Question

First Query:

Select * from table1 inner join table2 on table1.Id = table2.Id

Second Query:

Select * from table1, table2 where table1.Id = table2.Id

What is difference between these query regarding performance which should one use?

Answer 1

The two statements you posted are logically identical. There isn’t really a
practical reason to prefer one over the other, it’s largely a matter of
personal style and readability. Some people prefer the INNER JOIN syntax and
some prefer just to use WHERE.

Refering to Using Inner Joins:

In the ISO standard, inner joins can
be specified in either the FROM or
WHERE clause. This is the only type of
join that ISO supports in the WHERE
clause. Inner joins specified in the
WHERE clause are known as old-style
inner joins.

Refering to Join Fundamentals:

Specifying the join conditions in the
FROM clause helps separate them from
any other search conditions that may
be specified in a WHERE clause, and is
the recommended method for specifying
joins.

Personaly, I prefer using INNER JOIN. I find it much clearer, as I can separate the join conditions from the filter conditions and using a seperate join block for each joined table.