如何在子查询中使用LIMIT 1

Question

I'm trying to run an update querywith a table that joins on itself and I want to assign the column M_USER to the first row that the select statement is returning. I know in SQL Server, I could use TOP 1 and i think the equivalent would be LIMIT 1 in Vertica.

So I tried to write the query with the LIMIT 1 but i'm getting this error:

ERROR: Correlated subquery expression without aggregates and with limit is not supported

Here's my query:

UPDATE REPORT.sub_2019 a
SET M_USER= (Select u.UPDATED_USER 
        from REPORT.sub_2019 u 
        where u.MBR_ID = a.MBR_ID 
        and u.NAME= a.NAME and u.STATUS_REASON = 'Pending' limit 1)
where a.RESULT is not null

I just want to grab the first UPDATED_USER that the subquery is returning. Should I use LIMIT or any other way of writing the query?

Answer 1

I think you could use the rank function for this:

UPDATE REPORT.sub_2019 a
SET M_USER= (Select u.UPDATED_USER, rank() OVER (PARTITION BY <field> ORDER BY <field> DESC) as rank 
        from REPORT.sub_2019 u 
        where u.MBR_ID = a.MBR_ID 
        and u.NAME= a.NAME 
        and u.STATUS_REASON = 'Pending'
        and rank = 1)
where a.RESULT is not null

Answer 2

Use max or min in subquery

UPDATE REPORT.sub_2019 a
SET M_USER= (Select min(u.UPDATED_USER )
        from REPORT.sub_2019 u 
        where u.MBR_ID = a.MBR_ID 
        and u.NAME= a.NAME and u.STATUS_REASON = 'Pending')
where a.RESULT is not null