SQL Server Statistics

What statistics are for?

Query processing phases

• Bullet One
• Bullet Two
• good enough execution plan

Cardinality estimation

• number of rows that need to be processed on each step of the query execution
• important factor in query optimization
• affects:
  • choice of join strategies
  • memory grants

What statistics are?

• system object
• contain the information about data distribution:
  • in columns which comprise indices' keys
  • sometimes in regular column values
• column data type has to support comparison operators

DBCC SHOW_STATISTICS

• returns three result sets
  1. general metadata information
  2. density
  3. histogram
• Bullet Two
• Bullet Three