title: Convert ARRAY<STRUCT> to multiple columns in BigQuery SQL
body: <p>I'm trying to convert Array&lt; struct > to multiple columns.
  The data structure looks like:</p>
  
  <pre><code>column name: Parameter
  [
    -{
        key: "Publisher_name"
        value: "Rubicon"
     }
    -{
        key: "device_type"
        value: "IDFA"
     }
    -{
        key: "device_id"
        value: "AAAA-BBBB-CCCC-DDDD"
     }
  ] 
  </code></pre>
  
  <p>What I want to get:</p>
  
  <pre><code>publisher_name  device_type  device_id
  Rubicon         IDFA         AAAA-BBBB-CCCC-DDDD
  </code></pre>
  
  <p>I have tried this which  caused the duplicates of other columns.</p>
  
  <pre><code>select h from table unnest(parameter) as h
  </code></pre>
  
  <p>BTW, I am very curious why do we want to use this kind of structure in Bigquery. Can't we just add the above 3 columns into table?</p>