左连接不会返回mysql中左表中的所有行

我真的不明白为什么left join不返回t1中的所有行。请帮忙，我们将不胜感激

t1模式：

 CREATE TABLE `tbl_assigned` (
     `ID` int(11) NOT NULL AUTO_INCREMENT,
     `Round` int(2) NOT NULL,
     `TraineeID` varchar(7) NOT NULL,
     `Name` varchar(25) NOT NULL,
     `Mobile` int(10) DEFAULT NULL,
     `BatchID` varchar(35) NOT NULL,
     `Remarks` varchar(8) DEFAULT NULL,
     `District` varchar(15) DEFAULT NULL,
     `Comments` varchar(21) DEFAULT NULL,
     `Level` varchar(2) DEFAULT NULL,
     `Trade` int(1) DEFAULT NULL,
     `Status` int(1) DEFAULT NULL,
     `Photo` varchar(50) DEFAULT NULL,
     PRIMARY KEY (`ID`),
     KEY `TraineeID` (`TraineeID`)
    ) ENGINE=InnoDB AUTO_INCREMENT=356 DEFAULT CHARSET=utf8

CREATE TABLE `tbl_attn_temp` (
 `ID` int(11) NOT NULL AUTO_INCREMENT,
 `TraineeID` varchar(7) NOT NULL,
 `ScannerID` int(7) NOT NULL,
 `attnDate` date NOT NULL,
 `attnTime` time NOT NULL,
 `Status` tinyint(1) NOT NULL DEFAULT '1',
 PRIMARY KEY (`ID`)
) ENGINE=InnoDB AUTO_INCREMENT=2135 DEFAULT CHARSET=latin1

SELECT t1.TraineeID, t2.attnDate
FROM tbl_assigned t1
LEFT JOIN tbl_attn_temp t2 on t1.TraineeID=t2.TraineeID
WHERE t1.BatchID='ID-Welding/SSTS-01M/R7/01' and t2.attnDate='2015-12-28'

TID   attnDate
15950 2015-12-28
24310 2015-12-28
24317 2015-12-28
24327 2015-12-28
24400 2015-12-28
24973 2015-12-28
25186 2015-12-28
25281 2015-12-28
25285 2015-12-28
25300 2015-12-28

t2模式：

 CREATE TABLE `tbl_assigned` (
     `ID` int(11) NOT NULL AUTO_INCREMENT,
     `Round` int(2) NOT NULL,
     `TraineeID` varchar(7) NOT NULL,
     `Name` varchar(25) NOT NULL,
     `Mobile` int(10) DEFAULT NULL,
     `BatchID` varchar(35) NOT NULL,
     `Remarks` varchar(8) DEFAULT NULL,
     `District` varchar(15) DEFAULT NULL,
     `Comments` varchar(21) DEFAULT NULL,
     `Level` varchar(2) DEFAULT NULL,
     `Trade` int(1) DEFAULT NULL,
     `Status` int(1) DEFAULT NULL,
     `Photo` varchar(50) DEFAULT NULL,
     PRIMARY KEY (`ID`),
     KEY `TraineeID` (`TraineeID`)
    ) ENGINE=InnoDB AUTO_INCREMENT=356 DEFAULT CHARSET=utf8

CREATE TABLE `tbl_attn_temp` (
 `ID` int(11) NOT NULL AUTO_INCREMENT,
 `TraineeID` varchar(7) NOT NULL,
 `ScannerID` int(7) NOT NULL,
 `attnDate` date NOT NULL,
 `attnTime` time NOT NULL,
 `Status` tinyint(1) NOT NULL DEFAULT '1',
 PRIMARY KEY (`ID`)
) ENGINE=InnoDB AUTO_INCREMENT=2135 DEFAULT CHARSET=latin1

SELECT t1.TraineeID, t2.attnDate
FROM tbl_assigned t1
LEFT JOIN tbl_attn_temp t2 on t1.TraineeID=t2.TraineeID
WHERE t1.BatchID='ID-Welding/SSTS-01M/R7/01' and t2.attnDate='2015-12-28'

TID   attnDate
15950 2015-12-28
24310 2015-12-28
24317 2015-12-28
24327 2015-12-28
24400 2015-12-28
24973 2015-12-28
25186 2015-12-28
25281 2015-12-28
25285 2015-12-28
25300 2015-12-28

查询：

 CREATE TABLE `tbl_assigned` (
     `ID` int(11) NOT NULL AUTO_INCREMENT,
     `Round` int(2) NOT NULL,
     `TraineeID` varchar(7) NOT NULL,
     `Name` varchar(25) NOT NULL,
     `Mobile` int(10) DEFAULT NULL,
     `BatchID` varchar(35) NOT NULL,
     `Remarks` varchar(8) DEFAULT NULL,
     `District` varchar(15) DEFAULT NULL,
     `Comments` varchar(21) DEFAULT NULL,
     `Level` varchar(2) DEFAULT NULL,
     `Trade` int(1) DEFAULT NULL,
     `Status` int(1) DEFAULT NULL,
     `Photo` varchar(50) DEFAULT NULL,
     PRIMARY KEY (`ID`),
     KEY `TraineeID` (`TraineeID`)
    ) ENGINE=InnoDB AUTO_INCREMENT=356 DEFAULT CHARSET=utf8

