First, let's look at the variables inside the package.
There are two kinds of SSIS package variables, one is the built-in variable of the system, and it is the beginning of the SSIS package, which is the user-defined variables.
In SSIS packages, the types of commonly used variables include the following: Int32,string,boolean,datetime,object ...
Two, let's take a look at the constraints inside the package (line)
As the line shown in the figure is a constraint, the official explanation is that precedence constrains the executable files, containers, and tasks in the package in the control flow, and specifies the conditions that determine whether the executable file is running. The expression in the diagram is that the "Insert Table variable" Step is executed when the "Get variable Value" step succeeds and satisfies the condition in the precedence constraint.