{
    head:{
        type:"APACHE_DRILL_PHYSICAL",
        version:"1",
        generator:{
            type:"manual"
        }
    },
    graph:[
        {
            @id:1,
            pop:"mock-sub-scan",
            url: "http://apache.org",
            entries:[
                {records: 1, types: [
                  {name: "varcharcol", type: "VARCHAR", mode: "REQUIRED"},
                  {name: "nullvarcharcol", type: "VARCHAR", mode: "OPTIONAL"}
                ]}
            ]
        },
        {
            @id:2,
            child: 1,
            pop:"project",
            exprs: [
              { ref: "col1", expr: "concat('abc', 'ABC')"},
              { ref: "col2", expr: "concat('abc', '')"},
              { ref: "col3", expr: "concat('', 'ABC')"},
              { ref: "col4", expr: "concat('', '')"}
           ]
        },
        {
            @id: 3,
            child: 2,
            pop: "screen"
        }
    ]
}