Question

I have these two tables:

DateRanges

some_id   start_date    end_date
---------------------------------
1         2012-12-01   2012-12-15
1         2013-01-01   2013-01-15
3         2013-01-03   2013-01-10


Items

id      name
----------------
1     Some name
2     Other name
3     So on...

What I try to achieve is to get, for each element in Items table, the biggest start_date (ignoring the smaller dates/date ranges for that Item) and check if the current date is in that range, like in the next table (let’s say today’s 02 January 2013):

id       name          TodayIsInTheRange
---------------------------------------------
1      Some name             true
2      Other name            false
3      So on...              false

I have tried to obtain the 3rd table with the next query:

SELECT A.*, (B.`start_date` <= CURRENT_DATE AND CURRENT_DATE <= B.`end_date`) AS `TodayIsInTheRange`                                            
FROM `Items` as A                                                
LEFT JOIN `DateRanges` as B ON                                            
A.id = B.some_id
SORT BY B.`end_date` DESC

But with this query my items repeat themselves because I have two records in DateRanges for the same item.

Answer 1

try to use GROUP BY and MAX function. The first provide you only one row for each item.id, the second tell you if there is at least one date in your range

SELECT A.*, MAX(B.`start_date` <= CURRENT_DATE AND CURRENT_DATE <= B.`end_date`) AS `TodayIsInTheRange`                                            
FROM `Items` as A                                                
LEFT JOIN `DateRanges` as B ON                                            
A.id = B.some_id
GROUP BY A.id
ORDER BY B.`end_date` DESC