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I am trying to select two columns from two different tables, where a value exists in both tables and the time in one table is >= now - 30 minutes. How ever it is returning all the firstnames and then inserting the same time for all names?

Here is the schema for the two tables;

CREATE TABLE probes (
  mac_address TEXT,
  vendor TEXT,
  ssid TEXT,
  date_Stamp NUMERIC,
  time_Stamp NUMERIC,
  rssi INTEGER,
  bssid TEXT
)

CREATE TABLE `studentDetails` (
  studentID INTEGER UNIQUE,
  firstName TEXT,
  lastName TEXT,
  macAddress TEXT,
  pictureLocation TEXT,
  PRIMARY KEY(studentID)
)

Finally here is my query:

SELECT time_Stamp, firstName
FROM probes
INNER JOIN studentDetails
WHERE EXISTS (
       select     mac_address 
       from probes 
       where     mac_address =     studentDetails.macAddress) 
AND time_Stamp >= time('now') 
GROUP BY firstName

However returning:

"14:52:16" "Andrew"

"14:52:16" "Hanna "

"14:52:16" "Liam "

Even though only one of those users has that time?

Any help would be much appreciated.

"14:52:16" "Sarah"

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