title: Why spark's global_temp database not visible?
body: <p>With the new <code>createGlobalTempView</code> in Spark 2.1.0, it is possible to share a table amongst multiple spark sessions</p>
  
  <p>However, this database can't be accessible from the outside. For example :</p>
  
  <pre><code>scala&gt; spark.sql("select * from global_temp.salaries")
  res240: org.apache.spark.sql.DataFrame = [yearID: string, teamID: string ... 3 more fields]
  
  scala&gt; salaries.createGlobalTempView("salaries")
  
  scala&gt; spark.sql("select * from global_temp.salaries").show(5)
  +------+------+----+---------+------+
  |yearID|teamID|lgID| playerID|salary|
  +------+------+----+---------+------+
  |  1985|   ATL|  NL|barkele01|870000|
  |  1985|   ATL|  NL|bedrost01|550000|
  |  1985|   ATL|  NL|benedbr01|545000|
  |  1985|   ATL|  NL| campri01|633333|
  |  1985|   ATL|  NL|ceronri01|625000|
  +------+------+----+---------+------+
  only showing top 5 rows
  </code></pre>
  
  <p>Nothing is wrong here, but here comes the strange behaviour</p>
  
  <pre><code>scala&gt; spark.catalog.listTables.show
  +----+--------+-----------+---------+-----------+
  |name|database|description|tableType|isTemporary|
  +----+--------+-----------+---------+-----------+
  +----+--------+-----------+---------+-----------+
  
  scala&gt; spark.catalog.tableExists("global_temp","salaries")
  res249: Boolean = true
  </code></pre>
  
  <p>My guess is that <code>global_temp</code> database is hidden for all users, but it is possible to query tables on it if we already know wich table to query. </p>
  
  <p>Is it a normal behaviour or am I doing something wrong ?</p>
  
  <p>Thanks for any explanaitions</p>