How to calculate the difference between two year-month periods using the PERIOD_DIFF() function?

PERIOD_DIFF(P1, P2) is a MySQL built-in function that calculates the difference between two year-month periods. For example:

SELECT PERIOD_DIFF(201802, 201703), PERIOD_DIFF(201703, 201802);
  -- +-----------------------------+-----------------------------+
  -- | PERIOD_DIFF(201802, 201703) | PERIOD_DIFF(201703, 201802) |
  -- +-----------------------------+-----------------------------+
  -- |                          11 |                         -11 |
  -- +-----------------------------+-----------------------------+

Reference information of the PERIOD_DIFF() function:

PERIOD_DIFF(P1, P2): int
  Returns the number of months between periods P1 and P2. P1 and P2
  should be in the format YYMM or YYYYMM.

Arguments, return value and availability:
  P1: Required. The year-month period to be subtracted from.
  P2: Required. The year-month period to be subtracted.
  int: Return value. The difference in months.
  Available since MySQL 4.

Related MySQL functions:

• PERIOD_ADD() - Adding Months to Period

⇒ QUARTER() - Quarter of Year

⇐ PERIOD_ADD() - Adding Months to Period

⇑ MySQL Functions on Date and Time

⇑⇑ MySQL Function References