Can you use something on the line of
Select * from table(cast(select * from tab1 inner join tab2)) inner join tab3
Take into account that what's inside the table(cast()) is something much more complex than a simple select involving a block like with test as (select) select *... etc.
I need a simple way to do this preferably without the need for a temporary table.
Thank you.
Database: Oracle 10g
LE:
I have something like
Select a.dummy1, a.dummy2, wm_concat(t2.dummy3)
from table1 a,
(with str as
(Select '1,2,3,4' from dual)
Select a.dummy1, t.dummy3
from table1 a
inner join
(Select regexp_substr (str, '[^,]+', 1, rownum) split
from str
connect by level <= length (regexp_replace (str, '[^,]+')) + 1) t
on instr(a.dummy2, t.split) > 0) t2
where a.dummy1='xyz'
group by a.dummy1, a.dummy2
The main idea is that column t2.dummy3 contains CSVs. Thats why i have select '1,2,3,4' from dual.
I need to find all rows that contain at least one of the values from str.
Using any kind of loop is out of the question because further i need to integrate this into a larger query used for a report in SSRS, and the tables needed for this are quite large (>1mil rows)
CAST seem completely irrelevant here. You use CAST to change the perceived datatype of an expression. Here, you're passing it a result set, not an expression, and you're not saying what datatype to cast to.
You should be able to simply remove the TABLE and CAST calls and do something like:
SELECT * FROM (SELECT * FROM tab1 INNER JOIN tab2 ON ...) INNER JOIN tab3 ON ...
e.g.
SELECT * FROM
(SELECT d1.dummy FROM dual d1 INNER JOIN dual d2 ON d1.dummy=d2.dummy) d12
INNER JOIN dual d3 ON d12.dummy = d3.dummy
Subquery factoring should work fine here as well.
WITH x AS (SELECT * FROM DUAL)
SELECT * FROM
(SELECT d1.dummy FROM x d1 INNER JOIN x d2 ON d1.dummy=d2.dummy) d12
INNER JOIN dual d3 ON d12.dummy = d3.dummy;
If you're having difficulty getting that kind of construct to work, try adding more detail to your question about specifically what you've tried and what error you're getting.
Yeah... i found the answer... i was just too SQL n00b to see it as it was right in front of me...
i just took the "with" statement outside of the query and it worked.
thank you so much for your help, it was your answer that led me to see my mistake :D
Something like:
with str as
(Select '1,2,3,4' from dual)
Select a.dummy1, a.dummy2, wm_concat(t2.dummy3)
from table1 a,
(
Select a.dummy1, t.dummy3
from table1 a
inner join
(Select regexp_substr (str, '[^,]+', 1, rownum) split
from str
connect by level <= length (regexp_replace (str, '[^,]+')) + 1) t
on instr(a.dummy2, t.split) > 0) t2
where a.dummy1='xyz'
group by a.dummy1, a.dummy2
Related
Does this query use correct Oracle syntax?
select * from ( ( ( dual a) ) ) where a.dummy = 'X';
It works in 11g and 12c but is it truly valid syntax? Or is this is just a compiler "mistake" that might be fixed in the future, causing the code the fail?
I doubt this is the correct syntax for the following reasons:
It doesn't seem to do anything other than add extra parentheses. Expressions like ((1+2)*3) can obviously benefit from nested parentheses but I don't see how they would ever help the FROM clause. And when I look at the above query the alias "a" looks out of scope.
I cannot find a valid path for this syntax in the SQL Language Reference syntax diagrams. On the other hand, it's easy to see how nested parentheses are permitted for expressions, conditions,
and subqueries. Expressions, conditions, and subqueries are recursive and can contain parentheses, but a join clause is not recursive.
I worry about this because there have been similar cases where invalid syntax worked in one release and then failed in the next. For example: select (select count(*) from (select * from scott.emp where ename = dual.dummy)) from dual;. That query worked in 10.2.0.1.0 but stopped working in later versions because table references are scoped to only one level deep.
The original query has a bad style but it's not worth changing our production queries unless there is a real problem with it.
Is the query invalid? Or is there some legitimate reason for that syntax, or is there some path in the syntax diagrams I'm missing?
It is legal syntax to use parenthesis in a join clause in a FROM, and the parentheses do have an effect.
Consider this query:
WITH table_a AS ( SELECT rownum id FROM DUAL CONNECT BY LEVEL <= 30),
table_b as ( SELECT rownum id FROM DUAL CONNECT BY LEVEL <= 20),
table_c AS ( SELECT rownum id FROM DUAL CONNECT BY LEVEL <= 10)
SELECT a.id, b.id, c.id
FROM table_a a left join ( table_b b inner join table_c c ON c.id = b.id ) ON b.id = a.id
ORDER BY 1,2,3;
The parenthesis allow you to do an inner join of tables b and c and then outer join that to a.
