diff --git a/internal/dao/sensor.go b/internal/dao/sensor.go
index 82fbe7d..98bc5d6 100644
--- a/internal/dao/sensor.go
+++ b/internal/dao/sensor.go
@@ -47,7 +47,7 @@ func (dao *SensorDAO) GetAggregatedData(start, end time.Time, interval string) (
 	case "5min":
 		query = `
             SELECT 
-                DATE_FORMAT(timestamp, '%Y-%m-%d %H:%i:00') as ts,
+                MIN(timestamp) as ts,
                 ROUND(AVG(temperature)/10, 1) as avg_temp,
                 MAX(rainfall) - MIN(rainfall) as rainfall,
                 ROUND(AVG(humidity)/10, 1) as avg_humidity,
@@ -60,7 +60,7 @@ func (dao *SensorDAO) GetAggregatedData(start, end time.Time, interval string) (
 	case "30min":
 		query = `
             SELECT 
-                DATE_FORMAT(timestamp, '%Y-%m-%d %H:%i:00') as ts,
+                MIN(timestamp) as ts,
                 ROUND(AVG(temperature)/10, 1) as avg_temp,
                 MAX(rainfall) - MIN(rainfall) as rainfall,
                 ROUND(AVG(humidity)/10, 1) as avg_humidity,
@@ -73,14 +73,14 @@ func (dao *SensorDAO) GetAggregatedData(start, end time.Time, interval string) (
 	default: // 1hour
 		query = `
             SELECT 
-                DATE_FORMAT(timestamp, '%Y-%m-%d %H:00:00') as ts,
+                MIN(timestamp) as ts,
                 ROUND(AVG(temperature)/10, 1) as avg_temp,
                 MAX(rainfall) - MIN(rainfall) as rainfall,
                 ROUND(AVG(humidity)/10, 1) as avg_humidity,
                 ROUND(AVG(wind_speed)/10, 1) as avg_wind_speed
             FROM sensor_data 
             WHERE timestamp BETWEEN ? AND ?
-            GROUP BY DATE_FORMAT(timestamp, '%Y-%m-%d %H')
+            GROUP BY FLOOR(UNIX_TIMESTAMP(timestamp)/3600)
             ORDER BY ts DESC
         `
 	}