Question

I’m attempting to perform a full outer join on two tables that are not related. Each table has a location_id which will eventually form the primary/foreign key relationship (once I figure out this performance issue). When executing the outer join, it just clocks away. Queries and triggers performed against each table on its own complete in less than a second.

This table has 21000 records:

CREATE TABLE [dbo].[TBL_LOCATIONS](
    [OBJECTID] [int] NOT NULL,
    [Loc_Name] [nvarchar](100) NULL,
    [Location_ID] [uniqueidentifier] NULL,
    [SHAPE] [geometry] NULL,

 CONSTRAINT [R33_pk] PRIMARY KEY CLUSTERED 
(
    [OBJECTID] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON, FILLFACTOR = 75) ON [PRIMARY]
) ON [PRIMARY]
GO
ALTER TABLE [dbo].[TBL_LOCATIONS]  WITH CHECK ADD  CONSTRAINT [g17_ck] CHECK  (([SHAPE].[STSrid]=(26917)))
GO
ALTER TABLE [dbo].[TBL_LOCATIONS] ADD  CONSTRAINT [DF_TBL_LOCATIONS_Location_ID]  DEFAULT (newsequentialid()) FOR [Location_ID]
GO

CREATE SPATIAL INDEX [S17_idx] ON [dbo].[TBL_LOCATIONS] 
(
    [SHAPE]
)USING  GEOMETRY_GRID 
WITH (
BOUNDING_BOX =(224827, 3923750, 323464, 3967780), GRIDS =(LEVEL_1 = HIGH,LEVEL_2 = HIGH,LEVEL_3 = HIGH,LEVEL_4 = HIGH), 
CELLS_PER_OBJECT = 16, PAD_INDEX  = OFF, SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
GO

CREATE UNIQUE NONCLUSTERED INDEX [UUID_OID_33] ON [dbo].[TBL_LOCATIONS] 
(
    [Location_ID] ASC,
    [OBJECTID] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON, FILLFACTOR = 75) ON [PRIMARY]
GO

This table has 53000 records

CREATE TABLE [dbo].[TBL_EVENTS](
    [OBJECTID] [int] NOT NULL,
    [Event_ID] [uniqueidentifier] NULL,
    [Location_ID] [uniqueidentifier] NULL,
 CONSTRAINT [PK_TBL_EVENTS] PRIMARY KEY CLUSTERED 
(
    [OBJECTID] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
ALTER TABLE [dbo].[TBL_EVENTS] ADD  CONSTRAINT [DF_TBL_EVENTS_Event_ID]  DEFAULT (newsequentialid()) FOR [Event_ID]
GO
ALTER TABLE [dbo].[TBL_EVENTS] ADD  CONSTRAINT [DF_TBL_EVENTS_Event_ID]  DEFAULT (newsequentialid()) FOR [Event_ID]
GO

CREATE UNIQUE NONCLUSTERED INDEX [R36_SDE_ROWID_UK] ON [dbo].[TBL_EVENTS] 
(
    [OBJECTID] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON, FILLFACTOR = 75) ON [PRIMARY]
GO

And here is the query that is running….and running…1 hour and no results.

SELECT     
    TBL_LOCATIONS.Loc_Name, 
    TBL_LOCATIONS.Location_ID, 
    TBL_LOCATIONS.SHAPE, 
    TBL_EVENTS.Event_ID
FROM         
    TBL_EVENTS 
FULL OUTER JOIN
    TBL_LOCATIONS ON TBL_EVENTS.Location_ID = TBL_LOCATIONS.Location_ID

I’ve tried every permutation of attribute indexes on both tables, rebuilding and reorganizing them, nothing affects the performance. The use of ObjectID as PK is mandated by the application, as is the sequentialGUID. I don’t think those are factors here, as both these tables perform splendidly outside of this query. SQL Server 2008 SP1 64BIT on RAID 10/48 GB RAM.

Answer 1

FULL JOIN works well when data in columns used to links tables are unique.

For rows containing duplicated data FULL JOIN behaves like CROSS JOIN and can cause performace issues.

So probably bottleneck comes from duplicates in LOCATION_ID column.