You don't want to do that. You are using a function of your Start_time
column in your comparison. That prevents the use of any index on
Start_time, so a full-table scan will be required. Always compare a column
to a constant (or a range), if at all possible. Fortunately, that's easy in
this case:
SELECT Start_time, End_time FROM Table
WHERE Start_time >= NOW() - INTERVAL 4 HOUR;
Michael
Viswanatha Rao wrote:
Thanks.
I used
SELECT Start_time, End_time FROM Table WHERE Start_time - DATE_SUB(
NOW(), INTERVAL 4 HOUR ) >=0
It works.
-----Original Message-----
From: Wesley Furgiuele [mailto:[EMAIL PROTECTED]
Sent: Wednesday, August 18, 2004 3:11 PM
To: Viswanatha Rao
Cc: [EMAIL PROTECTED]
Subject: Re: select rows by compare on datetime column - more on time
decrement
What version of MySQL are you using? You have different options.
http://dev.mysql.com/doc/mysql/en/Date_and_time_functions.html
Look at DATE_SUB() and SUBDATE()/SUBTIME().
The time part of the query would look something like DATE_FORMAT(
DATE_SUB( NOW(), INTERVAL 4 HOUR ), '%H:%i:%s' ), or something like
that.
Or, this might be better handled in Perl, just using Perl to control
the time value supplied in the query -- I'm not sure about your "and so
on". I wouldn't know how to handle a series of t1, t2, t3, t4, ..., tn
without use of a scripting/programming language.
Wes
On Aug 18, 2004, at 3:44 PM, Viswanatha Rao wrote:
I have to select mysql rows based on the following condition.
Time t1 = (current time - 4 hours);
Time t2 = (current time - 8 hours);
In my case, I want to select all those rows that have start times
(1) between current time and t1
(2) between time t1 and t2
... and so on
So I have to somehow subtract hours from the current time to get t1,
t2,
and so on. In some other cases, I may have to subtract specific number
of minutes.
So my question is how do I selectively subtract hours or minutes from
current time in mysql.
I need these values to plot a chart. Please let me know?
-----Original Message-----
From: Wesley Furgiuele [mailto:[EMAIL PROTECTED]
Sent: Wednesday, August 18, 2004 11:36 AM
To: Viswanatha Rao
Cc: [EMAIL PROTECTED] List
Subject: Re: select rows by compare on datetime column
Vishwa:
Sorry -- I used a specific time value as an example, but since you
were
asking about current time, you would use CURTIME():
SELECT columns FROM table WHERE DATE_FORMAT( start_time, '%H:%i:%s' )
= CURTIME() AND DATE_FORMAT( end_time, '%H:%i:%s' ) <= CURTIME();
Wes
On Aug 18, 2004, at 12:24 PM, Wesley Furgiuele wrote:
Does the date matter, or only the time?
If date matters (you want to find all records between 2004-06-01
10:00:00 AND 2004-06-03 18:00:00):
SELECT columns FROM table WHERE start_time >= '2004-06-01 10:00:00'
AND end_time <= '2004-06-03 18:00:00'
If only time matters( you want to find all records between 10:00:00
AND 18:00:00 on any day):
--> If you're using version 4.1.1 or greater:
SELECT columns FROM table WHERE TIME( start_time ) >= '10:00:00' AND
TIME( end_time ) >= '18:00:00'
--> Otherwise:
SELECT columns FROM table WHERE DATE_FORMAT( start_time, '%H:%i:%s' )
= '10:00:00' AND DATE_FORMAT( end_time, '%H:%i:%s' ) <= '18:00:00'
Wes
On Aug 18, 2004, at 11:39 AM, Viswanatha Rao wrote:
I have two columns in a table: start_time and end_time. Both are of
types DATETIME
When I select rows from table, I want to select only those rows
where
the current time falls between start_time and end_time
Can someone help with the SELECT syntax for this?
Best Regards
Vishwa Rao
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