SQL SELECT字符串大于使用count（）

Question

我想列出的毕业生比本科生更多。 我觉得我的想法背后有这个概念，但是进行查询比简单翻译要困难一些。 下面是我的代码，我目前正在得到一个错误的右括号错误，其中COUNT（student.career ='GRD'）。 谢谢。

SELECT studentgroup.name 
COUNT(student.career = 'GRD') - COUNT(student.career = 'UGRD') 
AS Gradnum FROM studentgroup 
INNER JOIN memberof ON studentgroup.GID = memberof.GroupID
INNER JOIN student ON memberof.StudentID = student.SID
WHERE Gradnum > 1;

Answer 1

SELECT studentgroup.name 
SUM(CASE WHEN student.career = 'GRD' THEN 1 ELSE 0 END) - SUM(CASE WHEN student.career = 'UGRD' THEN 1 ELSE 0 END) 
AS Gradnum FROM studentgroup 
INNER JOIN memberof ON studentgroup.GID = memberof.GroupID
INNER JOIN student ON memberof.StudentID = student.SID
WHERE Gradnum > 1
GROUP BY studentgroup.name;

Answer 2

SELECT studentgroup.GID, max(studentgroup.name)
FROM studentgroup 
INNER JOIN memberof ON studentgroup.GID = memberof.GroupID
INNER JOIN student ON memberof.StudentID = student.SID
GROUP BY studentgroup.GID
HAVING SUM(CASE WHEN student.career = 'GRD' THEN 1 
                WHEN student.career = 'UGRD'THEN -1
                ELSE 0
            END) >0

Answer 3

我使用了WITH As子句，它支持大多数DBMS，如SQL Server，PostGresSQL，除了MySQL

With grpTbl As
(

SELECT studentgroup.name As StudentGroupName,
       SUM( CASE WHEN student.career = 'GRD' THEN 1 ELSE 0 END ) AS 'TotalGraduate',
       SUM( CASE WHEN student.career = 'UGRD' THEN 1 ELSE 0 END ) AS 'TotalUnderGraduate'

FROM studentgroup 
INNER JOIN memberof ON studentgroup.GID = memberof.GroupID
INNER JOIN student ON memberof.StudentID = student.SID

)


SELECT StudentGroupName
FROM grpTbl 
WHERE TotalGraduate > TotalUnderGraduate

对于MySQL，您可以使用临时表来存储来自First查询的结果集，并过滤出在WHERE子句中具有更多研究生而不是UnderGraduate的GroupNames。 这种方法对其他DBMS也有效，也就是创建临时表的语法不同。

CREATE TEMPORARY TABLE grpTbl (
StudentGroupName varchar(255),
TotalGraduate INT,
TotalUnderGraduate INT
);


INSERT INTO grpTbl
SELECT studentgroup.name As StudentGroupName,
           SUM( CASE WHEN student.career = 'GRD' THEN 1 ELSE 0 END ) ,
           SUM( CASE WHEN student.career = 'UGRD' THEN 1 ELSE 0 END ) 

    FROM studentgroup 
    INNER JOIN memberof ON studentgroup.GID = memberof.GroupID
    INNER JOIN student ON memberof.StudentID = student.SID 


 SELECT StudentGroupName
    FROM grpTbl 
    WHERE TotalGraduate > TotalUnderGraduate


 DROP TABLE grpTbl 

Answer 4

还有一个选择

SELECT studentgroup.name
FROM studentgroup INNER JOIN memberof ON studentgroup.GID = memberof.GroupID
                  INNER JOIN student ON memberof.StudentID = student.SID
GROUP BY studentgroup.name
HAVING COUNT(CASE WHEN student.career = 'GRD' THEN student.career END) 
         > COUNT(CASE WHEN student.career = 'UGRD' THEN student.career END)