将两个 SQL 查询合并为同一张表的一个查询

Question

I have a table called COMPUTED_DATA . It contains 3 columns: data, cluster, and last_execution.

There is job which runs every 2 weeks which inserts multiple data for a cluster and its last_execution time.

My requirement is to get the data for a cluster for its most recent last_execution time. Currently I have written query like this in my code

last_execution = SELECT distinct(last_execution) FROM COMPUTED_DATA 
WHERE cluster=1204 AND ORDER BY last_execution DESC limit 1

The above query gets me the most recent last_execution

data = SELECT data FROM COMPUTED_DATA WHERE cluster=1204 AND
last_execution={last_execution}

This query uses that last_execution to get the data.

My question is can this be combined into just 1 query. I am running this in my spark cluster so each SQL query is very time expensive. Hence I want to combine this into one query. Please help.

EDIT: the second query where I am getting data from returns multiple rows. Hence I cannot use limit on the second query because that count is unknown.

Answer 1

Yes it can

SELECT
  data
FROM
  COMPUTED_DATA
WHERE
  cluster = 1204 and last_execution=(SELECT distinct(last_execution) FROM COMPUTED_DATA 
WHERE cluster=1204 AND ORDER BY last_execution DESC limit 1)

This isn't the most beautiful way to write this, but you get idea how to use subquery in where clause.