UPDATE `table_name`
 SET `field_name` = replace(same_field_name, 'unwanted_text', 'wanted_text')

UPDATE `tj_posts`
SET `post_content` = replace(post_content, 'mysite.com/wordpress', 'mysite.com/news')

// Connect to your MySQL database.
$hostname = "localhost";
$username = "db_username";
$password = "db_password";
$database = "db_name";

mysql_connect($hostname, $username, $password);

// The find and replace strings.
$find = "find_this_text";
$replace = "replace_with_this_text";

$loop = mysql_query("
    SELECT
        concat('UPDATE ',table_schema,'.',table_name, ' SET ',column_name, '=replace(',column_name,', ''{$find}'', ''{$replace}'');') AS s
    FROM
        information_schema.columns
    WHERE
        table_schema = '{$database}'")
or die ('Cant loop through dbfields: ' . mysql_error());

while ($query = mysql_fetch_assoc($loop))
{
        mysql_query($query['s']);
}

mysqldump -u user -p databasename > ./db.sql

sed -i 's/oldString/newString/g' ./db.sql

mysql -u user -p databasename < ./db.sql

UPDATE table SET field = replace(field, text_needs_to_be_replaced, text_required);

UPDATE student SET student_name = replace(student_name, 'John', 'Mark');

UPDATE `wp_posts` AS `toUpdate`,
(SELECT `ID`,REPLACE(`guid`,'http://old.tld','http://new.tld') AS `guid`
 FROM `wp_posts` WHERE `guid` LIKE 'http://old.tld%') AS `updated`
SET `toUpdate`.`guid`=`updated`.`guid`
WHERE `toUpdate`.`ID`=`updated`.`ID`;

SELECT `toUpdate`.`guid` AS `old guid`,`updated`.`guid` AS `new guid`
FROM `wp_posts` AS `toUpdate`,
(SELECT `ID`,REPLACE(`guid`,'http://old.tld','http://new.tld') AS `guid`
 FROM `wp_posts` WHERE `guid` LIKE 'http://old.tld%') AS `updated`
WHERE `toUpdate`.`ID`=`updated`.`ID`;

update TABLE_NAME set FIELD_NAME =
 replace(FIELD_NAME, 'Text to find', 'text to replace with');