The core building blocks of an Execution Plan are
- Clustered Index Scan
- and SELECT.
Operators are the smallest unit of work to execute a query. SQL Server breaks the query down into multiple steps and goes through all the steps one by one in order to execute the query.
Operators in an execution plan contain information about what SQL Server has done at that step. Possible values can range from reading a table or index, to merging data from two tables.
Here comes a couple of icons of operators in Execution Plans.
Since SQL Server breaks the query execution into steps of execution (operators), there should be a mechanism to transition between the steps and pass data from one step to another. Within an execution plan, Arrows are the mechanism to transition the execution from one step to another.
Apart from execution transition, Arrows serve other goals. They are also used to represent the data that each operator has passed to the next operator. In other words, every operator in an execution plan does whatever it is supposed to do, and passes the result data to the next operator; Arrows are used to represent the data flow.