SQl count（）帮助select语句

Question

我正在使用此代码：

  SELECT MACH_NO, 
         COUNT(MACH_NO) AS TOTAL_REPORTS
    FROM MAINTENANCE_LOG
GROUP BY MACH_NO;

...检索一些数据：

MACH_NO  TOTAL_REPORTS
----------------------
1        4
5        2
8        1
7        1

如何仅检索总报告大于3的位置？我试过了：

WHERE TOTAL_REPORTS > 3 

......但它说

  

ORA-00904：“TOTAL_REPORTS”：标识符无效

Answer 1

由于您使用的是GROUP BY，因此您应该使用HAVING而不是WHERE。您还需要明确使用COUNT(MACH_NO)而不是TOTAL_REPORTS的别名。

因此请使用HAVING COUNT(MACH_NO) > 3，而不是WHERE TOTAL_REPORTS > 3。

SELECT MACH_NO, 
       COUNT(MACH_NO) AS TOTAL_REPORTS 
FROM MAINTENANCE_LOG 
GROUP BY MACH_NO
HAVING COUNT(MACH_NO) > 3;

Answer 2

使用HAVING条款

SELECT MACH_NO, COUNT(MACH_NO) AS TOTAL_REPORTS FROM MAINTENANCE_LOG GROUP BY MACH_NO HAVING TOTAL_REPORTS > 3;

Answer 3

通过MACH_NO从MAINTENANCE_LOG GROUP中选择MACH_NO，COUNT（MACH_NO）AS TOTAL_REPORTS having count(mach_no) > 3

Answer 4

而不是WHERE TOTAL_REPORTS＆gt; 3，尝试WHERE COUNT（MACH_NO）＆gt; 3。