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PaulOrch
Starting Member
1 Post |
 Posted - 2007-08-13 : 05:23:02
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| I'm trying understand how the Estimated number of rows is calculated in SQL 2005. The scenario I have is a very simple query joining 2 tables. The first table can vary in size from < 10 to potentially millions although a few 100,000 is probably common. The other table is huge (500m). The query plan being generated can vary but most of the time it trying to do a nested loop join. The query plan is correctly calculating the estimated rows for the first table, but seems to be massively underestmating this for the second table. If I limit the search to 1 day they should be approx 16m rows in the large table for that day but then estimate number of rows is 100 using a certain non unique, non clustered index. Is there a simple way of being able to calculate this number based on the stats? If I force it to use the PK index it gets closer to the 16m. |
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ashley.sql
Constraint Violating Yak Guru
299 Posts |
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Estimated Number of Rows