I have a table "Price" that should be filtered according to a value stored in an another table "CutPrice" (meaning only prices inferior to the parameter stored should be displayed).
I experimented various way, and for a laugh I did the following:
SELECT Location, Price, CutoffPrice
FROM LocPrice INNER JOIN
CutPrice ON CutPrice.CutOffPrice < LocPrice.Price
Using the inferior than sign works perfectly, it's even faster than the Case statement I used in another version of the query.
I try googling for it, to see if it's standard, recommended, not recommended, even a bug , perhaps ?
I could not find anything. So I know, the question might be a bit broad for the site, but is this a standard use of JOINS or is there anything to be careful about when using this ? Particularly about T-SQL on SQL server 2005
Non-equi joins are a pretty standard part of SQL. See http://blog.mclaughlinsoftware.com/oracle-sql-programming/basic-sql-join-semantics/ for example. Most of the major databases support non-equi joins, usually with both SQL 92 JOIN ON syntax and pre-SQL 92 WHERE syntax. However, if you have a particular database in mind searching for 'non-equi join <db name>' will usually find mention of it doesn't support them, e.g. Hive: work around for non equi left join
Related
This question already has answers here:
Oracle Joins - Comparison between conventional syntax VS ANSI Syntax
(11 answers)
Closed 9 years ago.
I have come across many websites to find the answer about which one is better, ANSI or non- ANSI syntax. What is the difference between these two queries?
select a.name,a.empno,b.loc
from tab a, tab b
where a.deptno=b.deptno(+);
and:
select a.name,a.empno,b.loc
from tab a
left outer join tab b on a.deptno=b.deptno;
The result is same in both the cases. The second query is also longer. Which one is better?
suppose if we have added another table Salgrade in the above query based on what conditions we need to join them?? ..
can any one assume one table and give me explanation
both syntaxes usually work without problems, but if you try to add a where condition you will see that with the second one is much simpler to understand which is the join condition and which is the where clause.
1)
SELECT a.name,
a.empno,
b.loc
FROM tab a,
tab b
WHERE a.deptno = b.deptno(+)
AND a.empno = 190;
2)
SELECT a.name,
a.empno,
b.loc
FROM tab a,
LEFT OUTER JOIN tab b
ON a.deptno = b.deptno
WHERE a.empno = 190;
Also, it's much easier to recognize an outer join and do not forget to include the (+). Overall you can say it's just a question of taste, but the truth is that the second syntax is much more readable and less prone to errors.
The first is a legacy Oracle specific way of writing joins, the second is ANSI SQL-92+ standard and is the preferred one.
Extensively discussed many a times, including one by me.
Use explicit JOINs rather than implicit (regardless whether they are outer joins or not) is that it's much easier to accidently create a cartesian product with the implicit joins.
With explicit JOINs you cannot "by accident" create one. The more tables are involved the higher the risk is that you miss one join condition.
Basically (+) is severely limited compared to ANSI joins. Furthermore it is only available in Oracle whereas the ANSI join syntax is supported by all major DBMS
SQL will not start to perform better after migration to ANSI syntax - it's just different syntax.
Oracle strongly recommends that you use the more flexible FROM clause join syntax shown in the former example. In the past there were some bugs with ANSI syntax but if you go with latest 11.2 or 12.1 that should be fixed already.
Using the JOIN operators ensure your SQL code is ANSI compliant, and thus would allow a front-end application to be more easily ported for other database platforms.
Join conditions have a very low selectivity on each table and a high selectivity on the tuples in the theoretical cross product. Conditions in the where statement usually have a much higher selectivity.
Oracle internally converts ANSI syntax to the (+) syntax, you can see this happening in the execution plan's Predicate Information section.
If you are using 11.2 I advise ANSI join. If you use 12C, there are some new bugs unearthed on OUTER JOINS.
I also remember some bugs in Oracle while using ANSI syntax, before 11.2 where it got fixed in 11.2.