Without the parenthesis, trying to express that as a left join would be impossible. You either wouldn't get rows 11-30 from table a or else rows 11-20 of table c would be nulls (depending on how you tried to do it).
Note that the above query is equivalent to:
WITH table_a AS ( SELECT rownum id FROM DUAL CONNECT BY LEVEL <= 30),
table_b as ( SELECT rownum id FROM DUAL CONNECT BY LEVEL <= 20),
table_c AS ( SELECT rownum id FROM DUAL CONNECT BY LEVEL <= 10)
SELECT a.id, b.id, c.id
FROM table_b b inner join table_c c on c.id = b.id right join table_a a on a.id = b.id
ORDER BY 1,2,3;
, which doesn't require parenthesis. So if you really want to avoid using parentheses in the FROM clause, you usually can do so. Personally, I prefer the LEFT JOIN method with parentheses instead of a RIGHT JOIN.
According to my reading of the syntax diagram for a SELECT statement, putting parentheses around a table reference in a SELECT statement is not allowed. As to whether or not Oracle might "fix" things in a way that would make this invalid, I have no way of knowing but I consider it unlikely. YMMV.
Best of luck.
EDIT
Just for fun I thought I'd put down my reading of the syntax diagram:
As other have noted, parentheses are allowed around a join_clause, but dual a is not a join_clause. Rather, it is a query_table_expression which is part of a table_reference. dual a cannot be a join_clause - to be such it would have to be followed by an inner_join_clause (e.g. INNER JOIN) or an outer_join_clause (e.g. LEFT OUTER JOIN, RIGHT OUTER JOIN or FULL OUTER JOIN), which it is not. Per the syntax diagram parentheses are not allowed around a query_table_expression unless the query_table_expression is preceded by ONLY, and in OP's query dual a is not preceded by ONLY. Thus I conclude that per the Oracle syntax diagrams ( ( (dual a) ) ) is not syntactically correct; however, the database seems to disagree. :-)
Additional to join_clause the subquery may be nested.
So this is perfect valid syntax
(((select * from dual)));
This provides the clue to the validity of the synax of the questioned query.
select * from (((dual)));
Starting with the select we go to query_block
select --> subquery --> query_block
query_block expands to
SELECT * FROM table_reference
From table_reference we step down to (nested) subquery, which can be further nested.
table_reference --> query_table_expression --> ( subquery )
So keep expanding subquery to get required nesting and finaly choose TABLE as the expansion of the query_table_expression
But as MT0 and others noted, this unfortunately don't lead to the e3xpected result. The maximal legal query is
select * from (((select * from dual)));
I have this sql query delivered from a customer which we need to performance optimize.
Is there anyone that can point me in the right direction to where to start looking for optimizing the following query?
The query on my local machine takes about 6-7 seconds, but on the users it´s about 30 seconds, It executes on a mssql 2008r2
Thanks!
var query = #"
DECLARE #SearchString nvarchar(250)
set #SearchString = '1811820001'
;with BaseSelectorCTE (ID) as
(
SELECT ID FROM BaseCases b
where
b.CPR like #SearchString
OR (b.FirstName + ' ' + b.LastName) like #SearchString
OR b.CustomerInfo_InstitutionName like #SearchString
UNION
Select ID from FlexjobCase
where Kommune like #SearchString
UNION
Select ID from DisabledAssistantCase
where Kommune like #SearchString
UNION
Select ID from AdultStudentCase
where Kommune like #SearchString
UNION
Select ID from DiseaseCase
where Kommune like #SearchString
UNION
Select ID from MaternityCase
where Kommune like #SearchString
UNION
Select ID from MiscellaneousCase
where Kommune like #SearchString
UNION
Select ID from WageSubsidyCase
where Kommune like #SearchString
UNION
Select w.ID from WageSubsidyCase w inner join JobCenters j on
w.JobcenterID = j.ID
where
j.Name like #SearchString
UNION
Select a.ID from AdultStudentCase a inner join JobCenters j on
a.JobcenterID = j.ID
where
j.Name like #SearchString
)
--
-- Select BaseCases mapped to result type
--
,ResultSelectorCTE AS
(
select
bc.Id as CaseID,
bc.ChildCaseName,
bc.CPR,
bc.FirstName,
bc.LastName,
bc.CustomerInfo_CustomerInfoID as CustomerInfoID,
bc.CustomerInfo_InstitutionName as InstitutionName,
bc.CaseDeadline,
bc.StatusID,
cs.Name as [StatusName],
cs.Owner as [StatusOwner],
bc.MetaData_Updated as [LastChange],
bc.LastActionDay,
,CASE bc.StatusID WHEN 9 THEN 1 ELSE 0 END as SidstePeriodeSoegt
from BaseCases bc
inner join CaseStatus cs ON
bc.StatusID = cs.ID
inner join BaseSelectorCTE bsCTE ON
bc.ID = bsCTE.ID
)
select * from (Select *, ROW_NUMBER() Over(Order By ##version , CASE WHEN StatusID = 9 then 2 ELSE 1 END, CaseDeadline ASC,
SidstePeriodeSoegt)
As rownum from ResultSelectorCTE where 1=1 AND StatusOwner <> 2 AND StatusOwner <> 3
AND SUBSTRING(CPR, 0, 3) BETWEEN 26-08-2014 AND 26-08-2015) As Result
where rownum Between ((1 - 1) * 100 + 1) AND (1 * 100);
Yes, the query execution plan:
The SQL Server Database Engine can display how it navigates tables and uses indexes to access or process the data for a query or other DML statement, such as an update. This is a display of an execution plan. To analyze a slow-running query, it is useful to examine the query execution plan to determine what is causing the problem.
