iphone - SQL Query for Performing Radius Search based on Latitude Longitude

Question

We have a restaurant table that has lat-long data for each row.

We need to write a query that performs a search to find all restaurants within the provided radius e.g. 1 mile, 5 miles etc.

We have the following query for this purpose:

***Parameters***

Longitude: -74.008680
Latitude: 40.711676
Radius: 1 mile

***Query***

SELECT *
FROM restaurant
WHERE (
POW( ( 69.1 * ( Longitude - -74.008680 ) * cos( 40.711676 / 57.3 ) ) , 2 ) + POW( ( 69.1 * ( Latitude - 40.711676 ) ) , 2 )
) < ( 1 *1 );

The table has about 23k rows. The size of the result set is weird at times e.g. for a 5.4 mile search, it gives back 880 rows and for 5.5 miles, it gives back 21k rows.

This table contains restaurant data for nyc - so the real distribution is not as per the result set.

Question: IS THERE ANYTHING WRONG With this query?

DB: MySQL, Longitude: DECIMAL(10,6), Latitude: DECIMAL(10,6)

Answer 1

IS THERE ANYTHING WRONG With this query?

In my opinion the WHERE clause is going to be slow because of the maths involved, and the use of functions in the WHERE clause will prevent the database using an index to speed the query - so, in effect, you will examine every restaurant in the database, and perform the great-circle maths on every row, every time you make a query.

Personally I would calculate the TopLeft and BottomRight co-ordinates of a square (which only needs to be crudly calculated using pythagoras) with sides equal to the range you are looking for, and then perform the more complicated WHERE clause test on the smaller subset of records that are within that Lat/Long square.

With an Index on Lat & Long in the database the query

WHERE     MyLat >= @MinLat AND MyLat <= @MaxLat
      AND MyLong >= @MinLong AND MyLong <= @MaxLong

should be very efficient

(Please note that I have no knowledge of MySQL specifically, only of MS SQL)