndex` (`Notes`)
) ENGINE=MyISAM AUTO_INCREMENT=12 DEFAULT CHARSET=utf8 PACK_KEYS=1;
--
-- Dumping data for table `items`
--
/*!40000 ALTER TABLE `items` DISABLE KEYS */;
INSERT INTO `items` (`ID`,`CheckIn`) VALUES
(4,'2010-12-03 02:04:38'),
(5,'2010-12-27 02:11:25'),
(6,'2010-12-27 02:14:28'),
(7,'2010-12-25 02:17:09'),
(8,'2010-12-24 02:33:49'),
(9,'2011-01-06 07:48:16'),
(10,'2011-01-06 07:47:09'),
(11,'2010-12-31 10:53:26');
/*!40000 ALTER TABLE `items` ENABLE KEYS */;
--
-- Definition of table `locations`
--
DROP TABLE IF EXISTS `locations`;
CREATE TABLE `locations` (
`ID` int(10) unsigned NOT NULL AUTO_INCREMENT,
`Location` varchar(45) NOT NULL,
`Group` int(10) unsigned NOT NULL DEFAULT '1',
`Address` text,
`Phone` varchar(20) DEFAULT NULL,
`Contact` varchar(45) DEFAULT NULL,
`Hours` varchar(45) DEFAULT NULL,
PRIMARY KEY (`ID`)
) ENGINE=InnoDB AUTO_INCREMENT=14 DEFAULT CHARSET=utf8;
--
-- Dumping data for table `locations`
--
/*!40000 ALTER TABLE `locations` DISABLE KEYS */;
INSERT INTO `locations` (`ID`,`Location`) VALUES
(1,'Boston'),
(2,'Stockholm'),
(3,'Manilla'),
(4,'Berlin'),
(5,'Oslo'),
(6,'Paris'),
(7,'London'),
(8,'Amsterdam'),
(9,'Helsinki'),
(10,'Kopenhagen'),
(11,'Barselona'),
(12,'Luxenbourg'),
(13,'Milano');
/*!40000 ALTER TABLE `locations` ENABLE KEYS */;
/*!40101 SET SQL_MODE=@OLD_SQL_MODE */;
/*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */;
/*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */;
/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;
/*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */;
/*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;
/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;
我使用此更新的查询尝试了 Tumbler 的建议：
SELECT
i.ID,
i.Checkin,
CONCAT('{\"Date\":\"',i.Checkin,'\",', GROUP_CONCAT('\"',Attribute.key, '\":\"', CONVERT(Attribute.value,CHAR), '\"'), '}') as Attributes,
COALESCE(l.Location,null) as Location,
COALESCE(c.Color,null) as Color
FROM (
SELECT ItemID, ats.Key, ats.Value
FROM attributeStrings as ats
UNION ALL
SELECT ItemID, ati.Key, ati.Value
FROM attributeIntegers as ati
) Attribute
LEFT JOIN locations l ON (Attribute.Key = 'Location' AND l.ID = Attribute.Value)
LEFT JOIN Colors c ON (Attribute.Key = 'Color' AND c.ID = Attribute.Value)
JOIN Items i ON i.ID = Attribute.ItemID
GROUP BY ItemID
ORDER BY i.ID DESC
...但它确实显示了所有属性，但仅适用于将Location或color作为ONLY属性的项目。
答案 0 :(得分：2)
尝试左连接
LEFT JOIN locations l ON (Attribute.Key = 'Location' AND l.ID = Attribute.Value)
如果空值出现问题：
, COALESCE(l.Location,'No Location')
你的例子有点太复杂，不容易复制，但让我们知道它是怎么回事。
答案 1 :(得分：1)
SELECT i.ID, i.checkin,
CONCAT('{\"Date\":\"', i.checkin,'\",', GROUP_CONCAT('\"', attribute.key, '\":\"', CONVERT(attribute.value,CHAR), '\"'), '}') as attributes,
l.location, c.color
FROM (
SELECT ItemID, ats.key, ats.value
FROM attributestrings as ats
UNION ALL
SELECT ItemID, ati.Key, ati.Value
FROM attributeintegers as ati
) attribute
JOIN items i
ON i.ID = attribute.itemid
LEFT JOIN
attributeintegers atli
ON atli.itemid = i.id
AND atli.key = 'Location'
LEFT JOIN
locations l
ON l.id = atli.value
LEFT JOIN
attributeintegers atci
ON atci.itemid = i.id
AND atci.key = 'Color'
LEFT JOIN
colors c
ON c.id = atci.value
GROUP BY
i.id DESC