title: String to date time conversion Bigquery
body: <p>I have a source table which has dates stored in string format as below:</p>
  
  <pre><code>1984-10-28 00:00:00
  1988-11-22 00:00:00 
  1990-01-08 00:00:00
  1983-06-22 00:00:00 
  </code></pre>
  
  <p>Then created a table test1 as below:</p>
  
  <pre><code>mk -t xyz.test birthdate:timestamp
  </code></pre>
  
  <p>When I write a query to convert all the dates from source table to timestamp and save it to test1 it gives an error:</p>
  
  <pre><code>SELECT FORMAT_UTC_USEC(birthdate) AS birthdate FROM [sourcetable] LIMIT 10
  
  Error: Invalid schema update. Field birthdate has changed type
  Job ID: [Project]:job_5P4gFVl4wiYuyXL0vY5VZNtCZOU
  </code></pre>
  
  <p>Please help if I am doing anything wrong</p>