Wht Statistics Are Updated After SELECT Query?

Hi

My understanding is that whenever any INSERT, DELETE, or UPDATE statements execute that impacts significant amount of rows in a table, its statistics must be automatically updated by SQL Server. But it was surprise to see in the profiler that after INSERT no update statistics event happen. But the moment a SELECT is executed on the table the event 'Auto Stats' is shown up. What is the reason behind this? Why the Auto Stats not happening immediately after the INSERT statement?

Following code can be used to illustrate this (in the profiler select the Auto Stats event under Performance):

IF(SELECT OBJECT_ID('t1')) IS NOT NULL
DROP TABLE t1
GO
CREATE TABLE t1(c1 INT, c2 INT IDENTITY)
INSERT INTO t1 (c1) VALUES(1)
INSERT INTO t1 (c1) VALUES(2)
INSERT INTO t1 (c1) VALUES(3)
CREATE NONCLUSTERED INDEX i1 ON t1(c1)

GO

--Now add 10,000 rows to update so that statistics are updated. Look into the profiler:

SET NOCOUNT ON
GO

DECLARE @n INT
SET @n = 1
WHILE @n <= 10000
BEGIN
INSERT INTO t1 (c1) VALUES(2)
SET @n = @n + 1
END

SET NOCOUNT OFF
GO


--Next runt he following statement. The profiler will now show 'Auto Stats' event

SELECT * FROM t1 WHERE c1 = 2



Regards

Sanjay Singh