My question might seem weird. But I need to know whether we can identify and seggregate the rows fetched from particular table in a query, which is formed by joining tables.
Please refer the below query if I am you are not clear with my question.
My requirement is to know the rows fetched from table 'rel' alone in the query.
SELECT rel.*
FROM rel, C
WHERE rel.col1 = C.col1
AND C.col1 NOT IN (SELECT R.col1 FROM R WHERE R.col2 = 'MN')
AND rel.col2= 'MN'
AND rel.col3= 'MN'
AND c.col2 ='MN';
Thanks,
Savitha
Since you are performing an INNER JOIN by using the comparison in the WHERE clause, all your records, by definition, are coming from the rel table.
Related
I am trying to use FULLTEXT search as a preliminary filter before fetching data from another table. Consecutive JOINs follow to further refine the query and to mix-and-match rows (in reality there are up to 6 JOINs of the main table).
The first "filter" returns the IDs of the rows that are useful, so after joining I have a subset to continue with. My issue is performance, however, and my lack of understanding of how the SQL query is executed in SQLite.
SELECT *
FROM mytbl AS t1
JOIN
(SELECT someid
FROM myftstbl
WHERE
myftstbl MATCH 'MATCHME') AS prior
ON
t1.someid = prior.someid
AND t1.othercol = 'somevalue'
JOIN mytbl AS t2
ON
t2.someid = prior.someid
/* Or is this faster? t2.someid = t1.someid */
My thought process for the query above is that first, we retrieve the matched IDs from the myftstbl table and use those to JOIN on the main table t1 to get a sub-selection. Then we again JOIN a duplicate of the main table as t2. The part that I am unsure of is which approach would be faster: using the IDs from the matches, or from t2?
In other words: when I refer to t1.someid inside the second JOIN, does that contain only the someids after the first JOIN (so only those at the intersection of prior and those for which t1.othercol = 'somevalue) OR does it contain all the original someids of the whole original table?
You can assume that all columns are indexed. In fact, when I use one or the other approach, I find with EXPLAIN QUERY PLAN that different indices are being used for each query. So there must be a difference between the two.
The query should be simplified to
SELECT *
FROM mytbl AS t1
JOIN myftstbl USING (someid) -- or ON t1.someid = myftstbl.someid
JOIN mytbl AS t2 USING (someid) -- or ON t1.someid = t2.someid
WHERE myftstbl.{???} MATCH 'MATCHME' -- replace {???} with correct column name
AND t1.othercol = 'somevalue'
PS. The query logic is not clear for me, so it is saved as-is.
i'm having a technical and syntax problem with JOINS in ORACLE.
If i have 7 tables, listed below:
FROM
QT_QTS.PLA_ORDEM_PRODUCAO pla,
qt_qts.res_tubo_austenitizacao aust,
qt_qts.res_tubo_revenimento1 res_rev1,
qt_qts.res_tubo_revenimento2 res_rev2,
limsprod.SAMPLE sp,
limsprod.test t,
limsprod.result r
I need to get ALL the data in the "limsprod.result r" table linked with similar corresponding data inside the qt_qts.res_tubo_austenitizacao aust, qt_qts.res_tubo_revenimento1 res_rev1 and qt_qts.res_tubo_revenimento2 res_rev2 tables.
How can I do this join using Oracle Database? I tried a left join, but it did not work.
It is impossible to answer that question. We have nothing but list of some tables. I'm not sure I'd even want to do that instead of you.
However, here's a suggestion: start with one table:
select * from limsprod.result r;
It'll return all rows. Then join it to another table:
select *
from limsprod.result r join qt_qts.res_tubo_austenitizacao aust on aust.id = r.id
and see what happens - did you get all rows you want? If not, should you add another JOIN condition? Perhaps an outer join? Don't move on to the third table until you sort that out. Once you're satisfied with the result, add another table:
select *
from limsprod.result r join qt_qts.res_tubo_austenitizacao aust on aust.id = r.id
join qt_qts.res_tubo_revenimento1 res_rev1 on res_rev1.idrr = aust.idrr
Repeat what's being said previously.
We are writing entity lambda expression query like this. But when we checked in profile. There were almost all the tables which were used in join returning entire table to the .net linq queries.
We have few transaction tables which has thousands of records. which is causing performance issue.
