title: When creating a column using liquibase, how do I specify a value for that column based on an existing column?
body: <p>I have an existing mysql table with two columns a and b.  </p>
  
  <p>I now want to add a column c to that table. </p>
  
  <p>c should be nullable, should have a default value of NULL, except in those rows where column b has the value 10. Where b has the value 10, c should have a value X.</p>
  
  <p>I understand that it is fairly simple to do this using SQL, but I want to do this using liquibase, since liquibase is what we use for our schema migrations.</p>