I am trying to UPDATE Table A with records in Table B based on a LEFT OUTER JOIN based on two columns of data. So, for example, the JOIN from Table A might be USA-4 to match Table B's USA-4. Returning a result of XYZ to a different column. The problem I am having is the Table B contains multiple USA-4's and as a result Table A appears to be updating more than once. Is there a way to fix this? A different JOIN type?
UPDATE tablea a
SET USA-4 = (SELECT distinct USA-4 FROM tableb b WHERE a.id=b.id)
Related
I face issue about duplicate data when join table, here my sample data table I have
-- Table A
I want to join with
-- Table B
this my query notation for join both table,
select a.trans_id, name
from tableA a
inner join tableB b
on a.ID_Trans = b.trans_id
and this the result, why I get the duplicating data which should show only two lines of data, please help me to solve this case.
Firstly, as you have been told multiple times in the comments, this is working exactly as you have written, and (more importantly) as intended. You have 2 rows in tableA and those 2 rows match 2 rows in your table tableB according to the ON clause. This means that each join operation, for the each of the rows in tableA, results in 2 rows as well; thus 4 rows (2 * 2 = 4).
Considering that your table, TableA only has one column then it seems that you should be cleaning up that data and deleting the duplicates. There are plenty of examples on how to do that already (example).
Perhaps the column you show us in TableA is one many, and thus instead you have a denormalisation issue, and instead there should be another table with the details of Id_trans and a PRIMARY KEY or UNIQUE CONSTRAINT/INDEX on it. Then you would join fron that table to TableB.
Finally, what you might be after is an EXISTS, which would look like this:
SELECT B.trans_id, B.[name]
FROM dbo.TableB B
WHERE EXISTS(SELECT 1
FROM dbo.TableA A
WHERE A.ID_Trans = B.trans_id); --Odd that it's called ID_Trans in one table, and Trans_ID in another
As the comments mentioned your query does exactly what you asked it to do but I think you wanted something like:
select a.trans_id, a.name, b.name
from tableA a
inner join tableB b on a.trans_id = b.trans_id
group by a.trans_id, a.name, b.name
Since there are two rows in both table with same ID join will make them four. You can use distinct to remove duplicates:
select distinct a.trans_id, name
from tableA a
inner join tableB b
on a.id_trans = b.trans_id
But I would suggest to use exists:
select trans_id, name
from tableB b
exists (select 1 from tableA a where a.trans_id=b.trans_id)
I have two tables, TableA:
- Original_Location
- Units
and TableB:
- Original_Loc
- Adjacent_Loc
- Direction (up/down/left/right from original loc)
My goal is to return the original location, the adjacent location, the direction, and the number of units at the adjacent loc. So far, I've only been able to return the units from the original loc.
Here is what I've tried so far:
Select Original_Location,
Units,
TableB.Adjacent_Loc,
TableB.Direction
From TableA
Inner Join
Select *
From TableB
On TableA.Original_Location = TableB.Original_Loc
My thought is that I might need to change the fields I'm selecting before the inner join, or potentially join on Original_Location = Adjacent_Loc.
Your Join syntax is not right. First you don't need to "select" anything from Table B, your initial SELECT is getting data from the joined tables (A and B) as if they were 1 table. Secondly, you need to specify which fields to join the tables with.
Your join will be something like :-
From TableA Inner Join TableB
on TableA.Original_Loc = TableB.Original_Loc
Once you have got your joins right, you need to make another join to TableA to get the Units. This time you are joining the Adjacent_Loc in Table B to the Original_Location in Table A - which will have the Units value you need.
My example below uses aliases to identify each table (there are now 2 references to TableA so they need to be identified separately). So when you do the second join to TableA, this has the alias of c to differentiate it from the first TableA reference. You then need to select the Units from c.
Select a.Original_Location, c.Units, b.Adjacent_Loc, b.Direction
From TableA a Inner Join TableB b On a.Original_Location = b.Original_Loc
inner join TableA c on b.Adjacent_Loc = c.Original_Location
I need to know the rows in TABLE A that have join records in TABLE B based a column value in TABLE B, but I also need to return rows in which a row in TABLE A has no match in TABLE B.
It seems like I need a LEFT JOIN and a LEFT OUTER JOIN, so I'm not sure what to do there. I understand how to do each, but don't understand how to do them together.
The schema looks like:
TABLE_A
pk
TABLE_B
pk
a_fk
some_value
I need the joined rows where Table_A has no join record in Table_B OR Table_A has a join record row in Table_B (it can have many) in which some_value does not equal "thisValue"
Thanks.
A Left join is a left outer join. Outer joins preserve one of the tables which is what you are after so good guess.
SELECT *
FROM Table A
LEFT JOIN Table B
ON TableA.Column = TableB.Column
AND B.SomeValue <> 'ThisValue'
All of the rows with a match will have the B information populated all of those without will have nulls in the B data
I'm trying to left join two tables. Table A contains unique 100 records with field_a_1, field_a_2, field_a_3. The combination of field_a_1 and field_a_2 is unique.
Table B has multi-million records with multiple fields. field_b_1 is same as field_a_1 and field_b_2 is same as field_a_2.
I join the two tables together like this:
select a.*, b.*
from a
left join b
on field_a_1 = field_b_1
and field_a_2 = field_b_2
Instead of getting 100 records, I get multi-million records. Why is this?
Because table B has multiple rows for each table A entry.
For example:
TableA (ID)
1
2
3
TableB (ID, data)
1 hello
1 world
1 foo
1 bar
2 data
2 words
2 more
3 words
3 boring
If you left join from TableA to TableB, you will get a row for every TableB record that matches a TableA record - ie. all of them.
Can you explain what results you are looking for?
Because a left join returns all of the rows from the first table + all of the matching rows from the second table. Which of the millions of matching rows did you expect to get?
Left join or inner join don't really make a difference. A JOIN will return all rows that match the join condition. So if table b has millions of rows that match the JOIN criteria, then all the rows will be returned.
Depending on what you wish to accomplish you should consider using the DISTINCT keyword or GROUP BY to perform aggregate functions.
I'm trying to do
SELECT * FROM a, b
However, it doesn't return anything if one of the tables is empty. How do I make it so it returns 'a' even if the other one is empty?
Using two tables in the from clause is functionally equivalent to a cross join:
select *
from A
cross join
B
This returns a row of A for every row in B. When B is empty, the result is empty too. You can fix that by using a left join. With a left join, you can return rows even if one of the tables is empty. For example:
select *
from A
left join
B
on 1=1
As the condition 1=1 is always true, this is just like a cross join except it also works for empty tables.
SELECT * FROM a LEFT JOIN b ON a.ID = b.ID
Will return everything from a even if b is empty.
You should do a left join.
Like this
SELECT *
FROM A
LEFT JOIN B ON A.ID = B.ID
Then you receive the rows in A and the respective row in B if exists.
SELECT a.*, b.* FROM a LEFT JOIN b ON a.id = b.id
in this example id is just example name for join key
The query mentioned above display join of both tables if a contain 2 record and b contain 7 records it displays 7*2 = 14 records. In your case one of the table is empty( with 0 records), it will not display any data. If still you want to display data and tables are not having any relationship, you need to check if count of both tables greater that 0. Otherwise display records from only one table which is not empty.