I have two tables:
id
1
2
3
4
t1 AND t2
id | related_id
1 | 2
1 | 3
Where t2 is relationship table between t1 records. What is the best way to get desired output?
t1.id | t1_copy.id
1 | NULL -- want to get this NULL row
1 | 2
1 | 3
Simple JOIN would almost work, however it doesn't give me the first NULL row.
SELECT t1.id, t1_copy.id FROM t1
LEFT JOIN t2 ON t1.id = t2.id
LEFT JOIN t1 t1_copy ON t1_copy.id = t2.related_id
WHERE t1.id = 1
P.S: Yes, I do realize that desired output is wacky.
Seems like a simple UNION should do the trick
SELECT
id,
null as copy_id
FROM
t1
WHERE
exists (select * from t2 where t1.id = t2.id)
UNION ALL
SELECT
t1.id,
t2.related_id
FROM
t1
INNER JOIN t2
ON t1.id = t2.id
SQL Fiddle
SELECT DISTINCT t1.id, t1_copy.id FROM t1
LEFT OUTER JOIN t2 ON t1.id = t2.id
WHERE t1.id = 1
Related
Let's say I have Two tables T1 and T2 with ID as the column. For example
T1:ID
1
2
3
4
5
T2:ID
4
5
6
7
8
How can get a column where my result is 1 2 3 6 7 8 I want to exclude the common IDs from both the table and display the result in one column.
Hmmm . . . one method is union all:
select t1.id
from table1 t1
where not exists (select 1 from table2 t2 where t2.id = t1.id)
union all
select t1.id
from table2 t2
where not exists (select 1 from table1 t1 where t2.id = t1.id);
use minus
select id from
(
select id from t1
union
select id from t2
) a
minus select id from (
select id from t1 join t2 on t1.id=t2.id
) b
If your DBMS support FULL OUTER JOIN then i would do :
select coalesce(t1.id, t2.id)
from t1 full outer join
t2
on t2.id = t1.id
where (t1.id is null or t2.id is null);
how to solve 3 table and group same id?
t1
----------
Id a
1 100
1 600
2 800
t2
----------
Id b
1 600
2 700
3 400
t3
----------
Id c
2 400
3 800
4 100
i want result like this:
Id a b c
------------------------------
1 700 600
2 800 700 400
3 400 800
4 100
Same id group by
do the fact you have id in several table youn should get, eg: using union ,all the id you need for join
select t.id, t1.a, t2.b, t3.c
from (
select id
from t1
union
select id
from t2
union
select id
from t3 ) AS t
left join t1 on t.id = t1.id
left join t2 on t.Id = t2.Id
left join t3 on t.Id = t3.Id
and if you need sum for a,b,c
select t.id, sum(t1.a), sum(t2.b), sum(t3.c)
from (
select id
from t1
union
select id
from t2
union
select id
from t3 ) AS t
left join t1 on t.id = t1.id
left join t2 on t.Id = t2.Id
left join t3 on t.Id = t3.Id
group by t.id
To ensure that you are taking all possible values use full outer join. Though this will not work in mySQL. If that is the case then look at this answer
select coalesce(t1.id,t2.id,t3.id) as id, sum(t1.a) as a, sum(t2.b) as b,sum(t3.c) as c
from t1
outer join t2
on t1.id = t2.id
outer join t3
on t1.id = t3.id
or t2.id = t3.id
group by id
Might be misunderstanding you, but looks like you just need to join the table more than doing a Union Operation on them. Below statement will only return records where all three tables have at least one record with the same id.
SQL would be:
SELECT TBL1.ID,
TBL1.A,
TBL2.B,
TBL3.C
FROM A TBL1 (NOLOCK)
INNER JOIN B TBL2 (NOLOCK) ON TBL1.ID = TBL2.ID
INNER JOIN C TBL3 (NOLOCK) ON TBL1.ID = TBL3.ID
Two questions:
1. Which SQL engine to you use?
2. and do you need to return values where one table does not have the id?
I am trying to join two tables such that I am getting only a first match from the Right table instead of every match in Table2.
So if the query is:
SELECT T1.Name, T2.Dates
FROM Table1 T1
LEFT JOIN Table2 T2 ON T1.ID = T2 = ID
WHERE T1.Name = 'John'
I would like to see
John | 14/11/14
Joe | 10/10/2014
Jane | 25/10/2014
Instead of
John | 14/11/2014
John | 12/10/2014
Joe | 10/10/2014
Jane | 25/10/2014
Jane | 26/10/2014
Which join should I use?
