mysql inner join count issue

Question

I have two tables: Table1 and Table2.

Table1:

log_id | postcode
1      |  LS11LS

Table2:

region | postcode
Leeds     | LS1
Leeds     | LS11

When I use the following query,

SELECT table2.region 'Region', 
       Count(table1.postcode) AS 'count' 
FROM   table1 
INNER JOIN table2 
   ON table1.postcode LIKE Concat(table2.postcode, '%') 

I get

Region   |   count
Leeds    |    2

where it should be 1 because there is only one record on Table1. Any solution for this ?

Answer 1

Sounds like you need to use DISTINCT :

SELECT table2.region 'Region', 
    COUNT( DISTINCT table1.log_id )  as 'count' 
FROM table1 
    INNER JOIN table2 ON 
        table1.postcode LIKE CONCAT( table2.postcode,  '%' )

I replaced postcode with log_id as it perhaps is your unique column.

EDIT: While I'm not exactly sure what you're looking for, here's an alternative approach using a subquery:

SELECT Region, COUNT(1) as 'Count'
FROM Table1 T
    JOIN (
        SELECT DISTINCT T2.Region, T.PostCode
        FROM table1 T
            INNER JOIN table2 T2 ON 
                    T.postcode LIKE CONCAT( T2.postcode,  '%' )
    ) T2 ON T.PostCode = T2.PostCode

Answer 2

ok the final solution for this thing after 8 hours . by the end user post code entry , trim the post code off any spaces , and then str_replace the spaces to nothing , and then take off the last 3 letter / numbers of the string . and save it as an additional column along with the original postcode , now you will have post codes store like LS1 . LS11 , and instead of inner join using like , use = . this is i believe the only way out there.

see This link for more info