Using RODBC package in R and sqlQuery function to join 3 tables from a Database

Question

can you help me to understand how i can create a left join between a master table x1 and two other tables x2 and x3 using the sqlQuery function from the RODBC package in R.

After I setup the database connection I successfully can join two tables:

library RODBC

dataframe <-sqlQuery(conn,"
SELECT
sum(A1.revenue1),
sum(A1.revenue2), 
sum(A1.revenue3),
A2.SERVICE_TYPE_NAME
FROM
(FINANCE.x1 A1 LEFT JOIN CORE.x2 A2
ON (A1.YEAR_NUM = A2.YEAR_NUM 
AND A1.SERVICE_TYPE_KEY = A2.SERVICE_TYPE_KEY)
)
WHERE A1.YEAR_NUM = '2015' 
AND A2.SERVICE_TYPE_KEY='2'
GROUP BY A2.SERVICE_TYPE_NAME
")

but I fail when I try to bring a 3rd to the equation trying this:

dataframe <-sqlQuery(conn,"
SELECT
sum(A1.revenue1),
sum(A1.revenue2), 
sum(A1.revenue3),
A2.SERVICE_TYPE_NAME
FROM
(FINANCE.x1 A1 LEFT JOIN CORE.x2 A2
ON (A1.YEAR_NUM = A2.YEAR_NUM 
AND A1.SERVICE_TYPE_KEY = A2.SERVICE_TYPE_KEY)

FINANCE.x1 A1 LEFT JOIN BRAND.x3
ON (A1.brand_ID=A3.brand_ID))
WHERE A1.YEAR_NUM = '2015' 
AND A2.SERVICE_TYPE_KEY='2'
GROUP BY A2.SERVICE_TYPE_NAME
")

Answer 1

Your second SQL needs to be cleaned up. You only mention each table once when doing a join. Try this:

SELECT SUM(A1.revenue1),
       SUM(A1.revenue2), 
       SUM(A1.revenue3),
       A2.SERVICE_TYPE_NAME
FROM FINANCE.x1 A1
LEFT JOIN CORE.x2 A2
    ON A1.YEAR_NUM = A2.YEAR_NUM AND
       A1.SERVICE_TYPE_KEY = A2.SERVICE_TYPE_KEY
LEFT JOIN BRAND.x3
    ON A1.brand_ID=A3.brand_ID
WHERE A1.YEAR_NUM = '2015' AND
      A2.SERVICE_TYPE_KEY = '2'
GROUP BY A2.SERVICE_TYPE_NAME