How to use 'exist' for multiple values in postgres?

Question

I have been trying to figure out how I can combine multiple values to see if one of them returns True then it exists. Meaning that if A is True and B is False = Return True. If both are False then of course we return = False.

What I have currently done is:

dict_tuple = {"type": "fruit", "link": link, "store": store}

sql_query = "SELECT store, link FROM public.fruit_urls WHERE link_type=%(type)s AND link=%(link)s AND store=%(store)s union SELECT store, link FROM public.store_items WHERE link=%(link)s AND store=%(store)s"

which seems to work but I would like to convert the query to use exists instead since I do check if its in the database or not.

I managed to solve to do one check:

sql_query = "SELECT EXISTS (SELECT store, link FROM public.store_items WHERE link=%(link)s AND store=%(store)s)"

but how can I combine both

"SELECT EXISTS (SELECT store, link FROM public.store_items WHERE link=%(link)s AND store=%(store)s)"
"SELECT store, link FROM public.manual_urls WHERE link_type=%(type)s AND link=%(link)s AND store=%(store)s"

together and then return if one of them are in the database or not

Simply put select exists(...) around your initial UNION query. — Vadim Landa
– Vadim Landa, Commented Apr 8, 2021 at 13:41
Do you mean like this? SELECT EXISTS ("SELECT store, link FROM public.fruit_urls WHERE link_type=%(type)s AND link=%(link)s AND store=%(store)s union SELECT store, link FROM public.store_items WHERE link=%(link)s AND store=%(store)s") ? @VadimLanda — PythonNewbie
– PythonNewbie, Commented Apr 8, 2021 at 13:43
Oh... That was as easy as that. I did not know that :) @VadimLanda - If you want, you could do that as an answer and Iwill mark it as the solution :) — PythonNewbie
– PythonNewbie, Commented Apr 8, 2021 at 14:07

Vadim Landa · Accepted Answer · 2021-04-08 14:21:33Z

1

Just surround SELECT ... UNION SELECT... with SELECT EXISTS(...):

SELECT EXISTS (
  SELECT store, link FROM public.fruit_urls WHERE link_type=%(type)s AND link=%(link)s AND store=%(store)s 
  UNION 
  SELECT store, link FROM public.store_items WHERE link=%(link)s AND store=%(store)s)

answered Apr 8, 2021 at 14:21

Vadim Landa

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