How to sum several rows by id MySql [duplicate]

This question already has an answer here:

• MySQL Group by SUM 2 answers
• Laravel Eloquent: sum with groupBy 1 answer

This should be easy, but I can't figure it out. I have a product table which looks like this (very abbreviated for clarity)

[![product_quantity][1]][1]

So all I want to do is to aggragate the quantities for each product id eg product id 128 quantity of 37. All I have come up with is the following, which groups product_name but does not add the quantities correctly. This is Laravel Query builder code. But no matter, raw SQL is fine if you can help. Thank You !

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