title: Equivalent to UNIQUE IDENTIFIER in PostgreSQL
body: <p>I was tryiong to switch from MSSQL to PostgreSQL and hence trying to convert queries to PostgreSQL equivalent. However running PostgreSQL query is giving an error:</p>
  
  <blockquote>
    <p>ERROR:  type "uniqueidentifier" does not exist LINE 3:   ID
    UNIQUEIDENTIFIER DEFAULT UUID_GENERATE_V4()::VARCHAR NO...
                 ^ SQL state: 42704 Character: 38</p>
  </blockquote>
  
  <p><strong>MSSQL</strong></p>
  
  <pre><code>CREATE TABLE [dbo].[ISS_AUDIT]
  (
    [ID] UNIQUEIDENTIFIER DEFAULT NEWID() NOT NULL,
    [GRAPH_ID] [varchar](196)
    PRIMARY KEY(ID)
  );
  </code></pre>
  
  <p><strong>PostgreSQL</strong></p>
  
  <pre><code>CREATE EXTENSION IF NOT EXISTS "uuid-ossp";
  
  CREATE TABLE public.ISS_AUDIT
  (
    ID UNIQUEIDENTIFIER DEFAULT UUID_GENERATE_V4()::VARCHAR NOT NULL,
    GRAPH_ID VARCHAR(196),
    PRIMARY KEY(ID)
  );
  </code></pre>
  
  <p>Am I missing something on <strong>UNIQUEIDENTIFIER</strong>  ?</p>