SQL inner join with filtering - sql

Question

I have 2 tables as follows:
Table1:
ID Date
1 2022-01-01
2 2022-02-01
3 2022-02-05
Table2
ID Date Amount
1 2021-08-01 15
1 2022-02-10 15
2 2022-02-15 20
2 2021-01-01 15
2 2022-02-20 20
1 2022-03-01 15
I want to select the rows in Table2 such that only rows past the Date in Table1 are selected in Table2 and calculate a sum of amounts of each subset and max(date) in Table2 for each subset grouped by ID.
So the result would look like
ID Date Amount
1 2022-03-01 30
2 2022-02-20 40
SQL newbie here...I tried an inner join, but wasnt able to pass the date filter along...
Tried query:
with table1 as (select * from table1)
,table2 as (select * from table2)
select * from table1 a
inner join table2 b on (a.id=b.id)
Thanks!

Answer 1

Much like Paul, I would use a JOIN but I would put the clauses on the ON, so if you join to more tables, it's cleaner for the SQL optimizer to see what is the intent on a per table/join basis. I would also use aliases on tables and use the alias, so there is no room for confusion where the value is coming from, which again as a habit makes life easier when composing more complex SQL or cut'n'pasting into bigger blocks of code.
so with some CTE's for the data:
WITH table1(id, date) AS (
SELECT * FROM VALUES
(1, '2022-01-01'),
(2 , '2022-02-01'),
(3 , '2022-02-05')
), table2(id, date, amount) AS (
SELECT * FROM VALUES
(1, '2021-08-01'::date, 15),
(1, '2022-02-10'::date, 15),
(2, '2022-02-15'::date, 20),
(2, '2021-01-01'::date, 15),
(2, '2022-02-20'::date, 20),
(1, '2022-03-01'::date, 15)
)
The following SQL:
SELECT a.id,
max(b.date) as max_date,
sum(b.amount) as sum_amount
FROM table1 AS a
JOIN table2 AS b
ON a.id = b.id AND a.date <= b.date
GROUP BY 1
ORDER BY 1;
ID
MAX_DATE
SUM_AMOUNT
1
2022-03-01
30
2
2022-02-20
40

Answer 2

Here is how I would do this with Snowflake:
--create the tables and load data
--table1
CREATE TABLE TABLE1 (ID NUMBER, DATE DATE);
INSERT INTO TABLE1 VALUES (1, '2022-01-01');
INSERT INTO TABLE1 VALUES (2 , '2022-02-01');
INSERT INTO TABLE1 VALUES (3 , '2022-02-05');
--table 2
CREATE TABLE TABLE2 (ID NUMBER, DATE DATE, AMOUNT NUMBER);
INSERT INTO TABLE2 VALUES(1, '2021-08-01', 15);
INSERT INTO TABLE2 VALUES(1, '2022-02-10', 15);
INSERT INTO TABLE2 VALUES(2, '2022-02-15', 20);
INSERT INTO TABLE2 VALUES(2, '2021-01-01', 15);
INSERT INTO TABLE2 VALUES(2, '2022-02-20', 20);
INSERT INTO TABLE2 VALUES(1, '2022-03-01', 15);
Now obtain the data using a select
SELECT TABLE1.ID, MAX(TABLE2.DATE), SUM(AMOUNT)
FROM TABLE1, TABLE2
WHERE TABLE1.ID = TABLE2.ID
AND TABLE1.DATE < TABLE2.DATE
GROUP BY TABLE1.ID
Results
ID
MAX(TABLE2.DATE)
SUM(AMOUNT)
1
2022-03-01
30
2
2022-02-20
40

Answer 3

Not personally familiar with Snowflake but a standard SQL query that should work would be:
select id, Max(date) Date, Sum(Amount) Amount
from Table2 t2
where exists (
select * from Table1 t1
where t1.Id = t2.Id and t1.Date < t2.Date
)
group by Id;
Note that because you are only requiring data from Table2, an exists is preferable over an inner join and in almost all cases will be more performant than a join, at worst the same.