Question

I am trying to find out what’s the most optimized SQL Query to achieve the following.

I have a table containing ZipCodes/PostalCodes, let’s assume the following structure:

table_codes:

ID   |  ZipCode
---------------
1       1234
2       1235
3       456

and so on.

The users of my application fill up a profile where they are required to enter their ZipCode (PostalCode).
Assuming that sometimes, the user will enter a ZipCode not defined in my table, I am trying to suggest a Best Match based on the zip entered by the user.

I am using the following query:

Declare @entered_zipcode varchar(10)
set @entered_zipcode = '23456'


SELECT TOP 1 table_codes.ZipCode
FROM    table_codes
where   @entered_zipcode  LIKE table_codes.ZipCode + '%'
or table_codes.ZipCode + '%' like @entered_zipcode  + '%'
ORDER BY table_codes.ZipCode, LEN(table_codes.ZipCode) DESC

Basically, I am trying the following:

• if the @entered_zipcode is longer than any zip code in the table, I am trying to get to get the best prefix in the zip table matching the @entered_zipcode

• if the @entered_zipcode is shorter than any existing code in the table, I am trying to use it as a prefix and get the best match in the table

Moreover, I am building a temp table with the following structure:

#tmpTable
------------------------------------------------------------------------------------
ID | user1_enteredzip | user1_bestmatchzip | user2_enteredzip | user2_bestmatchzip |
------------------------------------------------------------------------------------
1  |   12             |     *1234*         |       4567       |       **456**      |
2  |
3  |
4  |

Entered zip is the one the user enters and the code between * .. * is the best matching code from my lookup table, that I am trying to get using the query below.

The query seems to take a little bit to long and this is why I am asking for help in optimizing it:

        update  #tmpTable
        set     user1_bestmatchzip = ( SELECT TOP 1
                                            zipcode
                                    FROM    table_codes
                                    where   #tmpTable.user1_enteredzip  LIKE table_codes.zipcode + '%'
                                            or table_codes.zipcode + '%' like #tmpTable.user1_enteredzip + '%'
                                    ORDER BY table_codes.zipcode, LEN(table_codes.zipcode) DESC
                                  ),
                user2_bestmatchzip = ( SELECT TOP 1
                                            zipcode
                                    FROM    table_codes
                                    where   #tmpTable.user2_enteredzip  LIKE table_codes.zipcode + '%'
                                            or table_codes.zipcode + '%' like #tmpTable.user2_enteredzip + '%'
                                    ORDER BY table_codes.zipcode, LEN(table_codes.zipcode) DESC
                                  )
         from #tmpTable

Answer 1

What if you change your temp table to be like:

id  |  user | enteredzip | bestmatchzip 
10  |  1    | 12345      | 12345
20  |  2    | 12         | 12345

That is: use a column to save the user number (1 or 2). This way you will update one row at a time.

Also, the ORDER BY takes time, did you set indices on the zipcode? Couldn’t you create a field “length” in the zipcodes table to pre-compute the zipcodes lenghts?

EDIT:
I was thinking that ordering by LEN makes no sense, you could remove that! If the zipcodes cannot have duplicates, then ordering by the zipcode is just enought. If they can though, the LEN will always be equal!