SQLite查询选择另一个表中不存在的所有记录

Question

I am having some problem when trying to perform a SQLite query to get the records which does not exist from another table. Basically I have two database tables:

My exercise table stored all the exercises available whereas the bookedExercise table store the exercises booked by each users. What I am trying to do is, for example if the exercise does exist in the bookedExercise, it should be filtered out.

Here is the SQLite query which I used:

SELECT exercise.exerciseID, exercise.exerciseType, exercise.amout FROM exercise LEFT JOIN bookedExercise WHERE exercise.exerciseID = bookedExercise.exerciseID AND bookedExercise.exerciseID IS NULL

However, it returned me empty records. Any ideas?

Thanks in advance.

Answer 1

如果您不使用联接很好，则可以使用

SELECT * FROM exercise WHERE exerciseID not in (SELECT exerciseID FROM bookedExercise)

Answer 2

Your SQL looked okay... I think the problem might be you have a datatype mismatch. You have exercise ID as an integer in one table and text in another.

Also, if you have huge data volumes, you may want to consider an anti-join:

select
  e.*
from
  exercise e
where not exists (
  select 1
  from bookedExercise be
  where
    e.excerciseId  = be.exerciseID
)

-- edit --

On second glance, your SQL was not okay. You had your join condition in the where clause. This little change would fix your existing SQL:

SELECT exercise.excerciseId , exercise.exerciseType , exercise.amout
FROM exercise LEFT JOIN bookedExercise on
    exercise.excerciseId  = bookedExercise.exerciseID
WHERE bookedExercise.exerciseID IS NULL

Answer 3

When you are using LEFT JOIN, you must put the join condition into the ON clause:

SELECT exercise.exerciseID,
       exercise.exerciseType,
       exercise.amout
FROM exercise         /* !! */
LEFT JOIN bookedExercise ON exercise.exerciseID = bookedExercise.exerciseID
WHERE bookedExercise.exerciseID IS NULL