title: PSQL join - Column "table.column" does not exist
body: <p>I need to update records in a table but only if a certain column of this table equals the content of a column of another table. <br><br>
  But first, just to be sure, I want to select all of the records that meets this specific so I've tried something like: <br></p>
  
  <pre><code>SELECT * FROM "table1" as ARR INNER JOIN "table2" as AOP ON ("AOP.col2" = "ARR.col1");
  </code></pre>
  
  <p>But the query returns this error: <br></p>
  
  <blockquote>
    <p>ERROR:  column "AOP.col2" does not exist<br>
    LINE 1: ...as ARR INNER JOIN "table2" as AOP ON ("AOP.col...</p>
  </blockquote>
  
  <p>What am I doing wrong? (obviously the column does exist) <br>
  Seeing this error do you think the following update query will also fail? <br></p>
  
  <pre><code>UPDATE "table2" AS AOP
  SET "col2" = "ARR.col1"
  FROM "table1" AS ARR
  WHERE "AOP.col3" = "ARR.col4";
  </code></pre>