Ask the indexing problem of date string in mysql

one of my data tables has a creation time field (timestamp) and a date string: 2018.12.10 this is mainly because there is a query on the front end that is queried by day, so the date string is saved and indexed.
think that there is another way to query, that is, convert the date to a timestamp, calculate the start and end timestamps, and then check the records whose creation time is greater than the start and less than the end. So I don"t need the date string field.
I wonder which of these two ways is better? Thank you

Php
Feb.09,2022

if there is a condition for querying days, the quickest way is to establish a separate field, one date, and one is to store the int field of day. The query efficiency of integer type is relatively high

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