title: Liquibase - Add defaultValueComputed as CURRENT_TIMESTAMP to timestamp column
body: <p>I am using liquibase 3.5.3 to run <code>liquibase update</code> command on MySql 5.5. I have below <code>changeSet</code> to create a table which has a column as <code>Created_Time</code> that should have a default value as <code>CURRENT_TIMESTAMP</code>.</p>
  
  <pre><code>&lt;changeSet author="authorName" id="AutoGeneratedId"&gt;
      &lt;createTable tableName="aTable"&gt;
          &lt;column autoIncrement="true" name="Id" type="INT"&gt;
              &lt;constraints primaryKey="true"/&gt;
          &lt;/column&gt;
          &lt;column name="Code" type="VARCHAR(45)"/&gt;
          &lt;column defaultValueComputed="CURRENT_TIMESTAMP" name="Created_Time" type="TIMESTAMP(19)"/&gt;
      &lt;/createTable&gt;
  &lt;/changeSet&gt;
  </code></pre>
  
  <p>While firing liquibase command it throws an exception as 
  <code>Unexpected error running Liquibase: Invalid default value for 'Created_Time' [Failed SQL: CREATE TABLE aTable (Id INT AUTO_INCREMENT NOT NULL, Code VARCHAR(45) NULL, Created_Time TIMESTAMP(19) DEFAULT NOW() NULL, CONSTRAINT PK_ATABLE PRIMARY KEY (Id))]</code></p>
  
  <p>Liquibase is converting <code>CURRENT_TIMESTAMP</code> into <code>NOW()</code> that might be causing this issue.</p>
  
  <p>Can some please provide me any solution or alternative to this issue?</p>