title: MYSQL - Count total of rows from multiple tables with same column name
body: <p>I have three tables: a_survey, b_survey and c_survey. Each of these tables have a column_name "user_id". What I want to do is count the actual posted surveys and return that value in a single row. So, if there was found one record with the matching user_id for each of these tables, the count would return 3. </p>
  
  <p>Here's what I've tried:</p>
  
  <pre><code>select count(user_id) AS total_of_surveys 
    FROM a.survey, b.survey, c.survey 
   WHERE user_id = 3;
  </code></pre>
  
  <p>but I'm getting error:</p>
  
  <pre><code>Column 'user_id' in field list is ambiguous
  </code></pre>
  
  <p>Thanks in advance!</p>