SQL Comparing Dates - mysql

Question

in a database table I have made a date attribute but I have set it's type to varchar and not Date.
My question is, will I still be able to compare such dates in a SQL Query?
Dates in my DB are stored in this format:
dd/mm/yyyy hh:mm:ss
I have to do a SQL Query in PHP that looks something like this:
SELECT *
FROM DBtable
WHERE DBname='$name' AND date>='01/01/2015' AND date<='01/09/2015';
I would appreciate an example how to do this.
Thank you for your help.

Answer 1

You'll need to convert/cast to compare:
SELECT *
FROM DBtable
WHERE DBname='$name'
AND CAST(date AS DATETIME) >='2015-01-01'
AND CAST(date AS DATETIME)<='2015-01-09'
;
Much better to store values as the appropriate data types to avoid this inefficiency. You could also use DATE instead of DATETIME if you want to compare without the time component. Syntax and available datatypes vary by database, so the above may need adjustment.
Update: Since you're using MySQL, you can use the following:
SELECT *
FROM DBtable
WHERE DBname='$name'
AND STR_TO_DATE(`date`, '%d/%c/%Y') >= '2015-01-01'
AND STR_TO_DATE(`date`, '%d/%c/%Y') <= '2015-01-09'
;

Answer 2

Yes you can cast a Varchar to a Date. Here is an example:
SELECT
CAST(date_column AS DATETIME)
FROM
TABLE_NAME
In your case it might look like:
SELECT *
FROM DBtable
WHERE DBname='$name'
AND CAST(date AS DATETIME) >='01/01/2015'
AND CAST(date AS DATETIME) <='01/09/2015';

Answer 3

You can cast or convert a varchar to a date or datetime before you do any comparisons.
But you'd have to do it every single time you compare the date to something. That's because the following comparisons are all true if you compare them as varchar:
'2/1/2015' > '1/5/2016'
'25/1/2015' > '15/2/2015'
'11/1/2015' < '3/1/2015'
You'll also need to convert if you want to pull out some time-based aspect of the dates, such as any records where the hour was before 8:00 AM. There is no easy way to do that if your date is a varchar.
And that assumes that the value in your database can always be parsed into a date! If an empty string or some other kind of data gets in there, CONVERT(datetime, MyColumn) will fail.
So I would strongly recommend that you change your column to be a date or datetime. It will make your life much easier.