skew factor

Database
Enthusiast

Re: skew factor

Thenk you Pierre..

It happens some time when our database behave unexpectedly..

Even i checked practically and found that null values create same hash code ..so more nulls can cause high percentage of skew  on table.

New Member

Re: skew factor

Good Day!

 

I have 3 tables with very small skew: 1.47, 1.66 and 2.44. There are a few rows in each. But when I join this tables in select query, ViewPoint detect skew factor of SQL Query - more then 80%.

Can you tell me please how determines skew factor of SQL Query (select query). May be link on ducumentation?

 

Regards

Thanks

 

Ambassador

Re: skew factor

How few are a few rows in each table?

And how did you calculate the skew of thow tables?

 

You might have a default value causing the skew and when you join on that column skew will increase.

 

Viewpoint probably calculates skew as 

100 - (Avg(CurrentPermNullIfZero(Max(CurrentPerm)) 100))