Question

I’m trying to make some vchar values searchable based on a date.

The strings I have to work with look like this:

1/7/2006 12:45:24 AM

1/7/2006 1:18:36 AM

1/7/2006 1:21:43 AM

1/7/2006 1:32:09 AM

3/30/2006 12:32:10 PM

3/30/2006 1:19:30 PM

3/30/2006 1:20:44 PM

So first off let’s get rid of the AM.. PHPMyAdmin the sql query is:

 SELECT  trim('AM'  FROM  `orderdate`) FROM tblorders

This works to get rid of the AM now let’s set the values as a variable and try to wrap a string to str_to_date() around the results:

SELECT  trim('AM'  FROM  `orderdate`) AS `value`, STR_TO_DATE(`value`,'%d,%m,%Y') FROM tblorders

This yields value as an unknown column. How else do you string two function values together so as to then use them to be filtered such as WHERE value > 2/1/2006 ?

Answer 1

You can compose functions like this:

select str_to_date(trim('AM' from orderdate), '%m/%d/%Y')

Note that I also corrected your date format to match your data. You don’t actually need to trim those values to use str_to_date on them, just this will work fine:

select str_to_date(orderdate, '%m/%d/%Y')

If you want to use that in your WHERE clause then put the function calls in there:

select trim('AM' from orderdate), str_to_date(orderdate, '%m/%d/%Y')
from your_table
where str_to_date(orderdate, '%m/%d/%Y') > '2006-01-02'

and let the optimizer recognize the repetition or use a derived table:

select value, the_date
from (
    select trim('AM' from orderdate) as value, str_to_date(orderdate, '%m/%d/%Y') as the_date
    from your_table
) dt
where the_date > '2006-01-02'

Note the use of ISO 8601 dates in the query, that format is unambiguous and any database worth using will understand it regardless of your locale settings.

I’d also recommend that you fix your schema to use real timestamps instead of those strings.