first of all I really don't know how you gurus call this way of
writing joins:
SELECT
A.FIELD,
B.FIELD
FROM
TABLE_A A,
TABLE_B B
WHERE
A.ID_FIELD = B.ID_FIELD
I find this way very useful and readable. It works also with left and
right Joins (using *= or =* instead of = )
A friend of mine found that the inner join way (using = ) in Access is
much more slower than using the classic INNER JOIN TABLE ON FIELD
sintax. My question is: was MSSQL Server studied for using the short
way, or it is just a workaround found by someone? Is there a
performance degrade folllowing this way?
TIA,
tKtekanet (tekanet@.inwind.it) writes:
> first of all I really don't know how you gurus call this way of
> writing joins:
> SELECT
> A.FIELD,
> B.FIELD
> FROM
> TABLE_A A,
> TABLE_B B
> WHERE
> A.ID_FIELD = B.ID_FIELD
> I find this way very useful and readable.
The alternative way of writing this in so-called ANSI JOINS is:
SELECT a.field, b.field
FROM table_a a
JOIN table_b b ON a.id_field = b.id_field
These two are equvialent, both in terms of function and performance. The
optimizer will normalize both to the same internal representation.
Which one you prefer is a matter of taste. I used the method with
the join condition in the WHERE clause for many years, and I was
skeptic when I first saw the JOIN syntax. But I've changed my mind.
For a query that joins 7-8 tables and with multi-column conditions,
the JOIN syntax gives you a lot better overview, and it is also easier
to verify that you have included all conditions. The WHERE clause is
then left to proper filtering.
But, again, this is a matter of taste. Both ways of writing the JOIN is
OK by SQL Server and by ANSI.
> It works also with left and right Joins (using *= or =* instead of = )
But when it comes to outer joins, it's a whole other story. In short,
don't use *= and =*. They are deprecated, and there are all sorts of
issues with them. When it comes to outer joins, the ANSI syntax really
shines. You can do a full join, which you can't do with *=*, because
there is no such operator. You can outer join to a pair of tables which
is the result of an inner join. You can control evaluation order (which
matters for outer joins.) There is a whole lot more you can do - and
you can actuall see what you are doing. (Complex queries with *= are
far from clear-cut.)
--
Erland Sommarskog, SQL Server MVP, esquel@.sommarskog.se
Books Online for SQL Server SP3 at
http://www.microsoft.com/sql/techin.../2000/books.asp
