How can I import a JSON file into PostgreSQL?

You can feed the JSON into a SQL statement that extracts the information and inserts that into the table. If the JSON attributes have exactly the name as the table columns you can do something like this:

<span class="kwd">with</span><span class="pln"> customer_json </span><span class="pun">(</span><span class="pln">doc</span><span class="pun">)</span> <span class="kwd">as</span> <span class="pun">(</span>
   <span class="kwd">values</span> 
    <span class="pun">(</span><span class="str">'[
      {
        "id": 23635,
        "name": "Jerry Green",
        "comment": "Imported from facebook."
      },
      {
        "id": 23636,
        "name": "John Wayne",
        "comment": "Imported from facebook."
      }
    ]'</span><span class="pun">::</span><span class="pln">json</span><span class="pun">)</span>
<span class="pun">)</span>
<span class="kwd">insert</span> <span class="kwd">into</span><span class="pln"> customer </span><span class="pun">(</span><span class="pln">id</span><span class="pun">,</span><span class="pln"> name</span><span class="pun">,</span><span class="pln"> comment</span><span class="pun">)</span>
<span class="kwd">select</span><span class="pln"> p</span><span class="pun">.*</span>
<span class="kwd">from</span><span class="pln"> customer_json l
  </span><span class="kwd">cross</span> <span class="kwd">join</span><span class="pln"> lateral json_populate_recordset</span><span class="pun">(</span><span class="kwd">null</span><span class="pun">::</span><span class="pln">customer</span><span class="pun">,</span><span class="pln"> doc</span><span class="pun">)</span> <span class="kwd">as</span><span class="pln"> p
</span><span class="kwd">on</span><span class="pln"> conflict </span><span class="pun">(</span><span class="pln">id</span><span class="pun">)</span><span class="pln"> do </span><span class="kwd">update</span> 
  <span class="kwd">set</span><span class="pln"> name </span><span class="pun">=</span><span class="pln"> excluded</span><span class="pun">.</span><span class="pln">name</span><span class="pun">,</span><span class="pln"> 
      comment </span><span class="pun">=</span><span class="pln"> excluded</span><span class="pun">.</span><span class="pln">comment</span><span class="pun">;</span>

New customers will be inserted, existing ones will be updated. The “magic” part is the <span style="color: #242729;">json_populate_recordset(null::customer, doc)</span> which generates a relational representation of the JSON objects.