Without knowing anything, start by losing the wildcards (*) sign. It's bad almost always as you are just saying, send everything and forgetting to actually review it.
Then, format your code correctly, CTE's are great, simplifies code, but it beats the purpose if your selects look like spaghetti, this has nothing to do with performance though.
Also, I had many times when UNION ALL outperformed UNION and I din't really think if duplicates were a problem or not, so you might want to look into that.
You didn't say if you are running it from Management Studio, are you on a local or remote server, how do the CTE's perform individually, etc. Context is king on this.
Hope this helps.
I need to make a conversion from Oracle SQL to PostgreSQL.
select * from table1 inner join table2 on table1.id = table2.table1Id
where table1.col1 = 'TEST'
and rownum <=5
order by table2.col1
If I delete and rownum <=5 and put at the end limit 5, there are differences between the 2 dialects. In Oracle, first are selected the 5 elements, and after that, they are sorted by table2.col1 . In Postgres, first all the list is sorted, and AFTER there are selected the first 5 elements.
How can I obtain the same result in Postgres as in Oracle?
Thanks!
To get the behavior you desire, you can use a subquery like this:
SELECT * FROM (
SELECT table1.col1 as t1col1, table2.col1 as t2col1
FROM table1 INNER JOIN table2 ON table1.id = table2.table1Id
WHERE table1.col1 = 'TEST'
LIMIT 5
) AS sub
ORDER BY t2col1;
I named the columns there because in your example both tables had a col1.
Note however that without any ordering on the inner query, the selection of 5 rows you get will be purely random and subject to change.
Depending on the version you are using, PostgreSQL 8.4 and above have Window functions. Window function ROW_NUMBER() is capable of implementing the functionality of Oracle pseudo column rownum.
select row_number() over() as rownum,* from table1 inner join table2 on table1.id = table2.table1Id where table1.col1 = 'TEST' and rownum <=5 order by table2.col1;
Here is my query,
SELECT ID As Col1,
(
SELECT VID FROM TABLE2 t
WHERE (a.ID=t.ID or a.ID=t.ID2)
AND t.STARTDTE =
(
SELECT MAX(tt.STARTDTE)
FROM TABLE2 tt
WHERE (a.ID=tt.ID or a.ID=tt.ID2) AND tt.STARTDTE < SYSDATE
)
) As Col2
FROM TABLE1 a
Table1 has 48850 records and Table2 has 15944098 records.
I have separate indexes in TABLE2 on ID,ID & STARTDTE, STARTDTE, ID, ID2 & STARTDTE.
The query is still too slow. How can this be improved? Please help.
I'm guessing that the OR in inner queries is messing up with the optimizer's ability to use indexes. Also I wouldn't recommend a solution that would scan all of TABLE2 given its size.
This is why in this case I would suggest using a function that will efficiently retrieve the information you are looking for (2 index scan per call):
CREATE OR REPLACE FUNCTION getvid(p_id table1.id%TYPE)
RETURN table2.vid%TYPE IS
l_result table2.vid%TYPE;
BEGIN
SELECT vid
INTO l_result
FROM (SELECT vid, startdte
FROM (SELECT vid, startdte
FROM table2 t
WHERE t.id = p_id
AND t.startdte < SYSDATE
ORDER BY t.startdte DESC)
WHERE rownum = 1
UNION ALL
SELECT vid, startdte
FROM (SELECT vid, startdte
FROM table2 t
WHERE t.id2 = p_id
AND t.startdte < SYSDATE
ORDER BY t.startdte DESC)
WHERE rownum = 1
ORDER BY startdte DESC)
WHERE rownum = 1;
RETURN l_result;
END;
Your SQL would become:
SELECT ID As Col1,
getvid(a.id) vid
FROM TABLE1 a
Make sure you have indexes on both table2(id, startdte DESC) and table2(id2, startdte DESC). The order of the index is very important.
