Difference between Mirin and cooking alcohol

I always assumed that みりん is 料理酒 (cooking alcohol?) but today I saw a recipe that requires both. What is the difference between these 2 ingredients?

From what I understand, mirin is a type of sweet sake, while ryorisake has had salt added to make it undrinkable. So seems they can be used similarly, but will impart different flavors to the finished food.

I checked the contents of mirin by internet.

It contains glucose and several amino acids and organic acids comes from rice.

Also sake contains such contents but small amount.

BTW I will tell you special Teriyaki sauce recipe.

30% mirin, 30% ketchup, 10% soysauce, red wine are mixed and heated to evaporate alcohol.

It will be good for steak.
Try.

Liquid seasonings sold in Japan whose names include "みりん" can be classified under a few categories.
Also the word "料理酒 [りょうりしゅ]" may refer to various liquid seasonings; we don't have a common clear definition of it.

If that recipe is written by a Japanese cooking expert, みりん indicated there probably refers to what is generally called as 本みりん [ほんみりん].

mirin is a type of sweet sake

I agree.
本みりん is a liquid seasoning usually made from rice, rice kōji and shōchū (= rough sprit from sake); starch of the rice is converted into sugar through fermentation.
(Legally in the Liquor Tax Act, 本みりん is prescribed as みりん, and treated as alcohol beverage on which a liquor tax is imposed.)
The amount of Ethanol in 本みりん is around 14 volume percent.
If a bottle of a liquid seasoning sold in Japan has a label where its name (名称) is indicated as みりん, it is 本みりん.

On the other hand, みりん風調味料 is a liquid seasoning manufactured to have a 本みりん-like flavor, usually with no alcoholic liquid added.
(Legally みりん風調味料 is not treated as alcohol beverage.)
The amount of Ethanol in みりん風調味料 is less than 1 volume percent.

料理酒 mostly includes salt and/or acid which is, as yllwsmrf mentions, added to make it undrinkable.
(Legally such undrinkable 料理酒 is not treated as alcohol beverage.)
The amount of Ethanol in 料理酒 may be more than 10 volume percent, depending on products.