If i have a table T1 and a table T2. Table T1 is having 100 rows and table T2 is having 20 rows. When performing a Hash join ,which table should be used to make the hash table ,the larger one or the smaller one and why ?IF the data set is too small for considerations then please conser table T1 with 10 million of rows and table T2 with 1 million of rows.
View 11 Replieswhat is Hash join?how it is different from inner join?what is the sign used for inner join?(eg: like the (+) sign used for outer join)?
View 1 Replies View RelatedWhat is the difference between Hash join and Nested Loops in pl / sql?
View 1 Replies View RelatedI tried to search on google for "Hash Join" And "Sort Merge". But unfortunatly i am unable to understand that articles. "Hash join" And "Sort Merge".
View 3 Replies View RelatedI want to know how the Oracle optimizer choose joins and apply them while executing the query. So that I will insure about optimizer join before writing any query.
View 2 Replies View RelatedI have a question.
When and Where HASH VALUE for a given SQL statement get generated?
Is it true that the SQL hash is computed on the SQL text only ?
View 4 Replies View RelatedI see one of my SQL's which is ran by the user on a 10.2.0.3 database changing its SQL_ID after some runs even if the query is not changed a bit! However the HASH VALUE for this query remains the same.
how a same query can have different SQL_ID's but same HASH_VALUE?
Note: Statistics are not modified on the base tables of this query.
I am facing a problem in fetching / updating records from a customer details table having around 20 million records. The table contains around 30 fields with 'MOBILE_NO' as primary key. most of the queries are having 'mobile_no' in where clause .I am planning to hash partition that table using mobile_no column as there is no other column available which can be used for partition.
clarify whether creating hash partition on such key would increase performance of data extraction as I have read on net that hash partitioning is not effective for performance tuning.
I see that one of my queries from an application time is spending most of its time in the hash group by. I'm running Oracle 11g with a quarter rack exadata appliance. Is there a better way to run or design this table? query:
SELECT COUNT(*)
FROM (
SELECT "DDTMDAY", "MRKTNM", "BSMNM", "BSCNM", "CLNM", "CSCDNM", "BTSID", "SECTSEQID", "BNDID", "FAID", SUM("VATTCNT"), SUM("VMBLORGCNT"), SUM("VMBLTERCNT"), SUM("VSILENTRETRYCNT"), SUM("VCUSTBLKCNT"), SUM("VAXSFCNT"), SUM("VCEBLKCNT"), SUM("VWCDBLKCNT"), SUM("VT1BHLBLKCNT"), SUM("VPWRBLKCNT"), SUM("VNONBTSEQBLKCNT"), SUM("VSFULCALLCNT"), SUM("VDRPCALLCNT"),
[code]...
Lets say I have three tables t1 and t2 and t3.
SELECT * FROM T1;
Id
____
1
2
3
4
SELECT * FROM T2;
Id
____
1
SELECT * FROM T3;
Id
____
1
Now when data exists in T2 and T3, I want to return only the records in T1 that match the records in T2 and T3 which is basically a normal join
select t1.id from t1, t2,t3 where t1.id = t2.id and t1.id = t3.id
However when there are no records in T2 or T3, I want to return all records in T1 i.e 1,2,3,4
One way of doing that is using the not exists clause
select * from t1 where not exists ( select null from t2 where t2.Id != t1.id) and not exists ( select null from t3 where t1.Id != t3.id)
Is there a better way of doing this in sql ?
A basic select and group by query I am optimising for my Database course has returned results that indicate it will perform better on a clustered index when returning a smaller number of rows (5% of the largest table) and on a hash clustered index when returning higher volumes (50% and 80%). I understand that it is possible to use more than one index type on a table to improve performance, but I am struggling to understand how I might establish a hash cluster and a cluster on the same table? and then use hints to drive the query down one access path or the other.
Site admin - this site is a very useful resource.
I created a single table hash cluster like this :
create tablespace mssm datafile 'c:appmssm01.dbf' size 100m
segment space management manual;
create cluster hash_cluster_4k
( id number(2) )
size 8192 single table hash is id hashkeys 4 tablespace mssm;
-- Created a table in cluster with row size such that only one record fits one block and inserted 5 records each with a distinct key value
CREATE TABLE hash_cluster_tab_8k
( id number(2) ,
txt1 char(2000),
txt2 char(2000),
txt3 char(2000)
)
CLUSTER hash_cluster_8k( id );
[code]....
If I issue the same query after creating unique index on hash_cluster_tab(id), the execution plan shows hash access and single I/O (cr = 1).Does it mean that to have single I/o in a single table hash cluster, we have to create unique index? Won't it create additional overhead of maintaining an index?
What is the second I/O needed for in case unique index is absent?
I have a existing non partition table with more than 100 million records,planning to re design using Hash partition.This table doesn't has any range column to do range partitioning.
Table has 40 columns with a Primary Key on two columns (guest_sales_Id ,Version Flag). guest_sales_Id is unique for entire table but with anopther column version Flag declared as Primary key.(Version Falg will have only two distinct values in entire table)
If i do hash partition,do i need to declare on two columns which are declared ad Primary key ?If i use only guest_sales_id to declare hash prtition any issues ?
I created the 32 hash partition on a fact table. Based on hash parititon technique it should evenly distribute data accross the different partition.But when i analyze the table and check the distribution its not at all even.
