title: Change TEXT column default from null to '' (empty string)
body: <p>I have a table where default value is not specified at the time of table creation. 
  Now I want to change default value to '' (empty string).
  When I run alter table query it get success but still on new row insertion table consider NULL as default value if column value is not specified.</p>
  
  <p>TABLE Schema::</p>
  
  <pre><code>CREATE TABLE `table1` (
    `col1` INT(11) NOT NULL AUTO_INCREMENT,
    `col2` TEXT,
    `col3` INT(11) DEFAULT NULL,
    `col4` TINYINT(1) DEFAULT '0',
    PRIMARY KEY (`id`)
  );
  </code></pre>
  
  <p>ALTER Query::</p>
  
  <pre><code>ALTER TABLE `table1` change `col2` `col2` text  default '';
  </code></pre>