Please let us know if we can avoid table returning entire rows to .net
var result = (from f in f
join a in this.Context.a on f.primeryKey equals a.primeryKey
join d in this.Context.d on f.secondid equals d.secondid
join t in this.Context.t on d.thirdId equals t.thirdId
where t.isfoo && pfIds.Contains(a.fourthId.HasValue ? a.fourthId.Value : -1)
select f).Distinct().ToList();
Well, no real answer, for that I don't have enough info, but a few remarks to improve your query.
First remark: Don't do Contains and HasValue, because Linq won't SQL-ize these operations. I'm also not quite sure about the this.Context. stuff.
Second: NULL won't join in smart joins.
Third: Instead of selecting f, you'd typically select only a few fields of f that you need.
You'll need to rewrite your query. EF really needs to get all lines to utilize operator ? in order to evaluate value in a.fourthId column. I believe that
var result = (from f in f
join a in this.Context.a on f.primeryKey equals a.primeryKey
join d in this.Context.d on f.secondid equals d.secondid
join t in this.Context.t on d.thirdId equals t.thirdId
where t.isfoo && pfIds.Contains(a.fourthId)
select f).Distinct().ToList();
would meet your needs without necessary overhead, that evaluation seems to be superfluous.
Here is my query:
select count(*)
from email_prod_junc j
inner join trckd_prod t5 on j.trckd_prod_sk = t5.trckd_prod_sk
inner join prod_brnd b on t5.prod_brnd_sk = b.prod_brnd_sk
inner join email e on j.email_sk = e.email_sk
inner join dm_geography_sales_pos_uniq u on (u.emp_sk = e.emp_sk and u.prod_brnd_sk = b.prod_brnd_sk)
The explain plan says:
Cartesian Join between DM_GEOGRAPHY_SALES_POS_UNIQ and EMAIL_PROD_JUNC.
I don't understand why because there is a join condition for each table.
I solved this by adding the ORDERED hint:
select /*+ ordered */
I got the information from here
If you specify the tables in the order you want them joined and use this hint, Oracle won't spend time trying to figure out the optimal join order, it will just join them as they are ordered in the FROM clause.
Without knowing your indexes and the full plan, it's hard to say why this is happening exactly. My best guess is that EMAIL_PROD_JUNC and DM_GEOGRAPHY_SALES_POS_UNIQ are relatively small and that there's an index on TRCKD_PROD(trckd_prod_sk, prod_brnd_sk). If that's the case, then the optimizer may have decided that the Cartesian on the two smaller tables is less expensive than filtering TRCKD_PROD twice.
I would speculate that it happens because of the on (x and y) condition of the last inner join. Oracle probably doesn't know how to optimize the multi-statement condition, so it does a full join, then filters the result by the condition after the fact. I'm not really familiar with Oracle's explain plan, so I can't say that with authority
Edit
If you wanted to test this hypothesis, you could try changing the query to:
inner join dm_geography_sales_pos_uniq u on u.emp_sk = e.emp_sk
where u.prod_brnd_sk = b.prod_brnd_sk
and see if that eliminates the full join from the plan
The RIGHT JOIN on this query causes a TABLE ACCESS FULL on lims.operator. A regular join runs quickly, but of course, the samples 'WHERE authorised_by IS NULL' do not show up.
Is there a more efficient alternative to a RIGHT JOIN in this case?
SELECT full_name
FROM (SELECT operator_id AS authorised_by, full_name
FROM lims.operator)
RIGHT JOIN (SELECT sample_id, authorised_by
FROM lims.sample
WHERE sample_template_id = 200)
USING (authorised_by)
NOTE: All columns shown (except full_name) are indexed and the primary key of some table.
Since you're doing an outer join, it could easily be that it actually is more efficient to do a full table scan rather than use the index.
If you are convinced the index should be used, force it with a hint:
SELECT /*+ INDEX (lims.operator operator_index_name)*/ ...
then see what happens...
No need to nest queries. Try this:
select s.full_name
from lims.operator o, lims.sample s
where o.operator_id = s.authorised_by(+)
and s.sample_template_id = 200
I didn't write sql for oracle since a while, but i would write the query like this:
SELECT lims.operator.full_name
FROM lims.operator
RIGHT JOIN lims.sample
on lims.operator.operator_id = lims.sample.authorized_by
and sample_template_id = 200
Does this still perform that bad?