Possibly try the following, though untested.
WITH max_times AS
(SELECT a.ID, MAX(t.STARTDTE) AS Startdte
FROM TABLE1 a, TABLE2 t
WHERE (a.ID=t.ID OR a.ID=t.ID2)
AND t.STARTDTE < SYSDATE
GROUP BY a.ID)
SELECT b.ID As Col1, tt.VID
FROM TABLE1 b
LEFT OUTER JOIN max_times mt
ON (b.ID = mt.ID)
LEFT OUTER JOIN TABLE2 tt
ON ((mt.ID=tt.ID OR mt.ID=tt.ID2)
AND mt.startdte = tt.startdte)
You can look at analytic functions to avoid having to hit the second table twice. Something like this might work:
SELECT id AS col1, vid
FROM (
SELECT t1.id, t2.vid, RANK() OVER (PARTITION BY t1.id ORDER BY
CASE WHEN t2.startdte < TRUNC(SYSDATE) THEN t2.startdte ELSE null END
NULLS LAST) AS rn
FROM table1 t1
JOIN table2 t2 ON t2.id IN (t1.ID, t1.ID2)
)
WHERE rn = 1;
The inner select gets the id and vid values from the two tables with a simple join on id or id2. The rank function calculates a ranking for each matching row in the second table based on the startdte. It's complicated a bit by you wanting to filter on that date, so I've used a case to effectively ignore any dates today or later by changing the evaluated value to null, and in this instance that means the order by in the over clause needs nulls last so they're ignored.
I'd suggest you run the inner select on its own first - maybe with just a couple of id values for brevity - to see what its doing, and what ranks are being allocated.
The outer query is then just picking the top-ranked result for each id.
You may still get duplicates though; if table2 has more than one row for an id with the same startdte they'll get the same rank, but then you may have had that situation before. You may need to add more fields to the order by to break ties in a way that makes sens to you.
But this is largely speculation without being able to see where your existing query is actually slow.
I have a co worker who wrote the following query. The first one works and the second one does not. Also if you remove the aggregate function from the subquery, it works. The oracle optimizer is doing something weird. Any thoughts? Running in SQL Developer 3.1 against 11.1.0.6.0 64 bit.
This works:
SELECT
a.fd_customer_key
, b.fd_customer_key
, b.counter
FROM FETCH_CUSTOMER a
, (select fd_customer_key, count(*) as counter from fetch_customer_order group by fd_customer_key) b
where a.fd_customer_key = b.fd_customer_key (+)
and b.counter is null
This doesn’t:
SELECT
a.fd_customer_key
, b.fd_customer_key
, b.counter
FROM FETCH_CUSTOMER a
, (select fd_customer_key, count(*) as counter from fetch_customer_order group by fd_customer_key) b
where a.fd_customer_key = b.fd_customer_key (+)
and b.fd_customer_key is null
Actually yes, both of the queries you provided are supposed to wrok the same way, but if i understand your need well, you are trying to select the fd_customer_key which has no Order?
I suggest the following query for your need, its more simple and less consuming :
SELECT a.fd_customer_key
FROM FETCH_CUSTOMER a
WHERE NOT EXISTS (SELECT 1
FROM fetch_customer_order b
WHERE a.fd_customer_key = b.fd_customer_key)
It seems like you are trying to make an anti-join (find the rows from FETCH_CUSTOMER that have no corresponding rows in FETCH_CUSTOMER_ORDER).
With Oracle you do not have to use this clever OUTER JOIN trick to write an anti-join, you could use a NOT IN or NOT EXISTS operator and let the optimizer find the best plan. This will be just as efficient and easier to read.
Anyway, I can't reproduce your findings, here's my setup:
CREATE TABLE a (ID NUMBER PRIMARY KEY);
CREATE TABLE b (a_id NUMBER NOT NULL, DATA VARCHAR2(30));
INSERT INTO a (SELECT object_id FROM all_objects);
INSERT INTO b (SELECT object_id, object_name
FROM all_objects WHERE object_type = 'VIEW');
SELECT a.id, b.a_id, b.cnt
FROM a, (SELECT a_id, COUNT(*) cnt FROM b GROUP BY a_id) b
WHERE a.id = b.a_id (+)
AND b.cnt IS NULL;
SELECT a.id, b.a_id, b.cnt
FROM a, (SELECT a_id, COUNT(*) cnt FROM b GROUP BY a_id) b
WHERE a.id = b.a_id (+)
AND b.a_id IS NULL;
You will find that both queries return rows. What is your DB version?