Sql Query To Return Nil For Dates Not Present In The Table

I have a table 'my_table'. It has the following data : ID --- Date 1 --- 01/30/2012 2 --- 01/30/2012 3 --- 05/30/2012 I can write a SQL query to re

Solution 1:

The way I do it is to have a static table with list of all the dates. In your case that's 30th of each month (what about February?). Lets call this table REF_DATE. It has a single column DT that holds the date.

Assuming that my_table only contains 0 or at most 1 distinct date (30th) in each month, what you need to do is:

select DT,count(ID) from 
REF_DT REFleftouterjoin my_table MT 
on REF.DT=my_table.DATE
groupby REF.DT;

Solution 2:

I came up with somewhat hackish way through rails

classMonth<Date   # for getting months in rangedefsuccself >> 1endend

range = Month.new(2010,1,1)..Month.new(2013,1,1) # range of date to query
months=Hash.new
(range).each do|month|
  months.merge!({month.to_s => 0}) # get all months as per range requirement of projectend

db_months = MyTable.find_all_by_date(range).group_by{ |u| u.date.beginning_of_month }.map{|m,v| [m.to_s , v.size]} #get all records grouped by months

all_months = months.merge(Hash[db_months]) # merge all missing months

Replace the range with the dates you want also the format of the date as per your requirement.

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