sql-logical-optimization.md

title
SQL Logical Optimization

SQL Logical Optimization

This chapter explains some key logic rewrites to help you understand how TiDB generates the final query plan. For example, when you execute the select * from t where t.a in (select t1.a from t1 where t1.b=t.b) query in TiDB, you will find that the IN sub-query t.a in (select t1.a from t1 where t1.b=t.b) does not exist because TiDB has made some rewrites here.

This chapter introduces the following key rewrites:

• Subquery Related Optimizations
• Column Pruning
• Decorrelation of Correlated Subquery
• Eliminate Max/Min
• Predicates Push Down
• Partition Pruning
• TopN and Limit Operator Push Down
• Join Reorder