fetch data from and to date to get all matching results - postgresql

Question

Hello everyone I have to get data from and to date, I tried using between clause which fails to retrieve data what I need. Here is what I need.
I have table called hall_info which has following structure
hall_info
id | hall_name |address |contact_no
1 | abc | India |XXXX-XXXX-XX
2 | xyz | India |XXXX-XXXX-XX
Now I have one more table which is events, that contains data about when and which hall is booked on what date, the structure is as follows.
id |hall_info_id |event_date(booked_date)| event_name
1 | 2 | 2015-10-25 | Marriage
2 | 1 | 2015-10-28 | Marriage
3 | 2 | 2015-10-26 | Marriage
So what I need now is I wanna show hall_names that are not booked on selected dates, suppose if user chooses from 2015-10-23 to 2015-10-30 so I wanna list all halls that are not booked on selected dates. In above case both the halls of hall_info_id 1 and 2 ids booked in given range but still I wanna show them because they are free on 23,24,27 and on 29 date.
In second case suppose if user chooses date from 2015-10-25 and 2015-10-26 then only hall_info_id 2 is booked on both the dates 25 and 26 so in this case i wanna show only hall_info_id 1 as hall_info_id 2 is booked.
I tried using inner query and between clause but I am not getting required result to simply i have given only selected fields I have more tables to join so i cant paste my query please help with this. Thanks in advance for all who are trying.

Answer 1

Some changes in Yasen Zhelev's code:
SELECT * FROM hall_info
WHERE id not IN (
SELECT hall_info_id FROM events
WHERE event_date >= '2015-10-23' AND event_date <= '2015-10-30'
GROUP BY hall_info_id
HAVING COUNT(DISTINCT event_date) > DATE_PART('day', '2015-10-30'::timestamp - '2015-10-23'::timestamp))

Answer 2

I have not tried it but how about checking if the number of bookings per hall is less than the actual days in the selected period.
SELECT * FROM hall_info WHERE id NOT IN
(SELECT hall_info_id FROM events
WHERE event_date >= '2015-10-23' AND event_date <= '2015-10-30'
GROUP BY hall_info_id
HAVING COUNT(id) < DATEDIFF(day, '2015-10-30', '2015-10-23')
);
That will only work if you have one booking per day per hall.

Answer 3

To get the "available dates" for the hall returned, your query needs a row source of all possible dates. For example, if you had a calendar table populated with possible date values, e.g.
CREATE TABLE cal (dt DATE NOT NULL PRIMARY KEY) Engine=InnoDB
;
INSERT INTO cal (dt) VALUES ('2015-10-23')
,('2015-10-24'),('2015-10-25'),('2015-10-26'),('2015-10-27')
,('2015-10-28'),('2015-10-29'),('2015-10-30'),('2015-10-31')
;
The you could use a query that performs a cross join between the calendar table and hall_info... to get every hall on every date... and an anti-join pattern to eliminate rows that are already booked.
The anti-join pattern is an outer join with a restriction in the WHERE clause to eliminate matching rows.
For example:
SELECT cal.dt, h.id, h.hall_name, h.address
FROM cal cal
CROSS
JOIN hall_info h
LEFT
JOIN events e
ON e.hall_id = h.id
AND e.event_date = cal.dt
WHERE e.id IS NULL
AND cal.dt >= '2015-10-23'
AND cal.dt <= '2015-10-30'
The cross join between cal and hall_info gets all halls for all dates (restricted in the WHERE clause to a specified range of dates.)
The outer join to events find matching rows in the events table (matching on hall_id and event_date. The trick is the predicate (condition) in the WHERE clause e.id IS NULL. That throws out any rows that had a match, leaving only rows that don't have a match.
This type of problem is similar to other "sparse data" problems. e.g. How do you return a zero total for sales by a given store on a given date, when there are no rows with that store and date...
In your case, the query needs a source of rows with available date values. That doesn't necessarily have to be a table named calendar. (Other databases give us the ability to dynamically generate a row source; someday, MySQL may have similar features.)
If you want the row source to be dynamic in MySQL, then one approach would be to create a temporary table, and populate it with the dates, run the query referencing the temporary table, and then dropping the temporary table.
Another approach is to use an inline view to return the rows...
SELECT cal.dt, h.id, h.hall_name, h.address
FROM (
SELECT '2015-10-23'+INTERVAL 0 DAY AS dt
UNION ALL SELECT '2015-10-24'
UNION ALL SELECT '2015-10-25'
UNION ALL SELECT '2015-10-26'
UNION ALL SELECT '2015-10-27'
UNION ALL SELECT '2015-10-28'
UNION ALL SELECT '2015-10-29'
UNION ALL SELECT '2015-10-30'
) cal
CROSS
JOIN hall_info h
LEFT
JOIN events e
ON e.hall_id = h.id
AND e.event_date = c.dt
WHERE e.id IS NULL
FOLLOWUP: When this question was originally posted, it was tagged with mysql. The SQL in the examples above is for MySQL.
In terms of writing a query to return the specified results, the general issue is still the same in PostgreSQL. The general problem is "sparse data".
The SQL query needs a row source for the "missing" date values, but the specification doesn't provide any source for those date values.
The answer above discusses several possible row sources in MySQL: 1) a table, 2) a temporary table, 3) an inline view.
The answer also mentions that some databases (not MySQL) provide other mechanisms that can be used as a row source.
For example, PostgreSQL provides a nifty generate_series function (Reference: http://www.postgresql.org/docs/9.1/static/functions-srf.html.
It should be possible to use the generate_series function as a row source, to supply a set of rows containing the date values needed by the query to produced the specified result.
This answer demonstrates the approach to solving the "sparse data" problem.
If the specification is to return just the list of halls, and not the dates they are available, the queries above can be easily modified to remove the date expression from the SELECT list, and add a GROUP BY clause to collapse the rows into a distinct list of halls.