Question

I have a DATETIME string and I need only the DATE in my script to perform some searches in my database. Currently, I have two scenarios in my mind, but don’t know which of them is faster.

The first scenario:

In my MYSQL database, I have two columns: datetime (which is a DATETIME type) and date (which is a DATE type).

Then, in my PHP script, each time I save a record, I will insert my known string to the datetime field, and then convert it to fit the date field (I was thinking of something like: $date = date("Y-m-d", strtotime($datetime))).

This way, all the necessary pieces are stored in my database and I can retrieve them on the fly (both the datetime and the date fields).

The second scenario:

The MYSQL database should consist only of the datetime column.

My PHP script will insert the known string to the datetime field without any other modifications.

And when I retrieve my data, I would do something like: SELECT datetime, DATE(datetime) FROM ...

Conclusion

Which of these scenarios is faster and therefore should be used? Should date formats be made on save or on retrieve? Is MYSQL faster than PHP on formatting dates? Is it better to store everything in the database and retrieve as it is, or store only the minimum and format on retrieve? Which of these scenarios is the best practice?

Thank you!

Answer 1

It depends of your usecases:

If you are only going to need the date for reading, then go with a single datetime column, conversion from datetime to date is cheap enough.

If you are going to select rows at a given date (like WHERE date = '2011-08-01'), then go for a date column, as this will allow mysql to use the indexes on the date column if you have added one.

If you are going to select rows in a date range, then go for a datetime column. You could do things like WHERE datetime >= '2011-08-01' AND datetime < '2011-08-16'.