In my opinion, I am not a big fan of ANSI syntax, though Oracle does confirm to the standards of ANSI, it is not totally bug free.
please, read this article about joins.
result of your example is not same, if you have data in B table and not in A table
Is there any support for natural joins in recent Microsoft SQL Server editions? Or is there a good alternative for making SQL Server work out the predicates that would have been in the ON clauses based on the referential integrity?
No, and thank the lucky stars
I can't believe that you'd want the engine to guess the JOIN for you
Related links:
SQL Server - lack of NATURAL JOIN / x JOIN y USING(field)
is NATURAL JOIN any better than SELECT FROM WHERE in terms of performance ?
Edit, to explain why
The JOIN (whether USING or ON) is clear and explicit
I should be able to name my columns for the entity stored in the table, without worrying about what a column is called in another table, without NATURAL JOIN side effects
Quoting Bill Karwin in this excellent answer:
I never use NATURAL JOIN because I don't like the possibility that the
join could do something I don't intend just because some column name
exists in both tables.
MS SQL does not support natural join, neither join using (). You have to explicitly write down all your attributes used in the join.
If the datamodel changes, you have to change all "natural join" written by hand and make sure your join condition is ok again.
I wouldn't expect to see it any time soon. A Connect suggestion from 2006 has very little info other than:
Thanks for your feedback. We will look into your request for one of the upcoming releases.
And has only received ~30 upvotes
use Full Outer join instead of Natural Join. It works for me.
This question already has answers here:
Closed 12 years ago.
Possible Duplicate:
Is there something wrong with joins that don't use the JOIN keyword in SQL or MySQL?
Hi,
i'ave always retrieved data without joins...
but is there a benefit to one method over the other?
select * from a INNER JOIN b on a.a = b.b;
select a.*,b.* from a,b where a.a = b.b;
Thanks!
The first method using the INNER JOIN keyword is:
ANSI SQL standard
much cleaner and more expressive
Therefore, I always cringe when I see the second option used - it just bloats up your WHERE clause, and you can't really see at one glance how the tables are joined (on what fields).
Should you happen to forget one of the JOIN conditions in a long list of WHERE clause expressions, you suddenly get a messy cartesian product..... can't do that with the INNER JOIN keyword (you must express what field(s) to join on).
I'd say the biggest benefit is readability. The version with the explicitly named join types are much easier for me to comprehend.
You are using a different syntax for a JOIN, basically. As a matter of best practices, it is best to use the first syntax (explicit JOIN) because it is clearer what the intention of the query is and makes the code easier to maintain.
These are both joins. they are just two different syntactical representations for joins. The first one, (using the "Join" keyword, is the current ANSI Standard (as of 1992 I think).
In the case of inner joins only, the two differeent representations are functionally identical, but the latter ANSI SQL92 standard syntax is much moire readable, once you get used to it, because each individual join condition is associated with the pair of intermediate resultsets being joined together, In the older representation, the join conditions are all together, along with the overall queries' filter conditions, in the where clause, and it is not as clear which is which. This makes identifying bad join conditions (where for example, an unintended cartesian product will be generated) much more difficult.
But more important, perhaps, is that, when performing an outer Join, in certain scenarios, the older syntax is NOT equivilent, and in fact will generate the WRONG resultset.
You should transition to the newer syntax for all your queries.
You've always retrieved the data with joins. The second query is using old syntax, but in the background it is still join :)
This depends on the RDBMS but in the case of SQL server I understand that the utilizing the former syntax allows for better optimization. This is less of a SQL question and more of a vendor specific question.
You can also use the EXPLAIN (SQL Server: Query Execution Plan) type functions to help you understand if there is a difference. Each query is unique and I imagine that the stored statistics can (and will) alter the behavior.
