SQL command replace a word in the products description with Variable word?

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?

Is there some one help me? thanks a lot

It is doing exactly what you told it to do.

I'm not clear what exactly you were hoping it would do differently, nor why you are even asking this question in the first place. MUCH MORE information is needed. What business problem is this supposed to solve?

Sorry, I did not explain very well, and make you confuse, I just want to use sql command to replace some phase of the product's description with the product's name, for example, I want replace each "it" in the product's description with its "product's name", what should I do?