As the title suggests, does an equal to the lateral join exist in redshift? I haven't run into a situation where it might be necessary yet, but it seems hard to imagine replicating the functionality of a lateral join if I needed to with what I know now.
Related
I have to write on paper a good physical plan for a Postgresql's query with several natural join, is it the same as treating a query with a simple join or should I use a different approach?
I am working on this one, by the way
SELECT zname
FROM Cage natural join Animal natural join DailyFeeds natural join Zookeeper
WHERE shift=’const’ AND clocation=’const’;
By Oracle
A NATURAL JOIN is a JOIN operation that creates an implicit join
clause for you based on the common columns in the two tables being
joined. Common columns are columns that have the same name in both
tables.
I think the above is answering following
is it the same as treating a query with a simple join or should I use a different approach?
I hope it helps.
Why is it that in PostgreSQL you cannot use:
FULL OUTER JOIN
. . .
ON POSITION(table1.column1 IN table2.column1) <> 0,
But you can accomplish the same thing with a left join and a right join and then using a union all to join the results. It's the same exact result set that I want and I feel it should be possible since it's possible to just do the right and left join manually. I can live with having to do it, but it'd be a lot simpler to write with just using a Full Outer Join.
I want to join two tables together and add additional information from two other tables to the same columns in both queried tables. I've come up with the below code, which works, but I don't feel comfortable about having to add another JOIN clause for each table, as it would make the query substantially long if I wanted to join/add more things.
Is there a way to combine it, so that I can join additional tables only once (just use S and E aliases every time)?
SELECT
J.JobId,
J.StandardJobId,
S.JobName,
J.EngineerId,
E.EngineerName,
JF.JobId AS FollowUpJobId,
JF.StandardJobId AS FollowUpStandardJobId,
SF.JobName AS FollowUpJobName,
JF.EngineerId AS FollowUpEngineerId,
EF.EngineerName AS FollowUpEngineerName
FROM
Jobs J
INNER JOIN
Jobs JF
ON
J.FollowUpJobId = JF.JobId
INNER JOIN
StandardJobs S
ON
J.StandardJobId = S.StandardJobId
INNER JOIN
Engineers E
ON
E.EngineerId = J.EngineerId
INNER JOIN
StandardJobs SF
ON
SF.StandardJobId = JF.StandardJobId
INNER JOIN
Engineers EF
ON
EF.EngineerId = JF.EngineerId
One approach would be to use a Common Table Expression (CTE) - something like:
with cte as
(SELECT J.JobId,
J.StandardJobId,
S.JobName,
J.EngineerId,
E.EngineerName,
J.FollowUpJobId
FROM Jobs J
INNER JOIN StandardJobs S ON J.StandardJobId = S.StandardJobId
INNER JOIN Engineers E ON E.EngineerId = J.EngineerId)
SELECT O.*,
F.StandardJobId AS FollowUpStandardJobId,
F.JobName AS FollowUpJobName,
F.EngineerId AS FollowUpEngineerId,
F.EngineerName AS FollowUpEngineerName
FROM CTE AS O
JOIN CTE AS F ON O.FollowUpJobId = F.JobId
You can sort of do this with either a CTE (Common Table Expressions, the WITH clause) or a View:
;WITH Jobs_Extended As
(
SELECT j.*,
s.JobName,
E.EngineerName
FROM Jobs As j
JOIN StandardJobs As s ON s.StandardJobId = j.StandardJobId
JOIN Engineer As e ON e.EngineerId = j.EngineerId
)
SELECT
J.JobId,
J.StandardJobId,
J.JobName,
J.EngineerId,
J.EngineerName,
JF.JobId AS FollowUpJobId,
JF.StandardJobId AS FollowUpStandardJobId,
JF.JobName AS FollowUpJobName,
JF.EngineerId AS FollowUpEngineerId,
JF.EngineerName AS FollowUpEngineerName
FROM Jobs_Extended J
JOIN Jobs_Extended JF ON J.FollowUpJobId = JF.JobId
In this example the CTE Jobs_Extended becomes a defined alias for the relationship between the Jobs, Engineers and StandardJobs tables. Then once defined, you can use it multiple times in the query without having to redefine those interior relations.
You can do the same thing by change the WITH to a View, which will make the defined alias permannet in your database.
No, you cannot avoid JOINing related tables each time a separate reference is needed. The issue is that you are not working with the tables in a general sense but instead working with the specific rows of each table, even more specifically, just those rows that match the JOIN and WHERE conditions.
There is no way to specify the references to either StandardJobs or Engineers only once because you are needing to work with two rows from each table at the same time, at least in the given example.
However, depending on which direction you are wanting to go with "additional tables" (more references to Jobs or more lookups like StandardJobs and Engineers for the given 2 references of Jobs), the CTE construct shown by Mark is the probably the easiest / best way to abstract it. I posted this answer mainly to explain the issue at hand.
these are 3 approaches how to make a join. I would like to hear some word on perforance of these 3 queries.
Thank you
SELECT * FROM
tableA A LEFT JOIN tableB B
INNER JOIN tableC C
ON C.ColumnC = B.ColumnB
ON B.ColumnB = A.ColumnB
WHERE ColumnX = 'XY'
Versus
SELECT * FROM
tableA A LEFT JOIN tableB B
ON B.ColumnB = A.ColumnB
INNER JOIN tableC C
ON C.ColumnC = B.ColumnB
WHERE ColumnX = 'XY'
Versus Common Table Expression
WITH T...
It does not matter.
SQL Server has a cost-based optimizer (as opposed to a rule-based optimizer). That means that the engine is able to figure out that both of your first two options are identical. Run your estimated and actual execution plans and you will see that this is the case.
The only reason you would choose one option over the other is for readability's sake. I go with your second option, because it's a lot easier to read when there are a great many joins involved. ON clauses in reverse order become quite difficult to track.
In my experience, any of the above could be quicker depending on your tables.
As you're setting up joins, you want to start with the most restrictive as possible (without negatively affecting your end result, obviously). This same logic also applies to the Where clause for the same reason. By starting with the most restrictive, you're limiting the number of rows that are being joined and thus evaluated by the Where clause and then returned/manipulated in the select clause. For my answers below regarding the three specific scenarios, I'm assuming a sufficiently complicated query that is doing more than just looking to combine data from multiple tables (i.e., queries answering specific questions).
If Table A is huge and Tables B & C are smaller and more directly related to the data you're trying to isolate, then the first option would likely be fastest.
If Table B or C are huge and Table A is more related to your desired data, the second option would likely be fastest.
As far as option 3 goes, I love CTEs but I try to only use them when I need to do so. Using a CTE will speed up your overall query if the data joined, manipulated, and returned by the CTE is only related to the rest of the query in a limited fashion. Including tables that are only partially related to your end result in your primary string of joins is going to needlessly slow down your query. If you can parse out that data into a CTE, it can run quickly by itself and then be incorporated back into the main query at the end.
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?
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.
To amplify #Akram's answer - many people prefer the inner join syntax, since it then allows you to more easily distinguish between the join conditions (how the various tables in the FROM clause relate to each other) from the filter conditions (those conditions that should be used to reduce the overall result set. There's no difference between them in this circumstance, but on larger queries, with more tables, it may improve readability to use the inner join form.
In addition, once you start considering outer joins, you pretty well need to use the infix join syntax (left outer join,right outer join), so many find a form of symmetry in using the same style for inner join. There is an older deprecated syntax for performing outer joins in the WHERE clause (using *=), but support for such joins is dying out.