Oracle explain execution plan

I. Execution Plan Tree Structure

When an execution plan is displayed, it is similar to a table. In fact, it is a tree structure. This tree structure not only describes the sequence of SQL engine execution operations, but also the relationship between them. Each node in the tree represents an operation, such as table access, connection, and sorting. There is a parent-child relationship between operations. The specific rules are as follows:

1. The parent has one or more children.

2. The child has only one parent

3. The only node without a parent is the root node.

4. When the execution plan is displayed, the child is indented to the right of the parent.

5. The parent is in front of the child (the parent ID is smaller than the child ID)

As shown in:

Corresponding Tree Structure

Next we will classify and explain various execution plans

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