OP18: Counts of observation period records stratified by start of observation month

This query is used to count the observation period records stratified by observation month and person end. person end is an indicator whether a person has initiated the first observation period in a given observation month. All possible values are summarized.

Input:
<None>

Sample query run:
The following is a sample run of the query.
SELECT EXTRACT( month FROM observation_period_start_date ) observation_month
     , count(*) AS num_observations
  FROM observation_period
GROUP BY EXTRACT( month FROM observation_period_start_date )
ORDER BY 1
Output:
Output field list:
 Field  Description
observation_month Month of start of observation period
num_observations Number of observations within specific month of observation

Sample output record:
 Field  Description
observation_month  1
num_observations  3987706
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