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Preface
For relational databases (Oracle, MySQL), indexing is a way to improve SQL execution efficiency. Reasonable creation of indexes can greatly improve query speed. We often encounter some slow SQL at work. For this For sql, we need to use the execution plan to analyze why this sql is so slow. Next, let's explore the charm of indexes together.
1. What is an index?
- Indexes are data objects used to speed up data access. Proper use of indexes can greatly reduce the number of I/Os, thereby improving data access performance. The index form is similar to a tree. The nodes of the tree store the physical address of each record, which is a pseudo column (ROWID). A normal index will first find the physical address based on the index tree, and then based on the physical address.