title: Is it better do to a union in SQL or separate queries and then use php array_merge?
body: <p>I have a SQL query that has 4 UNIONS and 4 LEFT JOINS. It is layed out as such:</p>
  
  <pre><code>SELECT ... FROM table1
      LEFT JOIN other_table1
  UNION SELECT ... FROM table2
      LEFT JOIN other_table2
  UNION SELECT ... other_table3
      LEFT JOIN other_table3
  UNION SELECT ... FROM table4
      LEFT JOIN other_table4
  </code></pre>
  
  <p>Would it be better to run 4 separate queries and then merge the results with php after the fact? Or should I keep them together? Which would provide that fastest execution?</p>