Cleaning and analyzing employee data
Question
Below is a snippet from a table that contains information about employees that work at Company XYZ:
| employee_name | employee_id | date_joined | age | yrs_of_experience |
|---|---|---|---|---|
| Andy | 123456 | 2015-02-15 | 45 | 24 |
| Beth | 789456 | NaN | 36 | 15 |
| Cindy | 654123 | 2017-05-16 | 34 | 14 |
| Dale | 963852 | 2018-01-15 | 25 | 4 |
Company XYZ recently migrated database systems causing some of the date_joined records to be NULL. You're told by an analyst in human resources NULL records for the date_joined field indicates the employees joined prior to 2010. You also find out there are multiple employees with the same name and duplicate records for some employees.
Given this, write code to find the number of employees that joined each month. You can group all of the null values as Dec 1, 2009.
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