aassignment01-Yanyang Chen

README.md

@@ -73,34 +73,44 @@ Write a query to answer each of the questions below.
 
     **Result:** 300,432
 
-2. [What is the percent change in trips in Q3 2022 as compared to Q3 2021?](query02.sql)
-
+2. [What is the percent change in trips in Q3 2022 as compared to Q3 2021?](query02.sql) 
+Result: 3.98%
 3. [What is the average duration of a trip for 2021?](query03.sql)
-
+18.86 minutes
 4. [What is the average duration of a trip for 2022?](query04.sql)
-
+17.88 minutes
 5. [What is the longest duration trip across the two quarters?](query05.sql)
+1440mins
 
     _Why are there so many trips of this duration?_
 
-    **Answer:**
+    **1440 minutes equals exactly 24 hours. This likely indicates bikes that were not returned on time or were checked out but not properly closed in the system. The system may have a default maximum duration of 24 hours for billing purposes, causing all overdue rentals to be capped at this duration. This could also represent data anomalies or system errors where bike checkouts were not properly recorded as completed.**
 
 6. [How many trips in each quarter were shorter than 10 minutes?](query06.sql)
-
+Q3 2021: 27,121 trips
+Q3 2022: 28,122 trips
 7. [How many trips started on one day and ended on a different day?](query07.sql)
-
+Q3 2021: 2,301 trips
+Q3 2022: 2,060 trips
 8. [Give the five most popular starting stations across all years between 7am and 9:59am.](query08.sql)
-
-    _Hint: Use the `EXTRACT` function to get the hour of the day from the timestamp._
-
+Station 3032: 1,828 trips
+Station 3102: 1,689 trips
+Station 3012: 1,614 trips
+Station 3066: 1,529 trips
+Station 3007: 1,434 trips
 9. [List all the passholder types and number of trips for each across all years.](query09.sql)
-
+Indego30: 441,856 trips
+Indego365: 109,251 trips
+Day Pass: 61,659 trips
+NULL: 43 trips
+Walk-up: 2 trips
 10. [Using the station status dataset, find the distance in meters of each station from Meyerson Hall.](query10.sql)
-
+All 293 stations with their distances from Meyerson Hall (in meters, rounded to nearest 50m)
 11. [What is the average distance (in meters) of all stations from Meyerson Hall?](query11.sql)
-
+Result: 3 km (approximately 3,000 meters)
 12. [How many stations are within 1km of Meyerson Hall?](query12.sql)
-
+Result: 18 stations
 13. [Which station is furthest from Meyerson Hall?](query13.sql)
-
+Manayunk & Conarroe, Fairview Park (Station ID: 3432) - 9,000 meters (9 km away)
 14. [Which station is closest to Meyerson Hall?](query14.sql)
+34th & Spruce (Station ID: 3208)

query02.sql

@@ -12,7 +12,6 @@
 -- Enter your SQL query here
 
 
-
 /*
     If you want to get fancier here, you can cast the result to a string and
     concatenate a '%' to the end. For example:
@@ -22,3 +21,16 @@
     This uses the type casting (number to string) and string concatenation
     operator (`||`, double pipes) that's essentially a `+` for strings.
 */
+
+
+SELECT
+    CAST(
+        ROUND(
+            CAST(
+                (((SELECT COUNT(*) FROM indego.trips_2022_q3) - (SELECT COUNT(*) FROM indego.trips_2021_q3)) / CAST((SELECT COUNT(*) FROM indego.trips_2021_q3) AS FLOAT)) * 100
+                AS NUMERIC
+            ),
+            2
+        )
+        AS FLOAT
+    ) AS perc_change;

query03.sql

@@ -6,3 +6,5 @@
 */
 
 -- Enter your SQL query here
+SELECT ROUND(AVG(duration), 2) AS avg_duration
+FROM indego.trips_2021_q3;

query04.sql

@@ -6,3 +6,6 @@
 */
 
 -- Enter your SQL query here
+
+SELECT ROUND(AVG(duration), 2) AS avg_duration
+FROM indego.trips_2022_q3;

query05.sql

@@ -5,3 +5,9 @@
 */
 
 -- Enter your SQL query here
+SELECT MAX(duration) AS max_duration
+FROM (
+    SELECT duration FROM indego.trips_2021_q3
+    UNION ALL
+    SELECT duration FROM indego.trips_2022_q3
+) AS combined_trips;

query06.sql

@@ -7,3 +7,18 @@
 */
 
 -- Enter your SQL query here
+SELECT
+    2021 AS trip_year,
+    'Q3' AS trip_quarter,
+    COUNT(*) AS num_trips
+FROM indego.trips_2021_q3
+WHERE duration < 10
+
+UNION ALL
+
+SELECT
+    2022 AS trip_year,
+    'Q3' AS trip_quarter,
+    COUNT(*) AS num_trips
+FROM indego.trips_2022_q3
+WHERE duration < 10;

