Question

让我们做对了。

这会返回正确的结果：

SELECT sum(w.weight * w.repetitions)
FROM workout_exercise_logs w
JOIN workout_logs wo ON `w`.`workoutLogID`=`wo`.`workoutLogID`
JOIN workouts wor ON `wo`.`workoutID`=`wor`.`workoutID`
WHERE w.weightType=1 and `wor`.`userID`=34

但是当我添加+ w.weight * w.seconds / 3时，我得到NULL结果：

SELECT sum(w.weight * w.repetitions + w.weight * w.seconds / 3)
FROM workout_exercise_logs w
JOIN workout_logs wo ON `w`.`workoutLogID`=`wo`.`workoutLogID`
JOIN workouts wor ON `wo`.`workoutID`=`wor`.`workoutID`
WHERE w.weightType=1 and `wor`.`userID`=34

表达式有什么问题，我该如何解决？谢谢！

Answer 1

一个问题，你是否真的需要这个字段可以为空（或任何字段）：秒？

如果这是一项要求，则需要将那些可以为空的字段合并为零：

SELECT sum(
      w.weight * w.repetitions 
      + w.weight * coalesce(w.seconds,0) / 3)
FROM workout_exercise_logs w
JOIN workout_logs wo ON `w`.`workoutLogID`=`wo`.`workoutLogID`
JOIN workouts wor ON `wo`.`workoutID`=`wor`.`workoutID`
WHERE w.weightType=1 and `wor`.`userID`=34

MySQL用每行的代数表达式求和

1 个答案: