When should the statistics be collected?
Here are some excellent guidelines on when to collect statistics:
· All Non-Unique indices
· Non-index join columns
· The Primary Index of small tables
· Primary Index of a Join Index
· Secondary Indices defined on any join index
· Join index columns that frequently appear on any additional join index columns that frequently appear in WHERE search conditions
· Columns that frequently appear in WHERE search conditions or in the WHERE clause of joins.