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.
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?
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(CurrentPerm) / NullIfZero(Max(CurrentPerm)) * 100))