I want to use SQL command to find and replace a word in the products description, and I want to replace with Variable word, such as replace some word with the exactly product's name, I use this command:

update products_description set products_description=replace(products_description,'xxx','$meta_products_name');

but it did not work at all, it just replace all xxx with $meta_products_name, can not get the product's name and replace xxx, anyone can help me?