select count(*) from tabname where C='0' returns how many rows?select count(*) from tabname where C!='0' returns how many rows?if " C!='0'" contains ton of rows, there is no reason to do index scanThe primary purpose of indexing is to help returning ...
显示全部select count(*) from tabname where C='0' returns how many rows?
select count(*) from tabname where C!='0' returns how many rows?
if " C!='0'" contains ton of rows, there is no reason to do index scan
The primary purpose of indexing is to help returning small portion of data.
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