单组组功能错误

Question

I'm new to SQL and am currently having an error as stated in the title for my sql.

This is my SQL query:

SELECT APPLICANT.APPNUM,APPLICANT.APPNAME,COUNT(APPLICATION.APPCNAPPNUM) AS "Total No. of Positions Applied"
FROM APPLICANT,APPLICATION
WHERE APPLICANT.APPNUM = APPLICATION.APPCNAPPNUM;

This is the Create statements:

CREATE TABLE    APPLICANT (
appNum      varchar2(10)    not null,
appName     varchar2(70),
appDOB      date,
appCity     varchar2(70),
appStreet       varchar2(70),
appHouseNum varchar2(10),
constraint applicant_Pkey primary key (appNum)
);

CREATE TABLE    APPLICATION (
appcnPosNum     varchar2(10)    not null,
appcnPosStOffrDt    date        not null,
appcnAppNum     varchar2(10)    not null,
appcnDt         date,
constraint application_Pkey primary key (appcnPosNum, appcnPosStOffrDt, appcnAppNum),
constraint application_Fkey1 foreign key (appcnPosNum, appcnPosStOffrDt) references
POSITION(posNum, posStartOfferDt),
constraint application_Fkey2 foreign key (appcnAppNum) references APPLICANT(appNum)
);

Can someone give me any suggestions as how to solve this error?

Answer 1

Use GROUP BY like:

SELECT APPLICANT.APPNUM,APPLICANT.APPNAME,COUNT(APPLICATION.APPCNAPPNUM) AS "Total No. of Positions Applied"
FROM APPLICANT,APPLICATION
WHERE APPLICANT.APPNUM = APPLICATION.APPCNAPPNUM
GROUP BY APPLICANT.APPNUM,APPLICANT.APPNAME

It's good to use also INNER JOIN instead of old school multiple tables, like:

SELECT APPLICANT.APPNUM,APPLICANT.APPNAME,COUNT(APPLICATION.APPCNAPPNUM) AS "Total No. of Positions Applied"
FROM APPLICANT
INNER JOIN APPLICATION
ON APPLICANT.APPNUM = APPLICATION.APPCNAPPNUM
GROUP BY APPLICANT.APPNUM,APPLICANT.APPNAME

Answer 2

Whenever you have an aggregate function (like COUNT) you need to include a GROUP BY clause in your query that contains all the non-aggregate fields from the "SELECT" projection. For this specific case, you need to do the following:

SELECT APPLICANT.APPNUM,APPLICANT.APPNAME,COUNT(APPLICATION.APPCNAPPNUM) AS "Total No. of     Positions Applied"
FROM APPLICANT,APPLICATION
WHERE APPLICANT.APPNUM = APPLICATION.APPCNAPPNUM
GROUP BY APPLICANT.APPNUM, APPLICANT.APPNAME;