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+/************ Common Table Expression and Recursion *************/
+
+/* CTE is basically a way of creating Temporary Table */
+
+/* daily average temp */
+WITH daily_average_temp AS(
+SELECT DATE_TRUNC('day', event_time) AS event_date,
+AVG(temp_celcius) AS avg_temp
+FROM time_series.location_temp
+GROUP BY DATE_TRUNC('day', event_time)
+)
+SELECT event_date, avg_temp
+FROM daily_average_temp;
+
+

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+/****** Calculating Aggregates over windows *******/
+
+SELECT server_id,cpu_utilization,
+AVG(cpu_utilization) OVER (PARTITION BY server_id)
+FROM time_series.utilization
+WHERE event_time BETWEEN '2019-03-05' AND '2019-03-06';

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+/***** Comparison (comparing to Previous Period) ********/
+
+-- will compare the avg temp of current day with avg temp of previous day
+-- based on this, we can do comparison of month to month, year to year, etc.
+WITH avg_daily_temp AS(
+SELECT
+DATE_TRUNC('day', event_time) AS event_day,
+AVG(temp_celcius) AS avg_temp
+FROM time_series.location_temp
+GROUP BY DATE_TRUNC('day', event_time)
+)
+SELECT
+d1.event_day, d1.avg_temp,
+(SELECT d2.avg_temp
+FROM avg_daily_temp d2
+WHERE d2.event_day = d1.event_day - INTERVAL '1' day)
+FROM avg_daily_temp d1;