I'm using Oracle 11g. I have a query that joins local table with remote tables using db links. I want the driving table to be the remote table as I primarily filter using remote table to get a few rows. I then want to join them with local table.
The problem is the optimizer ignores ORDERED and INDEX hints and does a full table scan of the local table. I am using the right indexes and have generated statistics. I run the queries individually with each table they use the correct indexes, but with the join, the local table always does a full table scan and acts as the driving table.
SELECT /*+ INDEX_RS_ASC(l) */
*
FROM remote_table#mylink r
JOIN local_table l USING (cont_id)
WHERE r.PRIME_VENDOR_ID = '12345'
Related
I know that ROWID is distinct for each row in different tables.But,I am seeing somewhere that two tables are being merged using rowid.So,I also tried to see it,but I am getting the blank output.
I have person table which looks as:
scrowid is the column which contains rowid as:
alter table ot.person
add scrowid VARCHAR2(200) PRIMARY KEY;
I populated this person table as:
insert into ot.person(id,name,age,scrowid)
select id,name, age,a.rowid from ot.per a;
After this I also created another table ot.temp_person by same steps.Both table has same table structure and datatypes.So, i wanted to see them using inner join and I tried them as:
select * from ot.person p inner join ot.temp_person tp ON p.scrowid=tp.scrowid
I got my output as empty table:
Is there is any possible way I can merge two tables using rowid? Or I have forgotten some steps?If there is any way to join these two tables using rowid then suggest me.
Define scrowid as datatype ROWID or UROWID then it may work.
However, in general the ROWID may change at any time unless you lock the record, so it would be a poor key to join your tables.
I think perhaps you misunderstood the merging of two tables via rowid, unless what you actually saw was a Union, Cross Join, or Full Outer Join. Any attempt to match rowid, requardless of you define it, doomed to fail. This results from it being an internal definition. Rowid in not just a data type it is an internal structure (That is an older version of description but Oracle doesn't link documentation versions.) Those fields are basically:
- The data object number of the object
- The data block in the datafile in which the row resides
- The position of the row in the data block (first row is 0)
- The datafile in which the row resides (first file is 1). The file
number is relative to the tablespace.
So while it's possible for different tables to have the same rowid, it would be exteremly unlikely. Thus making an inner join on them always return null.
In my Java program, I am trying to take values from a PostgreSQL database and using this data I am using a Select query with an Oracle database.
Problem is, it is taking too much time to complete this task. First I am fetching data from Postgres table and load into variable.
Then with this variable I am executing a select query against an Oracle table.
But I want to make this process faster. Is it possible to perform this task in one query that takes data from PostgreSQL table and fetch data from Oracle table?
Postgres statement:
select filial_name
into f_name
from branch
where id=1;
Oracle statement:
select sum(credit)
from balance
where filial_n = f_name;
Above process continues in loop.
If you have to run a massive join between an Oracle table and a PostgreSQL table, that is never going to be very fast.
But you can do much better than performing the join in your application by defining an oracle_fdw foreign table in PostgreSQL and performing the join in PostgreSQL.
i have a slow query whose structure is
select
fields
from
table
join
manytables
join (select fields from tables) as V1 on V1 on V1.field = ....
join (select fields1 from othertables) as V2
join (select fields2 from moretables) as V3
The select subqueries in the last 3 joins are relatively simple but joins agains the, take time. If they were phisical tables it would be much better.
So i found out that i could turn the subqueries to indexed views or to temp tables.
By temp table i do not mean a table who is written hourly like explained here,
but a temp table who is created before the query execution
Now my doubt comes from the fact that indexed views are ok in datawarehouses since they impact the performance. This db is not a datawarehouse but a production db of a non data intense application.
But in my case the above query is executed not often, even if the underlaying tables (the tables whose data would become part of the indexed view) are used more often.
In this case is it ok to use indexed views? Or shuold i favor temp table?
Also table variable with primary key keyword is an alternative.
how to join two tables in oracle on blob column
when this query is executed "SQL command not properly ended" error message is appearing
select name,photo
from tbl1 join tbl2 on tbl1.photo = tbl2.photo
First, it seems very very odd to have a design where you are storing the same blob in two different tables and very odd that you would want to join on an image. That doesn't seem like a sensible design.
You've tagged this for Oracle 8i. That is an ancient version of Oracle that didn't support the SQL 99 join syntax. You would need to do the join in the where clause instead. You can't directly test for equality between two blob values. But you can use dbms_lob.compare
select name,photo
from tbl1,
tbl2
where dbms_lob.compare(tbl1.photo, tbl2.photo) = 0
This will be rather hideous from a performance perspective. You'll have to compare every photo from tbl1 against every photo from tbl2 and comparing two lobs isn't particularly quick. If you are really intent on comparing images, you are probably better off computing a hash, storing that in a separate column that is indexed, and then comparing the hashes rather than comparing the images directly.
The code:
SELECT
name, photo
FROM
tbl1 T1
INNER JOIN
tbl2 T2
ON
T1.photo = T2.photo
If not running fine, you would have to make few changes in your TABLE structure:
1. ...Add a new TABLE named as IMAGES having columns (image_id, image_blob)
2. ...And then you you would have to change the:
tbl1's blob and tbl2's blob to image_id
3. ...Then perform the JOIN on the basis of COLUMN named as image_id
NOTE: You can not perform GROUP BY, JOIN(any JOIN), CONCAT operations on BLOB datatype
SUGGESTION: save the Paths to images in the DATABASE and save the IMAGES somewhere on that SERVER's Directory (As saving images in BLOB in the DATABASE is not a good practice..... To ensure what i said VISIT HERE)
I have two tables table1 in local system and table2 on another system. I created database link to table2 in local sytem I.e table2#anothersystem
I have two columns in both tables ID (number) & NAME (varchar). I want to execute any query on table1 such that after it's execution in table1 it will also be identically executed in table2.
In short I want to keep table1=table2. can anybody suggest trigger for it in Oracle 11g
As #justin-cave already mentioned, using triggers is definitely not the way to go. I'd opt for a materialized view (the cheap option). Check Oracle materialized view question for a starting point. When you have the appropriate license you could create a logical or physical standby database, or other Oracle-provided data replication options.