I have 2 simple tables:
table a:
id | txt
---+----
0 | aaa
1 | bbb
2 | ccc
table b:
id | tel
---+----
0 | 000
2 | 111
I am trying to join 2 tables like this:
SELECT a.*,b.*
FROM a,b
WHERE a.id=b.id
It works, but, if there is no entry in the "b" table it wont show anything.
what the sql shows is something like this:
id | txt | tel
---+-----+----
0 | aaa | 000
2 | ccc | 111
I also want to list the "empty" row a.id=1:
id | txt | tel
---+-----+-----
1 | bbb | NULL
Any ideas? Thanks!
(SQL is for MS Access / oledb)
You want a left outer join (or a full outer join, if you want rows in which there is no entry in the a table also).
SELECT a.*,b.* FROM a LEFT OUTER JOIN b ON a.id=b.id
Depending the system, the syntax LEFT JOIN may work as well.
In MSAccess query designer, right click on the relationship connection between the two tables, and edit its properties. Modify it to 'show all records from table a'.
This:
SELECT a.*,b.*
FROM a, b
WHERE a.id = b.id
...is ANSI-89 inner join syntax, and I highly recommend using ANSI-92 syntax instead:
SELECT a.*,
b.*
FROM TABLE_A a
JOIN TABLE_B b ON b.id = a.id
...mostly because ANSI-88 syntax for left joining to tables wasn't consistently implemented on various databases. This will return the results you expect:
SELECT a.id,
a.txt,
b.tel
FROM TABLE_A a
LEFT JOIN TABLE_B b ON b.id = a.id
A LEFT JOIN means you'll get all the records from TABLE_A in this example, and when there is a matching record (based on the ON criteria) in TABLE_B, the value will be displayed. Otherwise, the TABLE_B column references will return NULL values.
For more information on JOINs, see this page for a great pictorial demonstration of what each one represents and how they compare.
Related
I need help writing a query to display results I want.
"Table 3 - relations" keeps all relations between table 1 and 2.Often, relation between table 1 and 2 will not exist in table 3 so I want to see missing relation in the results for all Table 1 rows - see expected Results below.
I can't modify these tables - I have only SELECT privilege.
Data and expected result below:
Table 1 - a:
a_id, a_name
e.g.:
1 A
2 B
Table 2 - b:
b_id, b_name
e.g.:
1 X
2 Y
Table 3 - relation:
asset1_id (it's always id from Table 1), asset2_id (it's always id from Table 2), relation_type
e.g.:
1 1 covers
1 2 covers
Expected result:
Table1_name, Table2_name, Table3_relation_type (including NULL for b_name and relation_type when such relation does not exist in Table 3 - relation)
e.g.
A X covers
A Y covers
B NULL NULL
I can't get the 3rd expected line with NULLs.
I think that this query will produce those results.
select a.name as a_name,b.name as b_name, r.relation_type from relation r
join a on a.id=r.asset1_id
join b on b.id=r.asset2_id
union
select a.name as a_name,b.name as b_name,r.relation_type from relation r
full outer join a on a.id=r.asset1_id
full outer join b on b.id=r.asset2_id
where a.id is null or b.id is null
With your data sample you could try this one.
It should work both hive or impala.
SELECT t1.name ,t2.name ,r.relation_type
FROM relation r
FULL OUTER JOIN table1 t1 ON(t1.id = r.id1)
FULL OUTER JOIN table2 t2 ON(t2.id = r.id2);
+------+------+---------------+
| name | name | relation_type |
+------+------+---------------+
| A | X | covers |
| A | Y | covers |
| B | NULL | NULL |
+------+------+---------------+
WITH
cte_A AS (
SELECT id as a_id, name as a_name
FROM a
),
cte_C AS (
SELECT c.asset_id1 as a_id, b.name, c.relation
FROM c
LEFT JOIN b ON c.id=b.asset_id2
)
SELECT cte_A.a_name, cte_C.name as c_name, cte_C.relation
FROM cte_A
LEFT JOIN cte_C ON cte_A.a_id=cte_C.a_id
I am attempting to create a view which that combines two tables to have the form below.
Table A (column FIRST)
FIRST
-----
A
B
C
Table B (column SECOND)
SECOND
-----
1
2
3
Result
FIRST | SECOND
------|-------
A | 1
A | 2
A | 3
B | 1
B | 2
B | 3
C | 1
C | 2
C | 3
I have been struggling to wrap my brain around this one. Something like the below code is what I would like to end up with for my view, to make it similar to my other views, but all the options I've tried haven't worked quite right.
