# 3.1.Obtain Query Execution Plan
## 1. Introduction
* In SQL server, we can get some useful information to help us to optimize efficiency of our SQL query from **Query Execution Plan**,
such as: Why is this query running slow? Is my index getting used? Why isn’t my index getting used? Why does this query run faster than this query?
## 2.Types Query Execution Plan
* 1.Estimated execution plan
* the plan that represents **the output from the optimizer**
* 2.Actual execution plan
* the plan that represents the output from the actual query execution
## 3.Get started
* 1.Push **Include Actual Execution Plan** button or **Ctrl + M** before execute SQL query 
* Or push **Display Estimated Execution Plan** button or **Ctrl + L** before execute SQL query 
* 2.Execute SQL query by push **F5**
* 3.After SQL query finished, we can obtain a report below
## 4.ToolTips
* 1.SELECT operator
* (1) Cached plan size (記憶體大小)
* \[cache performance issues]: how much memory the plan generated by this query will take up in stored procedure cache.
* (2) Estimated Operator Cost
* (3) Estimated Subtree Cost (累積至目前的accumulated optimizer cost大小)
* tells us the accumulated optimizer cost assigned to this step and all previous steps, but remember to read from right to left
* (4) Estimated number of rows
* 2.Table Scan
* (1) Estimated Operator Cost/ Estimated Subtree Cost
* the **operator cost** and the **subtree cost** are the same, since the table scan is the only operator. (如果有多個operator, 每一個operator個別的cost將會加總到total)
* (2) Estimated number of rows
* Change as various operators perform their work on the data as it passes between each operator (不同的operator, Estimated number of rows也會不同)
* (3) Ordered
* whether or not the data that this operator is working with is in an ordered state.(此operator是否會使data呈現排序狀態, 是否是ordered可以讓我們知道哪裡可能有多餘的處理, 以讓data進入排序狀態, 像是order by)
## 5.Operator Properties
* Properties has more information than Tool Tip
* Follow steps bellow:
* 1.Right click Table Scan and select Property
* 2.Check the table on the right side:
* Defined Values
* Estimated Rebinds /Estimated Rewinds
* The number of times an Init() operator is called in the plan
* Forced Index
* NoExpandHint
* Object
* Output List property
## 6.Reference
*
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