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2 posts tagged with "OR优化"

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Outer to Inner Join Conversion

· 6 min read
PawSQL Team
PawSQL Team
Optimize your SQL Queries by Clicks!

Copyright © 2024 PawSQL

Types of Joins​

The types of SQL joins mainly include inner join, outer join (left outer join, right outer join, full outer join), and cross join. C.L. Moffatt explains them very nicely in his article Visual Representation of SQL Joins in a visual way. You will find the information you need in following diagram he presented in his article.

How does Join Type affect Query Execution​

When OR Just Won't Do: Using UNION for Higher SQL Performance

· 4 min read
PawSQL Team
PawSQL Team
Optimize your SQL Queries by Clicks!

Copyright © 2024 PawSQL

Problem Definition​

If two query conditions are connected by OR, the database optimizer may not be able to use indexes to execute the query. For example, for the following SQL statement:

select * from customer where c_phone like '139%' or c_name = 'Ray'

Even if both fields have indexes, they can be rewritten as a UNION query to leverage the indexes and improve query performance: