MySQL: Get the datetime field with time part reset to midnight (00:00:00)?

I am trying to query the PurchaseDate datetime column from tmp table along with a custom column that is PurchaseDate column with time as 00:00:00 / midnight:

I wasn’t able to do it using DATEDIFF(). How can I do it in the simplest way?

As suggested, I have tried using date(). However that converts the column type to date and I would like to retain it as a datetime.

Answers:

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Method 1

Convert to date to truncate the time part, then cast to datetime:

select
    PurchaseDate,
    cast(date(PurchaseDate) as datetime) as StartOfDay
from mytable

See live demo.

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