Question

heres the situation. I have a table called as maps coordinates the schema is like below:

map_coordinates:
item | item_id | latitude | longitude

The idea is that this table contains a list of coordinates of different items, they could be a note, a classifieds post, an event etc. I want to be able to set it up so I have a result set as below:

item | name of item | latitude | longitude

Consider that all events, classifieds and notes are in separate tables. How could I be able to set this up as I need to show all the coordinates on a google maps along with the name of the element i.e if its a classifieds – the title of the ad, an event the title of it etc without having to make alot of sql queries.

I have the code to show it on the map – I just need to grab the details as such. Or do I have to redo my database design here?

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EDIT

Actually I have a number of tables in my database such as notes, classifieds and events etc. The point is that an item in the maps_coordinates table refers to the type of the element i.e if its a note or event and teh item_id is the actual id of that event. I don’t want to get stuck with using joins here because that would involve alot of tables. Besides I just need to grab basic information as in just the title to help in populating the map so when I hover over the individual markers I don’t have to make an ajax call just to show basic information of the element at the marker.

The other tables have their own definitions but all of them have a similar title field and it is this title field I wish to show in the same tuple as the coordinates. Or should I denormalize my tables here and have a duplicate entry for title sin the map_coordinates?

Answer 1

You can do this by creating a view that combines each of the common elements from the separate tables. In your example note, classifieds post, event, etc.

CREATE VIEW viewCommonElements
AS

SELECT 
100      as DataType,
NoteId   as ElementId,
NoteName as ElementName
FROM Notes

UNION

SELECT 
200                as DataType,
Classified_Post_Id as ElementId,
Post_Description   as ElementName
FROM Classified_Posts

UNION

SELECT 
300                as DataType,
EventId            as ElementId,
EventName          as ElementName
FROM Events

Simply add a new DataType for each table you have that you want included in your common elements. You can now set up one query that joins to the viewCommonElements view.

If a new element is created later on just modify the view and add a union select block giving it a unique datatype. You can use the DataType to distinguish the different common elements from each other.

I’ve used this method several times to harmonize dis-similar but common data.