Question

我遇到了select语句的问题。当我使用distinct时它仍会给我某些行的副本。我尝试使用group by it修复了复制但删除了其中一个值。

这是我想要输出的内容： Solution

这是我的代码：

SELECT DISTINCT M.Major, 
       S.Ethnicity = 'American Indian or Alaska Native' AS AIAN,
       S.Ethnicity = 'Asian' AS Asian,
       S.Ethnicity = 'Black or African American' AS Black,
       S.Ethnicity = 'Hispanic/Latino' AS Hisp,
       S.Ethnicity = 'Native Hawaiian or Other Pacific Islander' AS Native,
       S.Ethnicity = 'White' AS White,
       S.Ethnicity = 'Unknown/Other' As Other
FROM STUDENT AS S, MAJOR AS M
WHERE S.Major_ID = M.MajorID and S.Gender = 'Female'
Group By M.Major;

STUDENT | 
   CREATE TABLE `STUDENT` (
  `StudentID` int(11) NOT NULL AUTO_INCREMENT,
  `FirstName` char(35) NOT NULL,
  `LastName` char(35) NOT NULL,
  `DateOfBirth` date NOT NULL,
  `SSN` char(11) NOT NULL,
  `GGCEmail` varchar(100) NOT NULL,
  `Gender` char(6) NOT NULL,
  `Ethnicity` char(100) NOT NULL,
  `IsGrad` char(3) NOT NULL,
  `Major_ID` int(11) NOT NULL,
  `Minor_ID` int(11) DEFAULT NULL,
  `Timestamp` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE   CURRENT_TIMESTAMP,
  PRIMARY KEY (`StudentID`),
  KEY `MAJOR_STUDENT_FK` (`Major_ID`),
  KEY `MINOR_STUDENT_FK` (`Minor_ID`),
  CONSTRAINT `MAJOR_STUDENT_FK` FOREIGN KEY (`Major_ID`) REFERENCES `MAJOR` (`MajorID`),
  CONSTRAINT `MINOR_STUDENT_FK` FOREIGN KEY (`Minor_ID`) REFERENCES `MINOR` (`MinorID`)

MAJOR | 
CREATE TABLE `MAJOR` (
  `MajorID` int(11) NOT NULL AUTO_INCREMENT,
  `Major` char(100) NOT NULL,
  `EntryGPA` decimal(3,2) NOT NULL,
  PRIMARY KEY (`MajorID`)

Answer 1

我认为你应该使用一个总和并选择案例

    SELECT DISTINCT M.Major, 
        sum( case S.Ethnicity when 'American Indian or Alaska Native' then 1 else 0 END)  AS AIAN,
        sum( case S.Ethnicity when 'Asian' then 1 else 0 END ) AS Asian,
        sum( case S.Ethnicity when 'Black or African American' then 1 else 0 END ) AS Black,
        sum( case S.Ethnicity when 'Hispanic/Latino' then 1 else 0 END) AS Hisp,
        sum( case S.Ethnicity when 'Native Hawaiian or Other Pacific Islander' then 1 else 0 END) AS Native,
        sum( case S.Ethnicity when 'White' then 1 else 0 END) AS White,
        sum( case S.Ethnicity when 'Unknown/Other' then 1 else 0 END) As Other
    FROM STUDENT AS S, MAJOR AS M
    WHERE S.Major_ID = M.MajorID and S.Gender = 'Female'
    Group By M.Major;

mysql / php合并/组合行值

1 个答案: