"Statistics, Fragmentation, and the Cost of Writes"

1. What is the primary reason statistics are critical for query performance?

They determine the execution plan. They ensure data security. They reduce the size of the database. They limit the number of queries executed.

2. Under what condition does SQL Server update statistics automatically for a large table with compatibility level 120 or below?

When 500 rows plus 10% of the table change. When 100 rows change. When 500 rows change plus 20% of the rows. When 1000 rows are modified.

3. What is the recommended action when the average fragmentation in an index exceeds 30%?

Ignore it and check later. Reorganize if possible, otherwise rebuild. Rebuild it immediately without consideration. Disable the index.

4. When should you consider updating statistics with FULLSCAN?

For small tables only. When tuning queries on skewed distributions. Only if the modification counter is high. Daily without exception.