Please tel me which one is good approach of joining.

Question

Dear all, 
Table_2 has following data
c             na
7.000 k
3.000 j
32.000 g
Table_1 has following data
c             na
1.000 l
2.000 m
34.000 h
na is primary key for both tables.
i want only h and g should come in one row
select * from [Table_2] a CROSS JOIN table_1 b 
where a.na='g' and b.na='h'
and a.c> b.c
select * from [Table_2] a inner JOIN table_1 b 
on a.na='g' and b.na='h'
and a.c> b.c
select * from [Table_2] a , table_1 b 
where a.na='g' and b.na='h'
and a.c> b.c
please tel me which one i should follow,
as i can see  na is primary key so there can be other better methods also
please suggest.
yours sincerly

Answer 1

All ways lead to Rome, they say, but I certainly prefer the solution with CROSS JOIN.
The solution with INNER JOIN could make sense depending on the business rules, but in such case I would write it as:
SELECT *
FROM   [Table_2] a
JOIN   table_1 b ON a.c> b.c
WHERE  a.na='g'
  AND  b.na='h'
Or even:
SELECT *
FROM   (SELECT * FROM Table_2 WHERE na = 'g') AS a
JOIN   (SELECT * FROM Table_1 WHERE na = 'h') AS b ON a.c > b.c
I don't want the filtering on the individual columns in the ON clause for the JOIN. But admittedly, I rarely write queries in this style. Basically, I only do it if I do a full outer join (because else the query easily goes out of hand.)
The last version with a comma is very similar to the CROSS JOIN solution. However, while comma can be seen as a CROSS JOIN operator, it has a different precedence, which can result in unexpected compilation errors if you more JOIN operators to the query.
Erland Sommarskog, SQL Server MVP, [email protected]