Postdata allows you to pass variables in the query to fetch data dynamically. To demonstrate the use of variables let’s write a query to get the Ninja whose id is 61bd1dbc918f12c17b9c6483.

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Variables

Go to the variables section and define the variable. 
{
  "id": "61bd1dbc918f12c17b9c6483"
}

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Using the variable in the query

Now create a query getCharacter with variables as shown below: 
 query getCharacter($id:String!){
  character(id:$id) {
    name
    avatarSrc
    rank
    description
    village
  }
}
Postdata will retrieve the value of the variable and execute the query to get the below response. 
{
  "data": {
    "character": {
      "name": "Aburame Shibi",
      "avatarSrc": "https://narutoql.s3.amazonaws.com/Aburame2.jpg",
      "rank": "Jounin",
      "description": "Aburame Shibi is the father of Aburame Shino. Like his son, his body is also inhabited by the destruction bugs.",
      "village": "leaf village"
    }
  }
}