Using "SELECT IF" winth another dataset

Question

I'm trying to do this query in BigQuery.

I have a Table1, and a Table 2. I'd like to do something like this:

If (select Table 2 with specific criteria) returns > 0 records,

   then perform this select on table 1 (select one), 

Otherwise, perform another select on table 1 (select 2).

I can do something like:

SELECT IF (1=1,"YES", "NO"), but, when I replace 1=1 with my select, like this:

SELECT IF ((SELECT count(*) FROM Table1)>0,"YES", "NO")

is not working anymore...

Any help??? I hope any expert can help me!

best regards,

Albert

Answer 1

You can't have nested select statement like that. What needs to happen is your inner select has to be a subquery and aliased something like:

SELECT 
    IF(inner_table.count_column > 0, "YES", "NO)  -- here we select the 'count_column' from 'inner_table
FROM   
(   
    (SELECT count(*) as count_column FROM table1) 
) as inner_table -- aliasing the inner select as 'inner_table'

Hope this makes sense. Pretty much this is how it works with bigquery, you need to construct your nested statements into subqueries. Here's some reading https://developers.google.com/bigquery/query-reference#from