P_Name Tabspace num_Rows
SYS_P21TBS_TBS0
SYS_P22TBS_TBS0
SYS_P23TBS_TBS0
[Code]....
note we need to decrypt the data which is encrypted using dbms_crypto.hash algorithm. it is possible to decrypt dbms_crypt.hash
eg
SQL> select DBMS_CRYPTO.hash(utl_raw.cast_to_raw('Foo'), 3) FROM dual;
DBMS_CRYPTO.HASH(UTL_RAW.CAST_TO_RAW('FOO'),3)
--------------------------------------------------------------------------------
201A6B3053CC1422D2C3670B62616221D2290929
Getting an ORA-00060 in our database. This is the alert log:
Wed Nov 10 08:01:54 2010
Global Enqueue Services Deadlock detected. More info in file
/opt/oracle/admin/ngboot/bdump/ngboot1_lmd0_13119.trc.
This is part of the lmd file:
oprocp : (nil)
opid : 0
group lock owner : (nil)
xid : 0000-0000-00000000
dd_time : 0.0 secs
dd_count : 0
timeout : 0.0 secs
[Code] ......
How do I find the SQL causing this? I have the hash value of 3180952482. should I open up en SR as this i logged in an lmd trace?
With this table in local and remote database via a DBLink
CREATE TABLE PICTURES (
ID NUMBER(12),
PICNAME VARCHAR2(20),
PICTURE BLOB
);
How come I can get the hash of the picture column fine like this:
SELECT dbms_crypto.hash@dbLink(PICTURE, 3)from SCHEMA1.PICTURES@dbLink;
but I can't do it in a union with the local database?
SELECT dbms_crypto.hash@dbLink(PICTURE, 3)from SCHEMA1.PICTURES@dbLink
UNION
SELECT dbms_crypto.hash(PICTURE, 3)FROM SCHEMA1.PICTURES;
gives "ORA-06553: PLS-564: lob arguments are not permitted in calls to remote server"
I was reading the documentation for oracle 11gr2, with reference to URL>.....
The following examples show how to correctly choose the cluster key and set the HASH IS, SIZE, and HASHKEYS parameters. For all examples, assume that the data block size is 2K and that on average, 1950 bytes of each block is available data space (block size minus overhead).Note that 34 hash keys are assigned for each data block
how they arrive at 34 hash keys because another portion of the document states
This space determines the maximum number of cluster or hash values stored in a data block. If SIZE is not a divisor of the data block size, then Oracle Database uses the next largest divisor.
if that is the case, then number of hash keys should be 1900/55 = 34.55 which should have rounded up to 35.
At moment we use range-hash partitioning of a large dimension table (dimension model warehouse) table with 2 levels - range partitioned on columns only available at bottom level of hierarchy - date and issue_id.
Result is a partition with null value - assume would get a null partition in large fact table if was partitioned with reference to the large dimension.Large fact table similarly partitioned date range-hash local bitmap indexes
Suggested to use would get automatic partition-wise joins if used reference partitioningWould have thought would get that with range-hash on both dimension.
I have to create a hash partition on fact tables.. we can use temp tablespace or permanent tablespace.
View 10 Replies View RelatedWhile trying partition exchange feature of Oracle with 2 hash partitioned tables, I come to know that I can't directly exchange partitions between 2 partitioned tables
I have two hash partitioned tables , so to move partition data from one table to another will include-
1) Exchange from partitioned table to non-partitioned table.
2) exchange from non-partitioned table to new partitioned table.
But I am not sure in which hash partition my data will go in new partitioned table (data need to be moved has single key value on basis of which tables are partitioned),
i want to know the difference between Left outer join Vs. Right outer join? Its like which join is safer to use or is there any recommendations to use any join?
View 6 Replies View RelatedAt present we have a non partitioned table.
Can we apply redefinition and create range partition and hash sub partition on it?
I need query for below my request...This is our sample text
Original text: ,UNDRLYNG_AST_NM,"NEXTERA ENERGY, INC.",
output Replace text:,UNDRLYNG_AST_NM,"NEXTERA ENERGY~ INC."
i want replace ',' to '~' between the alphabetic or alphabetic with space
Can I add range sub partition to a hash partition table. Example like this.
CREATE TABLE test
(
test_id VARCHAR2(10 ) ,
test_TYPE VARCHAR2(5) ,
CREATE_DATE date
)
partition by hash (test_id, test_type)
Partitions 3
SUBPARTITION BY RANGE (CREATE_DATE);
When Tried, I am getting syntax error as invalid option.
RDBMS - 11.1.0.7, I it possible to convert indexes of a non-partitioned table to hash partitioned indexes by retaining table as non-partitioned?
If yes, is this what it is Creating a Hash-Partitioned Global Index - can be created for partitioned and non-partitioned tables?
I want to create a query with only the junction of these two queries:
- select id_utilizador,nbeneficiario,nome from adm_utilizadores a WHERE exists ( select 1 from adm_util_grupos b where
a.id_utilizador = b.id_utilizador and b.id_grupo = '1') ;
- SELECT b.*,rownum as row_num FROM ADM_UTILIZADORES b ORDER BY $sidx $sord
WHERE row_num BETWEEN $start AND $end";
Virtually want id_utilizador, nome, and nbeneficiario, I can get the first query, ordered me returning the first 10.
I am new to sql..
I need to join 2 tables based on first match.. I cldnot use distinct on the result, as distinct work with entire row..
I cant use group by as well, since for group by hv to select all the columns which we need to display
I have 2 tables SEC_MASTER_HISTA and SEC_MASTER_HISTB.
Now, I need to compare the data of the two tables column-wise.
Ideally the 2 tables should have the same security_alias values but in my case they do not as the two tables belong to 2 diff client models. There is however a main SECURITY_MASTERA and SECURITY_MASTERB tables which have the security_alias recorded and a primary_asset_id column value which can act as a link between SEC_MASTER_HISTA and SEC_MASTER_HISTB. But, I have not been able to figure out the exact query which will be ideal.
Attached are the table structures and the data it contains.
Note: I need to compare the Coupon and Freq column values of SEC_MASTER_HISTA and SEC_MASTER_HISTB.