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Время

Термометр, 36.6

10:43, Термометр, 36.6

Время Термометр
10:43 36.6

Время Термометр Барометр
10:43 36.6 null
10:48 36.7 180

Таблица baro
time  Value.
Таблица termo
Time Value.

Select baro.Time, baro.Value, termo.Value from baro, termo where baro.time = termp.time;

select * from baro, termo, hermo group by time

Cursor c = sqlExec("SELECT time DISTINCT(time) FROM mainTable ");
while(c.hasNext()){
sqlExec("SELECT * FROM mainTable WHERE device = c.device" GROUP BY time)
}

query = "SELECT timeTbl.Time AS [TIME], ";
for (int i = 0; i < devices.size(); ++i)        //использовать лучше foreach
{
    query += QString("device%1.Value AS [%2], ").arg(i).arg(devices.at(i))
}

query += "FROM mainTable as timeTbl "

for (int i = 0; i < devices.size(); ++i)
{
    QString subQuery ("SELECT Time, Value From mainTable WHERE Device = %1").arg(devices.at(i))
    query += QString("LEFT JOIN (%1) AS device%2 ON  (timeTbl.Time= device%2.Time) ").arg(subQuery).arg(i);
}

query += GROUP BY timeTbl.Time

SELECT DISTINCT mainTable.Time, barometer.Value as BAROMETER, thermometer.Value as THERMOMETER
FROM (mainTable 

LEFT JOIN (SELECT mainTable.Time, mainTable.Value
                  FROM mainTable
                  WHERE mainTable.Device="barometer") AS barometer ON barometer.Time = mainTable.Time)

LEFT JOIN (SELECT mainTable.Time, mainTable.Value
                  FROM mainTable
                  WHERE mainTable.Device="thermometer") AS thermometer ON thermometer.Time = mainTable.Time