Join Clause With a XOR Statement - sql

Question

I am doing a join and I can't seem to make this XOR to properly work.
SELECT t1.COMPANY, t1.MILES,
CASE WHEN t2.MILES IS NULL THEN t3.MILES
ELSE t2.MILES
END AS MILES2,
CASE WHEN t2.MILES = t1.MILES AND t2.MILES != 9999 THEN t2.FLATRATE
ELSE t3.RATEBASIS
END AS RATE
FROM TABLE1 AS t1
LEFT JOIN TABLE2 AS t2
ON t1.[COMPANY] = t2.[COMPANYCODE] AND (t1.[MILES] = t2.[MILES])
INNER JOIN (
SELECT TOP 1 TRUCKERCODE, MILES, RATEBASIS, FLATRATE FROM TABLE2 WHERE MILES = 9999
) AS t3
ON t1.[COMPANY] = t3.[COMPANYCODE]
I need the ON clause to join if the miles are the same then get the given fields that match otherwise the default data I need to get out of the second table is where the miles is equal to 9999. Right now with that ON clause I get many extra rows where the MILES equals lets say 45, it gets the data from TABLE2 where miles equals 45 and all the data where miles equals 9999. I need it to do one or the other but not both. This is what my tables would look like
TABLE1 TABLE2
ID COMPANY MILES ETC ID COMPANYCODE MILES RATE
1 ILLINI 50 1 ILLINI 50 3.2
2 ILLINI 110 2 ILLINI 110 5.2
3 ILLINI 150 3 ILLINI 150 2.4
4 ILLINI 200 4 ILLINI 200 1.9
5 ILLINI 250 5 ILLINI 9999 1.5
6 ILLINI 300
7 ILLINI 350
8 ILLINI 400
9 ILLINI 450
10 ILLINI 500
Desired Output
COMPANY MILES MILES2 RATE
ILLINI 50 50 3.2
ILLINI 110 110 5.2
ILLINI 150 150 2.4
ILLINI 200 200 1.9
ILLINI 250 9999 1.5
ILLINI 300 9999 1.5
ILLINI 350 9999 1.5
ILLINI 400 9999 1.5
ILLINI 450 9999 1.5
ILLINI 500 9999 1.5

Answer 1

I think this will give you what you want:
SELECT t1.COMPANY, t1.MILES,
CASE WHEN t2.MILES IS NULL THEN t3.MILES
ELSE t2.MILES
END AS MILES2,
CASE WHEN t2.MILES IS NULL THEN t3.RATE
ELSE t2.RATE
END AS RATE
FROM TABLE1 AS t1
LEFT JOIN TABLE2 AS t2
ON t1.[COMPANY] = t2.[COMPANYCODE] AND (t1.[MILES] = t2.[MILES])
INNER JOIN (
SELECT TOP 1 COMPANYCODE, MILES, RATE FROM TABLE2 WHERE MILES = 9999
) AS t3
ON t1.[COMPANY] = t3.[COMPANYCODE]
If there is a match in MILES, then output contains both records from TABLE1, TABLE2. Otherwise, output contains record from left table, i.e. TABLE1 and the specific record from TABLE2 with MILES = 9999.
Please note that TOP 1 is used in the last sub-query just in case more than one records with MILES = 9999 exist in TABLE2.
Output:
COMPANY MILES MILES2 RATE
----------------------------
ILLINI 50 50 3,2
ILLINI 110 110 5,2
ILLINI 150 150 2,4
ILLINI 200 200 1,9
ILLINI 250 9999 1,5
ILLINI 300 9999 1,5
ILLINI 350 9999 1,5
ILLINI 400 9999 1,5
ILLINI 450 9999 1,5
ILLINI 500 9999 1,5
SQL Fiddle Demo here

Answer 2

I would do based on a double left-join.. once for a match, and if not, then default to the 9999 instance
SELECT
T1.*,
coalesce( T2.miles, T3.miles ) as Miles2,
coalesce( T2.rate, T3.rate ) as MileageRate
FROM
TABLE1 T1
LEFT JOIN TABLE2 T2
on T1.Company = T2.CompanyCode
AND T1.Miles = T2.Miles
LEFT JOIN TABLE2 T3
on T1.Company = T3.CompanyCode
AND T3.Miles = 9999
Confirmed working at this SQL Fiddle link