I have two tables. Transaction (ID, TERMINALID) and Terminal (ID, TERMINALID, EXPORT_DATE). The goal is to obtain for each row from Transaction table newest recored from Terminal table. Snowflake is used as a backend.
I have this SQL query:
SELECT tr.ID,
(SELECT te.ID
FROM "Terminal" te
WHERE te.TERMINALID = tr.TERMINALID
ORDER BY te.EXPORT_DATE DESC
LIMIT 1)
FROM "Transaction" tr;
But I get this error:
SQL compilation error: Unsupported subquery type cannot be evaluated
Error disappears if I replace tr.TERMINALID with a specific value. So I can't reference parent table from nested SELECT. Why this is not possible? Query works in MySQL.
I'm afraid Snowflake doesn't support correlated subqueries of this kind.
You can achieve what you want by using FIRST_VALUE
to compute best per-terminalid id :
-- First compute per-terminalid best id
with sub1 as (
select
terminalid,
first_value(id) over (partition by terminalid order by d desc) id
from terminal
),
-- Now, make sure there's only one per terminalid id
sub2 as (
select
terminalid,
any_value(id) id
from sub1
group by terminalid
)
-- Now use that result
select tr.ID, sub2.id
FROM "Transaction" tr
JOIN sub2 ON tr.terminalid = sub2.terminalid
You can run subqueries first to see what they do.
We're working on making our support for subqueries better, and possibly there's a simpler rewrite, but I hope it helps.
SELECT
tr.ID
, (SELECT te.ID
FROM "Terminal" te
WHERE te.TERMINALID = tr.TERMINALID
ORDER BY te.EXPORT_DATE DESC
LIMIT 1
) AS the_id -- <<-- add an alias for the column
FROM "Transaction" tr
;
UPDATE:
length for type varchar cannot exceed 10485760
varchar
(or text
) instead Works here (with quoted identifiers):
CREATE TABLE "Transaction" ("ID" VARCHAR(123), "TERMINALID" VARCHAR(123)) ;
CREATE TABLE "Terminal" ( "ID" VARCHAR(123), "TERMINALID" VARCHAR(123), "EXPORT_DATE" DATE);
SELECT tr."ID"
, (SELECT te."ID"
FROM "Terminal" te
WHERE te."TERMINALID" = tr."TERMINALID"
ORDER BY te."EXPORT_DATE" DESC
LIMIT 1) AS meuk
FROM "Transaction" tr
;
BONUS UPDATE: avoid the scalar subquery and use plain old NOT EXISTS(...)
to obtain the record with the most recent date:
SELECT tr."ID"
, te."ID" AS meuk
FROM "Transaction" tr
JOIN "Terminal" te ON te."TERMINALID" = tr."TERMINALID"
AND NOT EXISTS ( SELECT *
FROM "Terminal" nx
WHERE nx."TERMINALID" = te."TERMINALID"
AND nx."EXPORT_DATE" > te."EXPORT_DATE"
)
;
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