How to use multiple max Function in SQL select with left join - sql

Question

Suppose I have the following three tables:
Table1:
ID
Value_1
11
abc
22
def
33
xyz
Table2:
ID
Date_1
11
12-Mar-22
11
01-Jan-23
22
19-Dec-22
22
07-Feb-23
33
07-Mar-22
Table3:
ID
Length_1
11
574
11
1029
22
9220
33
1093
33
876
Now, I need an SQL query that would select each ID with Max Lenth_1 and Max Date_1.
Desired output:
ID
Value_1
Date_1
Length_1
11
abc
01-Jan-23
1029
22
def
07-Feb-23
9220
33
xyz
07-Mar-22
1093
I have used max() fuction to achieve this with left join between 2 tables together, however struggling when I have to use Max () twice with 3 tables. I am relatively new to SQL.
SQL Select Max(Date) out of rows with Duplicate Id
I tried this for two tables

Answer 1

Aggregate before you join the tables:
SELECT t1.id,
t1.value_1,
t2.date_1,
t3.length_1
FROM table1 t1
INNER JOIN (
SELECT id,
MAX(date_1) AS date_1
FROM table2
GROUP BY id
) t2
ON (t1.id = t2.id)
INNER JOIN (
SELECT id,
MAX(length_1) AS length_1
FROM table3
GROUP BY id
) t3
ON (t1.id = t3.id)
Which, for the sample data:
CREATE TABLE Table1 (ID, Value_1) AS
SELECT 11, 'abc' FROM DUAL UNION ALL
SELECT 22, 'def' FROM DUAL UNION ALL
SELECT 33, 'xyz' FROM DUAL;
CREATE TABLE Table2 (ID, Date_1) AS
SELECT 11, DATE '2022-03-12' FROM DUAL UNION ALL
SELECT 11, DATE '2023-01-01' FROM DUAL UNION ALL
SELECT 22, DATE '2022-12-19' FROM DUAL UNION ALL
SELECT 22, DATE '2023-02-07' FROM DUAL UNION ALL
SELECT 33, DATE '2022-03-07' FROM DUAL;
CREATE TABLE Table3 (ID, Length_1) AS
SELECT 11, 574 FROM DUAL UNION ALL
SELECT 11, 1029 FROM DUAL UNION ALL
SELECT 22, 9220 FROM DUAL UNION ALL
SELECT 33, 1093 FROM DUAL UNION ALL
SELECT 33, 876 FROM DUAL;
Outputs:
ID
VALUE_1
DATE_1
LENGTH_1
11
abc
2023-01-01 00:00:00
1029
22
def
2023-02-07 00:00:00
9220
33
xyz
2022-03-07 00:00:00
1093
fiddle

Answer 2

One option is to use subqueries selecting max values from tables 2 and 3:
Select t1.ID, t1.VALUE_1,
(Select Max(DATE_1) From Table2 Where ID = t1.ID) "DATE_1",
(Select Max(LENGTH_1) From Table3 Where ID = t1.ID) "LENGTH_1"
From Table1 t1
Order By t1.ID
... another one is to use analytic function with distinct keyword but it could be performance costly with big datasets:
Select DISTINCT
t1.ID, t1.VALUE_1, Max(t2.DATE_1) OVER(Partition By t1.ID) "DATE_1", Max(t3.LENGTH_1) OVER(Partition By t1.ID) "LENGTH_1"
From Table1 t1
Inner Join Table2 t2 ON(t2.ID = t1.ID)
Inner Join Table3 t3 ON(t3.ID = t1.ID)
Order By t1.ID
... both with your sample data:
WITH
Table1 (ID, VALUE_1) AS
(
Select 11, 'abc' From Dual Union All
Select 22, 'def' From Dual Union All
Select 33, 'xyz' From Dual
),
Table2 (ID, DATE_1) AS
(
Select 11, To_Date('2022-03-12', 'yyyy-mm-dd') From Dual Union All
Select 11, To_Date('2023-01-01', 'yyyy-mm-dd') From Dual Union All
Select 22, To_Date('2022-12-19', 'yyyy-mm-dd') From Dual Union All
Select 22, To_Date('2023-02-07', 'yyyy-mm-dd') From Dual Union All
Select 33, To_Date('2022-03-07', 'yyyy-mm-dd') From Dual
),
Table3 (ID, LENGTH_1) AS
(
Select 11, 574 From Dual Union All
Select 11, 1029 From Dual Union All
Select 22, 9220 From Dual Union All
Select 33, 1093 From Dual Union All
Select 33, 876 From Dual
)
results as:
ID VALUE_1 DATE_1 LENGTH_1
---------- ------- --------- ----------
11 abc 01-JAN-23 1029
22 def 07-FEB-23 9220
33 xyz 07-MAR-22 1093

Answer 3

Select t1.id, t1.value1, max(t2.date_1) date_1, max(t3.length_1)t3
from table_1 t1
left join table_2 t2 on t1.id=t2.id
left join table_3 t3 on t1.id=t3.id
group by t1.id, t1.value1
order by 1