Hash Join require Full Table Scan

Posted by Pedro Magalhaes on Stack Overflow See other posts from Stack Overflow or by Pedro Magalhaes
Published on 2010-04-09T02:20:15Z Indexed on 2010/04/09 2:23 UTC
Read the original article Hit count: 450

Filed under:

joins

|

database

So, I want to know if to make a Hash Join between two tables is necessary to make a full table scan on the collumns?

If i want to join COL1 wiht COL2, and COL1 is smaller, the It makes a full scan in COL1 creating a Hashmap then makes a full scan in COL2 using the sabe hash function.

Is this correct?

© Stack Overflow or respective owner

Related posts about joins

Rails Joins and include columns from joins table

as seen on Stack Overflow - Search for 'Stack Overflow'
I don't understand how to get the columns I want from rails. I have two models - A User and a Profile. A User :has_many Profile (because users can revert back to an earlier version of their profile): > DESCRIBE users; +----------------+--------------+------+-----+---------+----------------+ |… >>> More
SQL Joins on varchar fields timing out

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi, I have a join which deletes rows that match another table but the joining fields have to be a large varchar (250 chars). I know this isn't ideal but I can't think of a better way. Here's my query: DELETE P FROM dbo.FeedPhotos AS P INNER JOIN dbo.ListingPhotos AS P1 ON P.photo = P1.feedImage INNER… >>> More
Joins and UI Binding with the Entity Framework

as seen on Internet.com - Search for 'Internet.com'
Learn how to build queries with the Entity Framework that involve multiple tables as well as binding in the UI with the EntityDataSource. >>> More
Fetching Data from Multiple Tables using Joins

as seen on Internet.com - Search for 'Internet.com'
Applying normalization to relational databases tends to promote better accuracy of queries, but it also leads to queries that take a little more work to develop, as the data may be spread amongst several tables. In today's article, we'll learn how to fetch data from multiple tables by using joins. >>> More
App Engine joins the Google over IPv6 Program

as seen on Google Code - Search for 'Google Code'
The Google over IPv6 program allows ISPs with good connectivity to request IPv6 access for most Google services. In about a week, we'll be adding Google App Engine... >>> More

Related posts about database

SQL SERVER Retrieve and Explore Database Backup without Restoring Database Idera virtual database

as seen on Dot net Slackers - Search for 'Dot net Slackers'
I recently downloaded Ideras SQL virtual database, and tested it. There are a few things about this tool which caught my attention.My ScenarioIt is quite common in real life that sometimes observing or retrieving older data is necessary; however, it had changed as time passed by. The full database… >>> More
Cloning A Database On The Same Server Using Rman Duplicate From Active Database

as seen on Oracle Blogs - Search for 'Oracle Blogs'
To clone a database using Rman we used to require an existing Rman backup, on 11g we can clone databases using the "from active" database option. In this case we do not require an existing backup, the active datafiles will be used as the source for the clone. In order to clone with the source database… >>> More
cPickle ImportError: No module named multiarray

as seen on Stack Overflow - Search for 'Stack Overflow'
Hello, I'm using cPickle to save my Database into file. The code looks like that: def Save_DataBase(): import cPickle from scipy import * from numpy import * a=Results.VersionName #filename='D:/results/'+a[a.find('/')+1:-a.find('/')-2]+Results.AssType[:3]+str(random.randint(0,100))+Results.Distribution+"… >>> More
SQL SERVER – 2008 – Introduction to Snapshot Database – Restore From Snapshot

as seen on SQL Authority - Search for 'SQL Authority'
Snapshot database is one of the most interesting concepts that I have used at some places recently. Here is a quick definition of the subject from Book On Line: A Database Snapshot is a read-only, static view of a database (the source database). Multiple snapshots can exist on a source database and… >>> More
OTN ???? ?????? ???????

as seen on Oracle Blogs - Search for 'Oracle Blogs'
Database ?? Database ??????? Database ?????????? Java WebLogic Server/????????·???? SOA/BPM/????? ???????/???? ID??/?????? ?????EPM/BI EPM/BI ??????? EPM/BI ???? OS/??? ???? ????? MySQL Database ?? ???? ?? ????????? ??? ?? ORACLE MASTER… >>> More