如何在PostgreSQL中将结果分组为布尔值

Question

I have a query which returns

Select bool_val
from .....

The query returns many rows with values of True or False or no rows at all.

I want the query to ALWAYS return True Or False based on condition that if there is one true the result is True otherwise False .

For example: query result:

False
False
True
False

Should return True .

query result:

False
False

Should return False .

query result:

no rows

Should return False since the query is empty.

How can I do that with a query without IFs using PostgreSQL?

Answer 1

You can use a boolean aggregate:

select bool_or(bool_val)
from the_table;

To also get a false when the table contains no rows, use coalesce() (thanks Elad)

select coalesce(bool_or(bool_val), false)
from the_table;

Another - possibly faster - option is:

select exists (select 1 from the_table where bool_val)