query07.sql

@@ -8,7 +8,6 @@
 -- Enter your SQL query here
 
 
-
 /*
 
     Hint 1: when you cast a TIMESTAMP to a DATE the time component of the value is simply stripped off
@@ -17,3 +16,18 @@
     [EXTRACT](https://www.postgresql.org/docs/12/functions-datetime.html#FUNCTIONS-DATETIME-EXTRACT)
     function.
 */
+SELECT
+    2021 AS trip_year,
+    'Q3' AS trip_quarter,
+    COUNT(*) AS num_trips
+FROM indego.trips_2021_q3
+WHERE CAST(start_time AS DATE) != CAST(end_time AS DATE)
+
+UNION ALL
+
+SELECT
+    2022 AS trip_year,
+    'Q3' AS trip_quarter,
+    COUNT(*) AS num_trips
+FROM indego.trips_2022_q3
+WHERE CAST(start_time AS DATE) != CAST(end_time AS DATE);

query08.sql

@@ -15,3 +15,20 @@
     Hint: Use the `EXTRACT` function to get the hour of the day from the
     timestamp.
 */
+SELECT 
+    s.id AS station_id,
+    s.geog AS station_geog,
+    COUNT(*) AS num_trips
+FROM (
+    SELECT start_station FROM indego.trips_2021_q3
+    WHERE EXTRACT(HOUR FROM start_time) >= 7 
+      AND EXTRACT(HOUR FROM start_time) < 10
+    UNION ALL
+    SELECT start_station FROM indego.trips_2022_q3
+    WHERE EXTRACT(HOUR FROM start_time) >= 7 
+      AND EXTRACT(HOUR FROM start_time) < 10
+) trips
+JOIN indego.station_statuses s ON CAST(trips.start_station AS INTEGER) = s.id
+GROUP BY s.id, s.geog
+ORDER BY num_trips DESC
+LIMIT 5；

query09.sql

@@ -7,3 +7,13 @@
 */
 
 -- Enter your SQL query here
+SELECT
+    passholder_type,
+    COUNT(*) AS num_trips
+FROM (
+    SELECT passholder_type FROM indego.trips_2021_q3
+    UNION ALL
+    SELECT passholder_type FROM indego.trips_2022_q3
+) AS combined_trips
+GROUP BY passholder_type
+ORDER BY num_trips DESC;

query10.sql

@@ -8,3 +8,13 @@
 */
 
 -- Enter your SQL query here
+
+SELECT
+    id AS station_id,
+    geog AS station_geog,
+    ROUND(ST_DISTANCE(
+        geog,
+        ST_SETSRID(ST_MAKEPOINT(-75.192584, 39.952415), 4326)::GEOGRAPHY
+    ) / 50) * 50 AS distance
+FROM indego.station_statuses
+ORDER BY distance ASC;

query11.sql

@@ -5,3 +5,11 @@
 */
 
 -- Enter your SQL query here
+SELECT
+    ROUND(AVG(
+        111.111 * SQRT(
+            POWER(lat - 39.952415, 2)
+            + POWER((lon - (-75.192584)) * COS(RADIANS(lat)), 2)
+        )
+    )) AS avg_distance_km
+FROM indego.station_statuses;

query12.sql

@@ -6,3 +6,9 @@
 */
 
 -- Enter your SQL query here
+SELECT COUNT(*) AS num_stations
+FROM indego.station_statuses
+WHERE ST_DISTANCE(
+    geog,
+    ST_SETSRID(ST_MAKEPOINT(-75.192584, 39.952415), 4326)::GEOGRAPHY
+) < 1000;

query13.sql

@@ -7,3 +7,14 @@
 */
 
 -- Enter your SQL query here
+
+SELECT
+    id AS station_id,
+    name AS station_name,
+    ROUND(111.111 * SQRT(
+        POWER(lat - 39.952415, 2)
+        + POWER((lon - (-75.192584)) * COS(RADIANS(lat)), 2)
+    ) * 1000 / 50) * 50 AS distance
+FROM indego.station_statuses
+ORDER BY distance DESC
+LIMIT 1;

query14.sql

@@ -7,3 +7,13 @@
 */
 
 -- Enter your SQL query here
+SELECT
+    id AS station_id,
+    name AS station_name,
+    ROUND(111.111 * SQRT(
+        POWER(lat - 39.952415, 2)
+        + POWER((lon - (-75.192584)) * COS(RADIANS(lat)), 2)
+    ) * 1000 / 50) * 50 AS distance
+FROM indego.station_statuses
+ORDER BY distance ASC
+LIMIT 1;