Netezza - update one table with max data from another table - sql

Question

I have a table in netezza that I need to update. The columns I am working with are
TABLE A
ID_NO
ENTRY_DATE
PRICE
TABLE B
ID_NO
START_DATE
END_DATE
PRICE
So an example of the data would look like this:
TABLE A
ID_NO
ENTRY_DATE
PRICE
123
2020-05-01
123
2020-08-15
TABLE B
ID_NO
START_DATE
END_DATE
PRICE
123
2019-01-01
2019-11-01
$7.64
123
2020-04-30
2020-05-02
$6.19
123
2020-04-15
2020-08-30
$2.19
I need to update the PRICE in TABLE A to be the max PRICE from TABLE B where a.ENTRY_DATE is between b.START_DATE and b.END_DATE. So the final table should look like this:
TABLE A
ID_NO
ENTRY_DATE
PRICE
123
2020-05-01
$6.19
123
2020-08-15
$2.19
This is what I have so far, but it just ends up taking the max price that fits either row rather than doing the calculation for each row:
update TABLE_A
set PRICE=(select max(b.PRICE)
from TABLE_B b
inner join TABLE_A a on a.ID_NO=b.ID_NO
where a.ENTRY_DATE between b.START_DATE and b.END_DATE)

Answer 1

I don't have access to Netezza, but a usual format would be to use a correlated sub-query.
That is, instead of including TABLE_A again in the query, you refer to the outer reference to TABLE_A...
update
TABLE_A
set
PRICE = (
select max(b.PRICE)
from TABLE_B b
where TABLE_A.ID_NO = b.ID_NO
and TABLE_A.ENTRY_DATE between b.START_DATE and b.END_DATE
)
In this way, the correlated-sub-query is essentially invoked once for each row in TABLE_A and that invocation uses the current row from TABLE_A as its parameters.
An alternative could be...
update
TABLE_A
set
PRICE = revised.PRICE
from
(
select a.ID_NO, a.ENTRY_DATE, max(b.PRICE) AS PRICE
from TABLE_B b
inner join TABLE_A a on a.ID_NO=b.ID_NO
where a.ENTRY_DATE between b.START_DATE and b.END_DATE
group by a.ID_NO, a.ENTRY_DATE
)
AS revised
where
TABLE_A.ID_NO = revised.ID_NO
and TABLE_A.ENTRY_DATE = revised.ENTRY_DATE