lets say i have table like this
Table A:
column_a
1
2
3
Table B:
column_b
a
b
c
and i want to have result like this:
column_a column_b
1 a
1 b
1 c
2 a
2 b
2 c
3 a
3 b
3 c
does it possible to join two table without relation like this using query?
Yes, you're looking for cross join
select a.column_a, b.column_b
from a
cross join b
order by a.column_a, b.column_b;
Related
i have following SQL table A in my database:
index, group, foo
1 A 2
2 A 2
3 A 0
4 A 1
5 B 2
6 B 1
7 C 1
There are few more groups and I need to write a query based on this filter table B. For each group in table A it's index should be equal or greater than index_egt from table B for the same group.
If the group is not listed in table B, the group won't be filtered.
index_egt, group
3 A
5 B
Expected result:
index, group, foo
3 A 0
4 A 1
5 B 2
6 B 1
7 C 1
Try this, the A.index>=B.index_egt will handle cases where the group is listed in TableB and the B.index_egt IS NULL will handle cases where the group is not listed:
SELECT
A.index,
A.group,
A.foo
FROM TableA AS A
LEFT JOIN TableB AS B ON A.group=B.group
WHERE A.index>=B.index_egt
OR B.index_egt IS NULL
select
a.*
from
A a
left join
B b ON b.group = a.group
where
a.index >= b.index_egt OR b.index_egt IS NULL
I always like this trick with coalesce
SELECT a.*
FROM a_table_with_no_name a
LEFT JOIN b_table_with_no_name b ON b.group = a.group
WHERE a.index >= COALESCE(b.index_egt,a.index)
Consider below 3 tables.
Table a
Col a Col b Col c
1 000 Actual data
1 001 Actual data
2 000 Actual data
3 000 Actual data
3 001 Actual data
3 002 Actual data
Table b
Col a Col b Col d
1 000 Actual data
1 001 Actual data
2 000 Actual data
Table c
Col a Col b Col d
3 000 Actual data
3 001 Actual data
3 002 Actual data
Table a is parent table and table b and c are child table having col a & b common among 3 and needs to be joined.
Now Join should be such if data is not found in table b then only it should be searched in table c
Desired:
cola col b col c col d
1 000 somedata moredata
1 001 somedata moredata
2 000 somedata moredata
3 000 somedata moredata
3 001 somedata moredata
3 002 somedata moredata
Well, currently what i am doing is, left join b to a and c to a, but i think every time for record in a will be searched in b and c both making it Less cost effective. hence want to make it cost effective/fine-tune such that if records NOT exist in b then only search c.
What you really need is a way to "collect" all the rows from table B, and if there are none, then all the rows from table C. Doing the join to A is then standard.
Something like this should work. Make it a subquery and join to your first table.
select col_a, col_b, col_c
from table_b
union all
select col_a, col_b, col_c
from table_c
where (select count(*) from table_b) = 0
If table_b has at least one row, then nothing will be selected from table_c (because the where condition will be false for all rows in table_c). However, if table_b is empty, all the rows from table_c will be selected.
What you need to do is first create a union of two tables B and C with only those records where are in B and C but if they are in B then we should ignore the C ones then do a join with Table A. Thus:
SELECT B.cola, B.colb from B
UNION ALL
SELECT C.cola, C.colb from C
Now using this table, you can join with Table A like:
SELECT A.cola, A.colb, tmp.colc
FROM A
JOIN
( SELECT B.cola, B.colb, B.colc from B
UNION ALL
SELECT C.cola, C.colb from C) AS tmp
ON A.cola = tmp.cola
AND A.colb = tmp.colb
Two left joins:
select a.*, b.*, c.*
from a
left join b
on a.cola=b.cola
and a.colb = b.colb
left join c
on a.cola=c.cola
and a.colb=c.colb
I have 2 tables like below:
Table 1
---------
1
2
3
Table 2
--------
A
B
C
How do i join to get an output like below:
Output
---------
1 A
1 B
1 C
2 A
2 B
2 C
3 A
3 B
3 C
Use Cross join:
SELECT *
FROM Table1
CROSS JOIN Table2
You can change the order by replacing * with table fields.
Read more about Cross Join.
OR you could do this:
SELECT Table1.*,Table2.*
FROM Table2,Table1
Result:
ID NAME
1 A
1 B
1 C
2 A
2 B
2 C
3 A
3 B
3 C
You want to do a CROSS JOIN and that will give you the Cartesian product of all the rows.
See http://en.m.wikipedia.org/wiki/Join_(SQL)
select * from table 1,table 2 .
For o/p like A 1
A 2
A 3
B 1
B 2
B 3
C 1
C 2
C 3
just
Does PostgreSQL support self joining or is there another way to solve this?
For example, lets say I have a single table (table a) with the following columns:
id name supid
------------------------
1 a 2
2 b 3
3 c 4
4 d 5
.. .. ..
Is there a way to output the data in the following format?
id name sup name
-------------------------
1 a b
2 b c
3 c d
4 d ..
.. .. ..
How about a simple JOIN?
SELECT a.id,a.name,b.name "sup name"
FROM tablea a
JOIN tablea b
ON a.supid = b.id
An SQLfiddle to test with.
I have the following tables in a Hive database:
table1:
id t X
1 1 a
1 4 a
2 5 a
3 10 a
table2:
id t Y
1 3 b
2 6 b
2 8 b
3 15 b
And I would like to merge them to have a table like:
id t Z
1 1 a
1 3 b
1 4 a
2 5 a
2 6 b
2 8 b
3 10 a
3 15 b
Basically what I want to do is :
a join on the column id (that part is easy)
merge the columns table1.t and table2.t into a new column t
have the variable Z that is equal to table1.X if the corresponding t comes from table1.t, and table2.Y if it comes from table2.t
order the table by id and then by t (that shouldn't be too hard)
I have no idea on how to do the parts 2 and 3. I tried with an outer join on
table1.id = table2.id and table1.t = table2.t, but it doesn't merge the two columns t.
Any pointer would be appreciated. Thanks!
CREATE TABLE table3 as SELECT * FROM (SELECT id,t,X as Z FROM t3_1 UNION ALL SELECT id,t,Y as Z FROM t3_2) u1 order by id,t;
Although not always required, using a subquery for the union'd queries help to organize, plus you can then reference the fields from the union (e.g. u1.id ) in other parts of the query.
You'll need the alias on the 3rd column to make the schemas match. If the source table name was not already a column, you could do something like this:
select * from (select id,t,'a' from t3_1 UNION ALL select id,t,'b' from t3_2) u1;
Try this one. It will insert in table 3, all the values from the other 2 tables
INSERT INTO table3 ( t, Z )
SELECT t, X
FROM table1
UNION ALL
SELECT t, Y
FROM table2