SQL Server logical read, pre-read, and physical read

　DBCC Dropcleanbuffers    -- empty cache SETSTATISTICSon    --  Turn on IO statistics SELECT* from person    -- query statement　　　　

1. Pre-read: Use the estimated information to go to the hard disk to read the data to the cache. Pre-read 100 times, which is estimated to read 100 pages of data from the hard disk to the cache.
2. Physical reads: After the query plan is generated, if the cache is missing the required data, let the cache read the hard disk again. Physically read 10 pages and read 10 pages of data from the hard disk to the cache.
3. Logical read: All data is fetched from the cache. Read Logic 100 times, which means fetching 100 pages of data from the cache.