Mysql implicit conversion when comparing date column and datetime/time string - mysql

Question

I have a table with a Date column. It has a row where my_date column's value is 2017-11-24
SELECT * FROM mytable WHERE my_date = '2017-11-24 00:00:00' returns that row.
While SELECT * FROM mytable WHERE my_date = '2017-11-24 00:00:01' does not.
From mysql doc; this page says
If one of the arguments is a TIMESTAMP or DATETIME column and the
other argument is a constant, the constant is converted to a timestamp
before the comparison is performed. This is done to be more
ODBC-friendly. This is not done for the arguments to IN().
If I am interpreting this correctly, in the second query, the constant on right side would be implicitly casted to Date field
The second page for casting says -
Conversion to a DATE value takes fractional seconds into account and
rounds the time part. For example, '1999-12-31 23:59:59.499' becomes
'1999-12-31', whereas '1999-12-31 23:59:59.500' becomes '2000-01-01'.
The example shows 1999-12-31 23:59:59.499 -> 1999-12-31. I understand explicit casting is preferred, but I am wondering why mysql chose to typecast the column value instead of constant or if there's something else happening here.

Answer 1

I don't think you are interpreting the docs correctly. The first page you quote is about comparing a DATETIME or TIMESTAMP to a constant. You are comparing a DATE to a constant, so this logic should apply:
Conversion of DATE values:
Conversion to a DATETIME or TIMESTAMP value adds a time part of '00:00:00' because the DATE value contains no time information.
So it's like comparing '2017-11-24 00:00:00' = '2017-11-24 00:00:01' which sensibly returns false.
Comparing DATEs to DATETIMEs/TIMESTAMPs is similar to comparing an int to a double in that the implicit conversion applies to the less precise value. You would not expect 42 to match 42.1, and likewise you shouldn't expect 2017-11-24 to match 2017-11-24 00:00:01.