我正在尝试列出毕业生比本科生更多的团体。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')。感谢。
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;
答案 0 :(得分: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;
答案 1 :(得分:1)
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
答案 2 :(得分:0)
我使用了大多数DBMS支持的WITH As子句,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。
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
答案 3 :(得分:0)
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)