Question

I have a table with columns latitude and longitude. In most cases the value extends past the decimal quite a bit: -81.7770051972473 on the rare occasion the value is like this: -81.77 for some records.

How do I find duplicates and remove one of the duplicates for only the records that extend beyond two decimal places?

Answer 1

Using some creative substring, float, and charindex logic, I came up with this:

delete l1
from 
    latlong l1
    inner join (
        select
            id,
            substring(cast(latitude as varchar), 0, INSTR(CAST(latitude as varchar))+3, '.') as truncatedLat
        from
            latlong
    ) l2 on
        l1.id <> l2.id
        and l1.latitude = cast(l2.truncatedLat as float)

Before running, try select * in lieu of delete l1 first to make sure you’re deleting the right rows.

I should note that this worked on SQL Server using functions I know exist in MySQL, but I wasn’t able to test it against a MySQL instance, so there may be some little tweaking that needs to be done. For example, in SQL Server, I used charindex instead of instr, but both should work similarly.