code: public UpdateBuilder<T, ID> updateColumnExpression(String columnName, String expression) throws SQLException {
  		FieldType fieldType = verifyColumnName(columnName);
  		if (fieldType.isForeignCollection()) {
  			throw new SQLException("Can't update foreign colletion field: " + columnName);
  		}
  		addUpdateColumnToList(columnName, new SetExpression(columnName, fieldType, expression));
  		return this;
  	}
docs: Add a column to be set to a value for UPDATE statements. This will generate something like 'columnName =
  expression' where the expression is built by the caller.
  
  <p>
  The expression should have any strings escaped using the {@link #escapeValue(String)} or
  {@link #escapeValue(StringBuilder, String)} methods and should have any column names escaped using the
  {@link #escapeColumnName(String)} or {@link #escapeColumnName(StringBuilder, String)} methods.
  </p>