title: Clickhouse how to merge table with different columns?
body: <p>Say I have 2 tables.</p>
  <pre><code>CREATE TABLE IF NOT EXISTS table_1
  (
  key1 FixedString(10),
  dt Datetime,
  
  data1 Float32 default nan,
  data2 Float32 default nan
  )
  Engine = MergeTree()
  order by (key1,dt);
  
  CREATE TABLE IF NOT EXISTS table_2
  (
  key1 FixedString(10),
  dt Datetime,
  
  data3 Float32 default nan,
  data4 Float32 default nan
  )
  Engine = MergeTree()
  order by (key1,dt);
  </code></pre>
  <p>After a while, I realized that it's better to manage data1,data2,data3,data4 in one table, ie. I need a table like this</p>
  <pre><code>CREATE TABLE IF NOT EXISTS table_3
  (
  key1 FixedString(10),
  dt Datetime,
  
  data1 Float32 default nan,
  data2 Float32 default nan,
  data3 Float32 default nan,
  data4 Float32 default nan
  )
  Engine = MergeTree()
  order by (key1,dt);
  </code></pre>
  <p>Since Clickkhouse does not support update...select, I can't find a way to merge table_1 and table_2 into table_3. This can't be done from the python side either, since clickhouse-driver does not support &quot;update&quot;.</p>
  <p>Please help!</p>