What's the best way to select all records of a specific date in Sequel ignoring the time?
Writing a where clause with range from the day's 0 to 23:59 seems to unlike it. Any other way to do?
Use:
Post.where(:created_at => (date.beginning_of_day..date.end_of_day))
where date is the Date object
Related
Say I have two timestamp type columns timestamp_column1 and timestamp_column2
I want to compare if timestamp_column1 is greater than timestamp_column2.
How do I compare these two timestamps ? Does comparison operators work properly with timestamp on Oracle?
timestamp_column1 > timestamp_column2
Is this correct??
Or do I have to wrap them in some function to compare them with each other
like to_timestamp(timestamp_column1) > to_timestamp(timestamp_column2)
?
As long as the "timestamp" columns are truly using one of the date or timestamp data types, then yes the usual relational operators will work.
The only time you need to wrap a timestamp in a function is if it's erroneously stored as a string, or if you want to manipulate it in some way such as truncating it to the hour, day, week, month, year or other less discreet unit of time.
I have 3 columns in my mongodb named as days (long), startDate (java.util.Date), endDate (java.util.Date). What all I want to fetch the records between startDate and (endDate-days) OR (endDate-startDate) <= days.
Can you please let me know how could i achieve this using mongoTemplate spring.
I don't want to fetch all the records from table and then resolve this on java side since in future my table may have million of records.
Thanks
Jitender
There is no way to do this in the query on the DB side (the end minus start part). What I recommend if this is an important feature for your application is that you alter the schema to maintain in the document the delta between the two fields in the format you need it. Since you can update that field when you update endDate (or if you populate both dates at the same time you can just compute the field then).
If you receive this data in bulk from another source, or if you do multi-updates of the endDate then you will probably need another job to run and periodically compute the delta of the documents where it's not computed (then you can start with always setting delta to 99999 and update it in this job to accurate value once endDate is set).
While you can use $where clause, it will be a very slow full collection scan so I would not suggest its use - it's probably better to come up with a more performant alternative even if it requires altering the schema.
http://docs.mongodb.org/manual/reference/operator/where/
I would like to get the records that have their created_at date closest to the current date. How can I do this with active records' where clause?
You could find the closest record in the past with something like:
Record.where("created_at <= ?", Date.today).order_by("created_at DESC").limit(1)
Similarly, you can have the closest record in the future
Record.where("created_at >= ?", Date.today).order_by("created_at ASC").limit(1)
And then compare wich one is the closest to current date...
There may be a solution to do it with a single request, but I could not find how (if you're using SQL server, there's a method DATEDIFF that could help).
Update: Thanks to Mischa
If you're sure that all created_atare in the past, you're looking to the last created record, that could be written
Record.order("created_at").last
Update
To get all the records created the same date then the last record:
last_record_date = Record.max(:created_at)
Record.where(:created_at => (last_record_date.at_beginning_of_day)..(last_record_date.end_of_day))
I have last_update_date column defined as DATE field
I want to get time in milliseconds.
Currently I have:
TO_CHAR(last_update_date,'YYYY-DD-MM hh:mi:ss am')
But I want to get milliseconds as well.
I googled a bit and think DATE fields will not have milliseconds. only TIMESTAMP fields will.
Is there any way to get milliseconds? I do not have option to change data type for the field.
DATE fields on Oracle only store the data down to a second so there is no way to provide anything more precise than that. If you want more precision, you must use another type such as TIMESTAMP.
Here is a link to another SO question regarding Oracle date and time precision.
As RC says, the DATE type only supports a granularity down to the second.
If converting to TIMESTAMP is truly not an option then how about the addition of another numerical column that just holds the milliseconds?
This option would be more cumbersome to deal with than a TIMESTAMP column but it could be workable if converting the type is not possible.
In a similar situation where I couldn't change the fields in a table, (Couldn't afford to 'break' third party software,) but needed sub-second precision, I added a 1:1 supplemental table, and an after insert trigger on the original table to post the timestamp into the supplemental table.
If you only need to know the ORDER of records being added within the same second, you could do the same thing, only using a sequence as a data source for the supplemental field.
I could use this query to select all orders with a date on a monday:
SELECT * from orders WHERE strftime("%w", date)="1";
But as far as I know, this can't be speed up using an index, as for every row strftime has to be calculated.
I could add an additional field with the weekday stored, but I want to avoid it. Is there a solution that makes use of an index or am I wrong and this query actually works fine? (That means it doesn't have to go through every row to calculate the result.)
If you want all Mondays ever, you'd need a field or sequential scan. What you could do, is calculate actual dates for example for all Mondays within a year. The condition WHERE date IN ('2009-03-02', '2009-02-23', ...) would use index
Or as an alternative to vartec's suggestion, construct a calendar table consisting only of a date and a day name for each day in the year (both indexed) and then perform your query by doing a JOIN against this table.