How To Rebuild Indexes with ALTER INDEX ... REBUILD in SQL Server?

When an index is defragmented to a large percentage, like > 30%, you can use the "ALTER INDEX ... REBUILD" statement to rebuild the index. Here is a tutorial exercise on rebuilding indexes:

USE FyiCenterData;
GO

UPDATE fyi_links_indexed SET url = REVERSE(url)
   WHERE id <=50000;
GO
(50000 row(s) affected)

SELECT i.index_id, i.name, s.avg_fragmentation_in_percent
   FROM sys.dm_db_index_physical_stats (
      DB_ID(N'FyiCenterData'), 
      OBJECT_ID(N'fyi_links_indexed'),
      DEFAULT, DEFAULT, DEFAULT) s, sys.indexes i
   WHERE s.object_id = i.object_id
      AND s.index_id = i.index_id;
GO
0        NULL             0.574712643678161
2        fyi_links_url    85.0142045454545
3        fyi_links_counts 0.448430493273543

ALTER INDEX fyi_links_url ON fyi_links_indexed REBUILD;
GO

SELECT i.index_id, i.name, s.avg_fragmentation_in_percent
   FROM sys.dm_db_index_physical_stats (
      DB_ID(N'FyiCenterData'), 
      OBJECT_ID(N'fyi_links_indexed'),
      DEFAULT, DEFAULT, DEFAULT) s, sys.indexes i
   WHERE s.object_id = i.object_id
      AND s.index_id = i.index_id;
GO
0        NULL             0.574712643678161
2        fyi_links_url    0
3        fyi_links_counts 0.448430493273543

Rebuilding an index brings the fragmentation level to 0% in this case.

⇒Understanding and Managing Indexes in SQL Server

⇒⇒SQL Server Database Tutorials