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How to write SQL to effectively use composite index?
2022-02-04 16:37:20 【Alibaba cloud Q & A】
How to write sql Can effectively use the composite index ？
Take the answer 1：
Composite index , It's also called composite index , Users can index multiple columns , This index is called a composite index .
When we create a composite index , Such as (k1,k2,k3), It's equivalent to creating （k1）、(k1,k2) and (k1,k2,k3) Three indexes , This is the left most matching principle .
select * from table where k1=A AND k2=B AND k3=D
About Composite Index , We need to focus on queries Sql The order of conditions , Ensure that the leftmost matching principle is effective , At the same time, unnecessary redundant indexes can be deleted .
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