SELECT
FIRST,
'' AS SECOND
FROM Table A
UNION ALL
SELECT
'' AS FIRST,
SECOND
FROM Table B
You are looking for a cross join:
select a.first, b.second
from a cross join
b
order by a.first, b.second;
You can use a CROSS JOIN. For example:
CREATE VIEW v AS
SELECT a.first, b.second
FROM tablea a
CROSS JOIN tableb b
Let’s say I have a simplified table structure as follows:
Table A - ID (PK)
Table B - ID (PK), AID = FK to Table A
Table C - ID (PK), BID = FK to Table B
Table D - ID (PK), CID = FK to Table C
Query something like so:
SELECT * FROM TABLE_A TBLA
LEFT JOIN TABLE_B TBLB ON TBLA.ID = TBLB.AID
LEFT JOIN TABLE_C TBLC ON TBLB.ID = TBLC.BID
LEFT JOIN TABLE_D TBLD ON TBLC.ID = TBLD.CID
It’s relatively straight-forward but what I want to do is somewhat a conditional join in that I want all records from TABLE A but want to join TABLE B -> TABLE C -> TABLE D if the first join between TABLE A and TABLE B is satisfied, bearing in mind that I could change TABLE B -> TABLE C -> TABLE D joins to be INNER as there’ll exist in that initial join between TABLE A and TABLE B is satisfied.-
But also I’d need a WHERE condition on TABLE D also.
So essentially want to eliminate the LEFT JOIN’S between TABLE_B, TABLE_C, TABLE_D where join isn’t satisfied between TABLE_A and TABLE_B.
Very simplified data so apologies!
| Table A |
| ID |
| 1 |
| 2 |
| 3 |
| 4 |
| 5 |
| Table B |
| ID | AID |
| 1 | 5 |
| Table C |
| ID | BID |
| 1 | 1 |
| Table D |
| ID | CID | Value |
| 1 | 1 | ABC |
The reason I want to eliminate the join is that for 4 of the 5 rows in Table A, I’m doing unnecessary joins across three tables to get the value in Table D.
You can use brackets with join, but not sure if that would help you!
SELECT * FROM
TABLE_A TBLA
LEFT JOIN (TABLE_B TBLB
INNER JOIN TABLE_C TBLC ON TBLB.ID = TBLC.BID
INNER JOIN TABLE_D TBLD ON TBLC.ID = TBLD.CID) ON TBLA.ID = TBLB.AID
This way, when you have A matches entries in B, but B is not matched in the chain to C and D, B data is not retrieved, and so for C
You mentioned that you need a where condition on table D? Does that mean that you always have to link to D?! Note that if you have a condition on D, the condition has to be satisfied in all cases. Hence, when no records are retrieved from D, no records will be retreived from the query (even with your initial outer join unless you used OR .. is null )
I've got these 3 tables:
Table A
---------------------------
|KEY | VALUE_A1 | VALUE_A2|
---------------------------
Table B
------------------------------
|KEY | APPLICATION | VALUE_B1|
------------------------------
Table C
------------------------------
|KEY | APPLICATION | VALUE_C1|
------------------------------
I want to return A.VALUE_A1, A.VALUE_A2 along with B.VALUE_B1 or C.VALUE_C1 based on the existence of the application in B or C. This application is given in de where-clause in de script.
Example:
Table A has 10 records. Table B contains 6 records with application 'APP1'. Table C contains 4 records with application 'APP2'. Both table B and C are through KEY connected to table A. If the application given is 'APP1' then I want to return B.VALUE_B1. If 'APP2' is given I want to return C.VALUE_C1.
Is it possible to INNER JOIN on one of two tables based on a CASE-like condition?
Not INNER JOIN but LEFT JOIN like this
select A.KEY
A.VALUE_A1, A.VALUE_A2,
CASE WHEN B.VALUE_B1 IS NOT NULL THEN B.VALUE_B1 ELSE C.VALUE_C1 END AS RESULT_VALUE
from A
LEFT JOIN B on A.key=B.key
LEFT JOIN C on A.key=C.key
UPDATE: There is an alternative
select A.KEY
A.VALUE_A1, A.VALUE_A2,
sub.VALUE AS RESULT_VALUE
from A
INNER JOIN (SELECT KEY, VALUE_B1 as VALUE
FROM B
UNION ALL
SELECT KEY, VALUE_C1 as VALUE
FROM C) sub on A.KEY=sub.KEY
I'm executing the following query
Select * from A a left outer join B b on (b.id = a.id)
I'm getting one record from A and no records from B. I'm expecting one record in final select query but getting none.
Here is some sample data:
A
v_id, id, date, d_id
1, 1244578, 02-MAR-11, 1827877
B, no data presented:
e_id,id,amount
What am I doing wrong? How can I get it do like this ?
This should work fine:
Select *
from A a
left outer join B b on b."id" = a."id"
See it in action here:
SQL Fiddle Demo
This will give you:
| V_ID | ID | DATE | D_ID | E_ID | AMOUNT |
----------------------------------------------------------
| 1 | 1244578 | 02-MAR-11 | 1827877 | (null) | (null) |
You are getting one record from Table A this is because table A has only one record and Table B have no record.
In left outer join content of first table is show in result join with second table but in your case second table have no records so final result show null values for that records.