Question about an explain plan.

Hi,

I got the following explain plan for a query:

Order	Execution Step	Object Name	Object Owner	Est Cost	Est Row
Count	Est Byte Count
7	    [-] Select Statement [CHOOSE]			12	1	102
6	        [-] Nested Loops			12	1	102
3	            [-] Sort (Unique)
2	                [-] Table Access (By Index Rowid)


[ANALYZED]	EMAILLATEST	XXXXXXXX	5	1	20

1	                    [ ] Index (Range Scan)


[ANALYZED]	XPKEMAILLATEST	XXXXXXXX	4	1

5	            [-] Table Access (By Index Rowid)


[ANALYZED]	EMAIL	XXXXXXXX	3	1	82

4	                [ ] Index (Unique Scan)


[ANALYZED]	XPKEMAIL	XXXXXXXX	2	28,940,028

One thing I cannot understand in this plan is that the last step, which is a unique scan of an index, contains a very large number as the estimated row count (28,940,028). Do you know what this number would mean for the unique index scan. My understanding is that a unique index scan would always return a single rowid.

Thank you,

D. Received on Fri Oct 21 2005 - 19:38:05 CDT