SQL select newst data in 2 table same primary key - sql

Question

I have two same table:
A(id, ..., modified_date)
and B(id, ..., modified_date). I need to select the record with same id but modified_date larger.
How can I write the SQL? Please help.
Example:
Table A
id | user name | email | modified date
------------------------------------------------
1 | Anne | ana#gmail.com | 2016/12/20
And table B
id | user name | email | modified date
------------------------------------------------
1 | Anne Jr, | ana_j#gmail.com | 2017/01/20
With two record has same id, I need to get the record with modified_date larger. The example above, with id = 1, I need to select the record has modified_date = 2017/01/20

Answer 1

You can do a JOIN and then ORDER BY modified_date column like
select t1.id,t1.modified_date
from table1 t1 join table2 t2 on t1.id = t2.id
order by t1.modified_date desc;

Answer 2

If you need data from the B table, you can use :
SELECT b.*
FROM B b
WHERE b.id = a.id
AND b.modified_date > a.modified.date
Similarly, if you need data from the A table you can use :
SELECT a.*
FROM A a
WHERE a.id = b.id
AND a.modified_date > b.modified.date
In case there are multiple records which fit the criteria and you need only the one record which has the greatest modified date value then you can use :
SELECT TOP 1 a.*
FROM A a
WHERE a.id = b.id
AND a.modified_date > b.modified.date
ORDER BY a.modified_date
OR
SELECT TOP 1 b.*
FROM B b
WHERE b.id = a.id
AND b.modified_date > a.modified.date
ORDER BY b.modified_date
Hope this helps!!!

Answer 3

You can try using a CASE expression on SQL Server
SELECT A.id,A.other_columns,
(CASE WHEN a.modified_date > b.modified_date THEN a.modified_date ELSE b.modified_date END) as modified_date
FROM [A] INNER JOIN [B] on A.id=B.id

Answer 4

If you want the higher of those two values, then use greatest() with a join:
select ta.id,
greatest(ta.modifed_date, tb.modified_date)
from table_a ta
join table_b tb on ta.id = tb.id;
If you want all columns from the row with the later date, you can use a case statement:
select ta.id,
case
when ta.modified_date > tb.modified_date then ta.email
else tb.email
end as email,
case
when ta.modifed_date > tb.modified_date then ta.user_name
else tb.user_name
end as user_name,
greatest(ta.modified_date, tb.modified_date) as modified_date
from table_a ta
join table_b tb on ta.id = tb.id;