I have a application in Zoho creator which consist of three form -- Market , TV Station , Census

Market form  has two field  : 

Market Name ;

Market_id  ;

Census form has three field below: 

Market Name ( look up from Market form) , 

Market_id ( lookup from Market form) 

Households Value .

TV Station Form : This form has three fields below

TV station Name

Market  (lookup from Market Form)

Households 

What I need to do is when user select Market from drop down then a script will run and fill the corresponding Households value from census form 

I have tried with below code but not working 

if (input.Market_Name  !=  null)

{

    dat  =  Census [ID == input.Market_Name];

    input.Households = dat.Households_Value;

}  

please help me how to do that ?