根据表中没有其他任何条目的列值来区分表

Question

I got 2 tables where I keep location information and people's locations. I want to find rows that people who are inside without leaving the place. So I have client id and location id in the both tables. In my location table, I know which place is outside or not. Below query gives me people who are inside. If I make isOutside = 1, it gives me people who are outside. So the problem is that a person can have entries where isOutside is equal to 1 or 0. How can I differentiate people who have isOutside value 0 but don't have any entry where isOutside is equal to 1.

SELECT DISTINCT(macID)
FROM locations a, logs b
WHERE b.location_id = a.id and b.client_id=1 and Date(b.lastLocatedTime) =  '2015-01-16'
and a.isOutside =0 and b.client_id = a.client_id

Update

I wrote this query which worked for me. It is similar to Bohemian's answer.

SELECT COUNT(DISTINCT macID)
FROM logs
WHERE location_id IN (SELECT id FROM locations WHERE isOutside = 0) AND client_id = 1 AND
                        DATE(lastLocatedTime) = '2015-01-16' AND macID NOT IN 
                        (SELECT macID 
                        FROM logs 
                        WHERE DATE(lastLocatedTime) = '2015-01-16' AND
                        location_id IN (SELECT id FROM locations WHERE isOutside = 1))

Answer 1

Use a NOT IN test:

SELECT DISTINCT(macID)
FROM locations a
JOIN logs b ON a.id = b.location_id AND a.client_id = b.client_id
WHERE b.client_id=1 and Date(b.lastLocatedTime) =  '2015-01-16'
AND a.client_id NOT IN (SELECT client_id FROM locations WHERE isOutside = 1)

Answer 2

Use a left join to outsiders and filter out joins, leaving just insiders:

SELECT DISTINCT l.macID
FROM logs l
JOIN locations a ON l.location_id = a.id
  AND l.client_id = a.client_id
  AND a.isOutside = 0
LEFT JOIN (SELECT macId, l2.client_id, date(lastLocatedTime) lastLocatedDate
           FROM logs l2
           JOIN locations a2 ON l2.location_id = a2.id
           AND l2.client_id = a2.client_id
           AND a2.isOutside = 1) o
  ON o.client_id = l.client_id
  AND o.macID = l.macID
  AND lastLocatedDate = Date(l.lastLocatedTime)
WHERE Date(l.lastLocatedTime) = '2015-01-16'
AND o.client_id IS NULL
AND l.client_id = 1

See SQLFiddle

Here, logs is inner joined to location to find all insiders, but then outer joined to outsiders, which if not found will contain all nulls that the where clause selects (rejecting joins that were successful).

Also DISTINCT is not a function, so prefer not coding it as one; ie DISTINCT macID , not DISTINCT(macID) .