First option:
SELECT Table1.* ,Table2.Price AS Price
FROM
Table1,Table2
WHERE
Table1.ID = Table2.ID
Second option:
SELECT Table1.* ,Table2.Price AS Price
FROM
Table1 INNER JOIN Table2 ON Table1.ID = Table2.ID
Which one is better and most efficient?
It may give you the same results, however the second option is better because it follows the latest standards, and properly defines what is the join and what may be a where clause. In terms of performance the two statements as above should perform the same.
The second way does the same thing, only with ANSI (American National Standards Institute standardized Structured Query Language) SQL, a standard form of SQL. Research it further to find its pros and cons.
http://it.toolbox.com/blogs/oracle-experience/a-case-for-ansi-sql-15647
They're both joins, the first is just using the implicit syntax and the second is using the explicit syntax.
Tons of duplicate questions
Also, it should be covered in any decent SQL book (I've got my understanding of the question from the O'Reilly pocket reference). Also, I still wonder where people get the old syntax examples, maybe I just learned SQL from the good sources. Also, while people repeat that both variants produce the same query with the same performance, I still prefer to doubt that when the talk is not about some DBMS specifically stating that in its documentation and especially when the talk is about DBMS in general.
the first query join style uses ancient join syntax, while the second style is more current. In most cases they result in the exact same query execution plan. However when using LEFT AND RIGHT OUTER JOINS, you can have probelms, see this answer and the comments:
ANSI joins versus "where clause" joins
from SQL Server BOL(2000) "In earlier
versions of Microsoft® SQL Server™
2000 left and right outer join
conditions were specified in the WHERE
clause using the *= and =*
operators. In some cases, this syntax
results in an ambiguous query that can
be interpreted in more than one way.
EDIT 9-3-10: I found this blog entry recently that was very enlightening. http://optimizermagic.blogspot.com/2007/12/outerjoins-in-oracle.html
There are times when one or the other join syntax may in fact perform better. I have also found times when a have noticed a slight performance increase (only noticeable in VLDBs) when choosing the Oracle join syntax over the ANSI one. Probably not enough to get fussy over, but for those serious about mastering the Oracle DB, it may be helpful to review the article.
I am aware of two outer join syntaxes for Oracle:
select a, b
from table1
left outer join table2
on table2.foo = table1.foo
OR
select a, b
from table1, table2
where table2.foo(+) = table1.foo
(assuming I got the syntax of the second sample right.)
Is there a performance difference between these? At first I thought it must just be a style preference on the part of the developer, but then I read something that made me think maybe there would be a reason to use one style instead of the other.
"maybe there would be a reason to use
one style instead of the other. "
There are reasons, but not performance related ones. The ANSI style outer joins, as well as being standard, offer FULL OUTER JOINs and outer joins to multiple tables.
Oracle didn't support ANSI syntax prior to version 9i.
Since that version, these queries do the same and yield the same plan.
Correct pre-9i syntax is this:
SELECT a, b
FROM table1, table2
WHERE table2.foo(+) = table1.foo
There is no performance difference. You can also check the execution plans of both queries to compare.
Theoretically, the second query performs the Cartesian product of the two tables and then selects those meeting the join condition. In practice, though, the database engine will optimize it exactly the same as the first.
I found some additional information in answer to my own question. Looks like the old style is very limiting, as of this doc from 3 years ago.
http://www.freelists.org/post/oracle-l/should-one-use-ANSI-join-syntax-when-writing-an-Oracle-application,2
I think perhaps it would only make sense to use the old style if for some reason the queries might be run on an outdated version of Oracle.
The stuff I see at work is almost all in the old style, but it's probably just because the consultants have been working in Oracle since before 9i and they likely didn't see a reason to go update all the old stuff.
Thanks all!
It's not the same. In the first case you're forcing to join the tables in that order.
In the second case Oracle Planner can choose the best option to execute the query.
In this trivial case the result probably will be the same in all the executions, but if you use that syntax in more complex cases the difference will be shown.