@azlnlw ,
As we don't have JavaScript activity in ACS, we will not be able to declare a static variables straight forward at the query level. But based on our requirement, we can use below 2 options:
1) Using Option variable:- We can declare a option variable and use it any where in the workflow.
2) Additional data:- In the Additional tab of Query Activity, We can create an element and declare the value in it. Where ever the value is needed, We can use this custom field.
Regards,
Abhishek