Sum on Multiple Left Joins - sql

Question

I am trying to sum the total value of a column for a specific ID after multiple left joins.
The below code gives me what I am looking for but across multiple rows, I need the value for T3.C_Amt and T4.E_Amt to be totaled.
SELECT
T1.ID,
T2.Unique_ID,
T3.C_Date,
T3.C_Amount,
T4.D_Date,
T4.D_Amount
FROM
TABLE_1 T1
LEFT JOIN DATABASE1.TABLE_2 T2
ON T1.ID = T2.UNIQUE_ID
LEFT JOIN DATABASE1.TABLE_3 T3
ON T2.Unique_ID = T3.Unique_ID
AND T3.C_Date = '2019-04-11'
LEFT JOIN DATABASE1.TABLE_4 T4
ON T2.Unique_ID = T4.Unique_ID
AND T4.D_Date= '2019-04-11'
--this needs to be summed to have the total amount
I want it to return one row for the Unique ID with total C_Amount and total D_Amount for the specific date

Answer 1

Use aggregation with group by
SELECT T2.Unique_ID,T3.C_Date,sum(T3.C_Amount),
T4.D_Date,sum(T4.D_Amount)
FROM TABLE_1 T1
LEFT JOIN DATABASE1.TABLE_2 T2
ON T1.ID = T2.UNIQUE_ID
LEFT JOIN DATABASE1.TABLE_3 T3
ON T2.Unique_ID = T3.Unique_ID AND T3.C_Date = '2019-04-11'
LEFT JOIN DATABASE1.TABLE_4 T4
ON T2.Unique_ID = T4.Unique_ID AND T4.D_Date= '2019-04-11'
group by T2.Unique_ID,T3.C_Date,T4.D_Date

Answer 2

I would do it this way. Since Teradata is a MPP, there should not be much of a performance impact as well.
SELECT Unique_ID,C_Date,sum(C_Amount),D_Date,sum(D_Amount)
FROM
(
SELECT
T1.ID ID,
T2.Unique_ID Unique_ID,
T3.C_Date C_Date,
T3.C_Amount C_Amount,
T4.D_Date D_Date,
T4.D_Amount D_Amount
FROM
TABLE_1 T1
LEFT JOIN DATABASE1.TABLE_2 T2
ON T1.ID = T2.UNIQUE_ID
LEFT JOIN DATABASE1.TABLE_3 T3
ON T2.Unique_ID = T3.Unique_ID
AND T3.C_Date = '2019-04-11'
LEFT JOIN DATABASE1.TABLE_4 T4
ON T2.Unique_ID = T4.Unique_ID
AND T4.D_Date= '2019-04-11'
) ABC
GROUP BY Unique_ID,C_Date,D_Date

Answer 3

I would add a concern of 1-to-many causing a false total. What if table 3 has 10 records for a given T2.UniqueID and another 5 for the T4 table. You have just compounded your total completely out of range.
As such, I would pre-aggregate from the child tables grouped by the unique ID filtered on the date. Also, you can remove the T2 table due to associative properties.
T1.ID = T2.Unique_ID = T3.Unique_ID = T4.Unique_ID
to T1.ID = T3.Unique_ID = T4.Unique_ID
SELECT
T1.ID,
T3.C_Date,
T3.C_Amount,
T4.D_Date,
T4.D_Amount
FROM
TABLE_1 T1
LEFT JOIN
( Select Unique_ID, sum( C_Amount ) as T3Sum
from DATABASE1.TABLE_3
where T3.C_Date = '2019-04-11'
group by Unique_ID ) T3
ON T1.ID = T3.Unique_ID
LEFT JOIN
( select Unique_ID, sum( D_Amount ) T4Sum
from DATABASE1.TABLE_4
where D_Date= '2019-04-11'
group by Unique_ID ) T4
ON T1.ID = T4.Unique_ID
Now, your ambiguity on table names might help being more real-life descriptive. Your summary amounts are based on a single date, but how many records in T1 that are applicable? If you have 5k rows in T1 and only 450 entries total between tables T3 and T4, your result set would still give you all the rows. That being said, you probably dont want the bloat of records that don't have any such details in the secondary sum subqueries. I would add a WHERE clause at the end
WHERE
T3.Unique_ID IS NOT NULL
OR T4.Unique_ID IS NOT NULL