mysql - 错误111，组函数使用无效

Question

SELECT DISTINCT CONCAT('TOTAL NUMBER OF LEGS IN A TRIP NUMBER ', T1.TNUM, ' IS NOT EQUAL TO THE LARGEST NUMBER OF LEG IN THE TRIP') AS 'ERR'
FROM TRIPLEG T1
WHERE MAX(T1.LEGNUM) = (SELECT COUNT(T2.TNUM) 
                    FROM TRIPLEG
                    WHERE T1.TNUM = T2.TNUM);

通过我的代码，我试图找到所有违反以下一致性约束的行程。每次行程的最后一段航程必须等于一次行程的总航段数"

CREATE TABLE TRIPLEG(
TNUM    DECIMAL(10)     NOT NULL,
LEGNUM  DECIMAL(2)  NOT NULL,
DEPARTURE VARCHAR(30)   NOT NULL,     DESTINATION VARCHAR(30) NOT NULL,
    CONSTRAINT TRIPLEG_PKEY PRIMARY KEY (TNUM, LEGNUM),
    CONSTRAINT TRIPLEG_UNIQUE UNIQUE(TNUM, DEPARTURE, DESTINATION),
CONSTRAINT TRIPLEG_FKEY1 FOREIGN KEY (TNUM) REFERENCES TRIP(TNUM) );

INSERT INTO TRIPLEG VALUES( 1, 1, 'Sydney', 'Melbourne');
INSERT INTO TRIPLEG VALUES( 1, 2, 'Melbourne', 'Hobart');

Answer 1

尝试以下操作；)

SELECT DISTINCT CONCAT('TOTAL NUMBER OF LEGS IN A TRIP NUMBER ', T1.TNUM, ' IS NOT EQUAL TO THE LARGEST NUMBER OF LEG IN THE TRIP') AS 'ERR'
FROM TRIPLEG T1
GROUP BY T1.TNUM
HAVING COUNT(T1.TNUM) <> MAX(T1.LEGNUM)