CREATE TABLE `tbl_attn_temp` (
 `ID` int(11) NOT NULL AUTO_INCREMENT,
 `TraineeID` varchar(7) NOT NULL,
 `ScannerID` int(7) NOT NULL,
 `attnDate` date NOT NULL,
 `attnTime` time NOT NULL,
 `Status` tinyint(1) NOT NULL DEFAULT '1',
 PRIMARY KEY (`ID`)
) ENGINE=InnoDB AUTO_INCREMENT=2135 DEFAULT CHARSET=latin1

SELECT t1.TraineeID, t2.attnDate
FROM tbl_assigned t1
LEFT JOIN tbl_attn_temp t2 on t1.TraineeID=t2.TraineeID
WHERE t1.BatchID='ID-Welding/SSTS-01M/R7/01' and t2.attnDate='2015-12-28'

TID   attnDate
15950 2015-12-28
24310 2015-12-28
24317 2015-12-28
24327 2015-12-28
24400 2015-12-28
24973 2015-12-28
25186 2015-12-28
25281 2015-12-28
25285 2015-12-28
25300 2015-12-28

输出：

 CREATE TABLE `tbl_assigned` (
     `ID` int(11) NOT NULL AUTO_INCREMENT,
     `Round` int(2) NOT NULL,
     `TraineeID` varchar(7) NOT NULL,
     `Name` varchar(25) NOT NULL,
     `Mobile` int(10) DEFAULT NULL,
     `BatchID` varchar(35) NOT NULL,
     `Remarks` varchar(8) DEFAULT NULL,
     `District` varchar(15) DEFAULT NULL,
     `Comments` varchar(21) DEFAULT NULL,
     `Level` varchar(2) DEFAULT NULL,
     `Trade` int(1) DEFAULT NULL,
     `Status` int(1) DEFAULT NULL,
     `Photo` varchar(50) DEFAULT NULL,
     PRIMARY KEY (`ID`),
     KEY `TraineeID` (`TraineeID`)
    ) ENGINE=InnoDB AUTO_INCREMENT=356 DEFAULT CHARSET=utf8

CREATE TABLE `tbl_attn_temp` (
 `ID` int(11) NOT NULL AUTO_INCREMENT,
 `TraineeID` varchar(7) NOT NULL,
 `ScannerID` int(7) NOT NULL,
 `attnDate` date NOT NULL,
 `attnTime` time NOT NULL,
 `Status` tinyint(1) NOT NULL DEFAULT '1',
 PRIMARY KEY (`ID`)
) ENGINE=InnoDB AUTO_INCREMENT=2135 DEFAULT CHARSET=latin1

SELECT t1.TraineeID, t2.attnDate
FROM tbl_assigned t1
LEFT JOIN tbl_attn_temp t2 on t1.TraineeID=t2.TraineeID
WHERE t1.BatchID='ID-Welding/SSTS-01M/R7/01' and t2.attnDate='2015-12-28'

TID   attnDate
15950 2015-12-28
24310 2015-12-28
24317 2015-12-28
24327 2015-12-28
24400 2015-12-28
24973 2015-12-28
25186 2015-12-28
25281 2015-12-28
25285 2015-12-28
25300 2015-12-28

但t1表中有15个符合此标准的受训人员

SELECT t1.TraineeID FROM tbl_assigned t1 WHERE t1.BatchID='ID-Welding/SSTS-01M/R7/01'

输出：

15950
20012
21173
24310
24317
24327
24400
24936
24973
25033
25186
25281
25282
25285
25300

SELECT t2.TraineeID, t2.attnDate FROM tbl_attn_temp t2 WHERE t2.attnDate='2015-12-28'

输出：

ID        Date
SSTS001 2015-12-28
SSTS001 2015-12-28
SSTS001 2015-12-28
15950 2015-12-28
24317 2015-12-28
24738 2015-12-28
25186 2015-12-28
25281 2015-12-28
24973 2015-12-28
24310 2015-12-28
24400 2015-12-28
24327 2015-12-28
25300 2015-12-28
25285 2015-12-28
SSTS002 2015-12-28
28702 2015-12-28
28702 2015-12-28
22934 2015-12-28
26620 2015-12-28
24068 2015-12-28
21343 2015-12-28
1151467 2015-12-28
24931 2015-12-28
24931 2015-12-28
24931 2015-12-28
4872 2015-12-28
24071 2015-12-28
24786 2015-12-28
6203 2015-12-28
24069 2015-12-28

---

检查BatchID字段中是否存在空间问题。空格可能位于缺失记录的开头和结尾

还要检查其他记录的日期

处理记录开始和结束时可能出现的空间问题

使用此查询

SELECT t1.TraineeID, t2.attnDate
FROM tbl_assigned t1
LEFT JOIN tbl_attn_temp t2 on t1.TraineeID=t2.TraineeID
WHERE ifnull(trim(t1.BatchID),'')='ID-Welding/SSTS-01M/R7/01'

---

如果您获得了预期记录，则检查其他记录中的日期是否为“2015-12-28”。

您的预期结果是什么？您的预期行是否被

WHERE

子句过滤掉，以查找

t2。attnDate='2015-12-28'

？WHERE子句将过滤结果

t1.BatchID='ID-Welding/SSTS-01M/R7/01'

删除条件

t1.BatchID='ID-Welding/SSTS-01M/R7/01'

然后您可以获得预期的output@ChrisNauroth-是的，先生，

t2.attnDate='2015-12-28'

过滤掉了预期结果。先生，这里没有空间问题，因为许多其他查询都使用参数运行，工作正常。谢谢合作。好的，如果你运行上面的查询，它会给你包含你想要的结果的列表吗？BatchID字段的数据有问题。如果没有所需的表数据可用，则无法进行任何解析。