SQL syntax: I am working with mySQL. How do I write a SQL statement
which updates a table as follows:

- In table "Table_X",
- For field "Field_Y", which is of type char(64),
- For each record that contains one or more instances of the string
"ab" in "Field_Y",
- Replace "ab" with "cde" for all instances of "ab".

MySQL 4.1 has nice function called REPLACE - most engines do not have such a thing.

http://dev.mysql.com/doc/mysql/en/string-functions.html

For your example:

update Table_X set Field_Y = replace(Field_Y, 'ab', 'cde' );

The double reference to Field_Y is allowed.