mysql ORA-00979: 不是 GROUP BY 表达式

Question

-- 学生表
CREATE TABLE XS (
XSDM NUMBER(10) PRIMARY KEY,
XSMC VARCHAR(30)
);
-- 成绩表
CREATE TABLE CJ (
XSDM NUMBER(10), --学生代码
XKDM NUMBER(10), --学科代码
CJ NUMBER(3)--成绩
);

语句：
SELECT
CJ.XSDM,
XS.XSMC,
sum(CJ.CJ)
FROM
XS
LEFT JOIN CJ ON XS.XSDM = CJ.XSDM
GROUP BY CJ.XSDM;
报错：[42000][979] ORA-00979: 不是 GROUP BY 表达式

Answer 1

group by 后面还需要 XS.XSMC