Can you have if-then-else logic in SQL? [duplicate

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How do I perform an IF…THEN in an SQL SELECT? (27 answers)

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I need to do select data from a table based on some kind of priority like so:

select product, price from table1 where project = 1

-- pseudo: if no price found, do this:
select product, price from table1 where customer = 2

-- pseudo: if still no price found, do this:
select product, price from table1 where company = 3

That is, if I found 3 products with prices based on project = X, I don't want to select on customer = Y. I just want to return the resulting 3 rows and be done.

How are you supposed to do stuff like this in SQL? Use some kind of CASE-statement for the pseudo-if's? Do a union or some other smart thing?

Edit: I'm using MS SQL.

Thanks!

Answer 1

there is a case statement, but i think the below is more accurate/efficient/easier to read for what you want.

select 
  product
  ,coalesce(t4.price,t2.price, t3.price) as price
from table1 t1
left join table1 t2 on t1.product = t2.product and t2.customer =2
left join table1 t3 on t1.product = t3.product and t3.company =3
left join table1 t4 on t1.product = t4.product and t4.project =1