Mysql和"count“

Question

我正在执行SELECT语句，我有一个问题。当你这样做的时候，例如：

select max(BMI), STDDEV(WEIGHT) FROM MEASUREMENTS where 
      MEASUREMENTS.patient_id='nick' AND 
      MEASUREMENTS.measure_date BETWEEN DATE_SUB("2013-12-30", INTERVAL 6 YEAR) AND "2013-12-30";

0的行数也算在内吗？如果是这样，我如何排除它们？因为，在我的例子中，0表示“那天没有进行测量”，所以我不想将这一天包括在我的总结果数中。

Answer 1

尝试以下操作:排除值为零的行。

您的原始声明

select max(BMI), STDDEV(WEIGHT) FROM MEASUREMENTS where MEASUREMENTS.patient_id='nick' AND MEASUREMENTS.measure_date BETWEEN DATE_SUB("2013-12-30", INTERVAL 6 YEAR) AND "2013-12-30";

您的新语句

select max(BMI), STDDEV(WEIGHT) FROM MEASUREMENTS where MEASUREMENTS.patient_id='nick' AND MEASUREMENTS.measure_date BETWEEN DATE_SUB("2013-12-30", INTERVAL 6 YEAR) AND "2013-12-30" AND MEASUREMENTS.WEIGHT <> 0;

只需添加AND MEASUREMENTS.WEIGHT <> 0即可。您也可以使用大于0的值。