What is difference between 2 sql queries? - sql

Question

I have 2 sql queries one of them work but the other gives error. Following query works well
select /*ordered*/ coupon_address.coupon,merchant_address.id
from merchant_address,
coupon_address,
customers c
WHERE merchant_address.id = coupon_address.merchant_address
and c.CUSTOMER_ID = 'temp1'
AND sdo_within_distance(c.cust_geo_location,merchant_address.store_geo_location,'distance = 1 unit=MILE') = 'TRUE';
But following query doesn't work and gives an error
select /*ordered*/ coupon_address.coupon,merchant_address.id
from coupon_address,
customers c
JOIN merchant_address ON merchant_address.id=coupon_address.merchant_address
WHERE c.CUSTOMER_ID = 'temp1'
AND sdo_within_distance (c.cust_geo_location,merchant_address.store_geo_location, 'distance = 1 unit=MILE') = 'TRUE';
Error is
ERROR at line 1: ORA-00904: "COUPON_ADDRESS"."MERCHANT_ADDRESS": invalid identifier

Answer 1

Don't ever mix explicit and implicit join syntax together! They will always lead to confusion and errors :
select /*ordered*/ coupon_address.coupon,merchant_address.id
FROM coupon_address
JOIN merchant_address
ON merchant_address.id=coupon_address.merchant_address
JOIN customers c ON c.CUSTOMER_ID = 'temp1'
WHERE sdo_within_distance (c.cust_geo_location,
merchant_address.store_geo_location,
'distance = 1 unit=MILE') = 'TRUE';
The reason it didn't work is the order that the parser evaluates the query. Probably the unknown column's table wasn't evaluated yet.

Answer 2

The JOIN has a higher precedence than the , in the FROM clause. ON is part of the JOIN so it only sees that which begin joined, including earlier joins.
So:
select /*ordered*/ coupon_address.coupon,merchant_address.id
from coupon_address,
customers c
JOIN merchant_address
ON merchant_address.id=coupon_address.merchant_address
is in essence:
select /*ordered*/ coupon_address.coupon,merchant_address.id
from coupon_address,
(customers c
JOIN merchant_address
ON merchant_address.id=coupon_address.merchant_address)
and coupon_address is not yet in scope.
As others have said, best to stick to one style of joins, either SQL-92 join keywords or the earlier commas in the from clause and join criteria in the where clause. I prefer the explicit join syntax.

Answer 3

Sagi's answer is correct. The reason your version doesn't work is because of the scoping rules around commas in the FROM clause. Oh, did I mention: Never use commas in the FROM clause. Always use explicit JOIN syntax.
Your FROM clause is evaluated as:
from coupon_address,
(customers c JOIN
merchant_address
ON merchant_address.id = coupon_address.merchant_address
)
I think this makes it obvious why you are getting the error.