You need to decide which row, you should select. Min or max as commented.
SELECT T1.Name,
( SELECT MIN( T2.Dates) FROM Table2 T2 WHERE T1.ID = T2 = ID) AS Dates
FROM Table1 T1
WHERE T1.Name = 'John'
The ANSI standard function row_number() can be a big help here. It is supported by most databases, so you can do:
SELECT T1.Name, T2.Dates
FROM Table1 T1 LEFT JOIN
(SELECT t2.*, ROW_NUMBER() OVER (PARTITION BY t2.ID ORDER BY t2.DATE DESC) as seqnum
FROM Table2 t2
) T2
ON T1.ID = T2.ID AND seqnum = 1
WHERE T1.Name = 'John';
In your question, you have only one column from the second table, so you can also do this with aggregation:
SELECT t1.ID, t1.Name, MAX(t2.Date)
FROM Table1 T1 LEFT JOIN
Table2 T2
ON t1.ID = t2.ID
WHERE T1.Name = 'John'
GROUP BY t1.ID, t1.Name;
Query
SELECT a.name,
MAX(b.Dates)
FROM tbl1 a
JOIN tbl2 b
ON a.id=b.id
WHERE a.name='John'
GROUP BY a.name;
Demo
I have the following tables:
T1
ID PRIORITY
1 1
2 1
3 2
4 4
T2
ID SERVICE
1 PSTN
1 ADSL
3 ADSL
T3
ID DEVICE
1 BSC1
3 BSC7
4 BSC7
I want as output
ID PRIORITY SERVICE/DEVICE
1 1 PSTN
1 1 ADSL
1 1 BSC1
2 1
3 2 ADSL
3 2 BSC7
How to bind those tables using UNION ALL? Also I must put WHERE clause for T1 WHERE PRIORITY!=4
Total number in output table for one id should be the summary of T2+T3 (FOR ID=1 2+1=3) but for ID=2 it also SHOULD exist in table output with blank second column.
Thank you
If you are okay using just a UNION and not UNION ALL this should give you what you want
SELECT t1.Id, t1.Priority, COALESCE(t2.Service, '') AS [Service/Device]
FROM t1
LEFT JOIN t2 ON t1.Id = t2.Id
WHERE t1.Priority != 4
UNION
SELECT t1.Id, t1.Priority, COALESCE(t3.Device, '') AS [Service/Device]
FROM t1
LEFT JOIN t3 ON t1.Id = t3.Id
WHERE t1.Priority != 4
SQL Fiddle example
select T1.id , T1.PRIORITY ,T2.SERVICE as service/Device from t1
left outer join T2 on T2.id=T1.id where T1.PRIORITY!=4
union all
select T1.id , T1.PRIORITY ,T3.DEVICE as service/Device from t1
left outer join T3 on T3.id=T1.id where PRIORITY!=4
Say we have the following tables t1 and t2:
t1:
id | column_1
-------------
1 | 1
2 | 2
t2:
id | column_2
-------------
2 | 2
3 | 3
and we want to find the following result:
id | column_1 | column_2
------------------------
1 | 1 |
2 | 2 | 2
3 | | 3
This basically is the union of a right join with a left join. The following code works but feels clumsy:
(
SELECT t1.id, t1.column_1, t2.column_2
FROM t1
LEFT JOIN t2 ON t1.id = t2.id
)
UNION
(
SELECT t2.id, t1.column_1, t2.column_2
FROM t1
RIGHT JOIN t2 ON t1.id = t2.id
)
Is there a better way to achieve this?
select a.id, t1.column_1, t2.column_2
from (
select id from t1
union
select id from t2
) a
left outer join t1 on a.id = t1.id
left outer join t2 on a.id = t2.id
Try this one:
SELECT t1.id, t1.column_1, t2.column_2
FROM t1
FULL OUTER JOIN t2 ON (t1.id = t2.id)
Edit: Doesn't work, MySQL does not know FULL OUTER JOIN.
Have a look here:
http://www.xaprb.com/blog/2006/05/26/how-to-write-full-outer-join-in-mysql/
Haven't tried this myself, but this might work:
SELECT t1.id, t1.column_1, t2.column_2, t2a.column_2
FROM t1
LEFT JOIN t2 ON t1.id = t2.id
RIGHT JOIN t2 AS t2a ON t1.id = t2a.id