I have 3 tables, A, B,C
Table A,Columns: latlong, name
Table B, columns : code, name
Table C, Columns : latlong, code
I want to update table A,column Name with the values from Table B, Column Name, something like:
update A set A.name =
(select b.name
from B where code = c.code)
where a.latlong = c.latlong
Note that all the columns are not related.
Would appreciate the right direction to go about it.
Have tried Sub queries with inner joins, but no good.
You can do this with an update using join:
update a
set name = b.name
from a join
c
on c.latlong = a.latlong join
b
on b.code = c.code;
Try update with INNER JOIN
update A set
A.name = B.name
FROM A
INNER JOIN C on C.latlong = A.latlong
INNER JOIN B on B.code = C.code
You have mentioned in your question the following:
I want to update table A,column Name with the values from Table B, Column Name
But what I can see from your query is that actually , you need only those values of the column Name of table B which has same value of code as in table C, and that your latlong in A should be the same as latlong in C, if I'm not mistaken.
Based on that, I can say you need an SQL JOIN operation for Tables B and C with table A. Something like this:
UPDATE A SET A.name = B.Name
FROM A
JOIN C
ON C.latlong = A.latlong
JOIN B
ON B.code = C.code
No need to create a SUBQUERY
Last condition is missing where Table A.Latlong = C.Latlong to pick up the correct code!
Related
I have three tables (a,b,c). I want to update a column in table a (named email) where
a.id = b.id, b.name = c.name.
This is what I have so far.
UPDATE a
SET email = "hi#gmail.com"
FROM a INNER JOIN b ON a.id = b.id
INNER JOIN c ON b.name = c.name
WHERE email IS NULL;
However I'm getting the error that table name a is specified more than once.
What can I do?
You don't specify the table being updated in the from clause. Use the where clause to correlated it:
UPDATE a
SET email = 'hi#gmail.com'
FROM b JOIN
c
ON b.name = c.name
WHERE a.id = b.id AND a.email IS NULL;
There are three tables, A,B and C having common columns(name and number)
Table A have 10 records(say x) which can be only from table B(say, y) and table C(say, z) (like, x = y+z).
In table A, there are some records whose value is 0 (zero)
I need to compare those zero value based records using column = name, with other two tables.
And check the column "number" for the same "name" is also zero (0) in table B and table C?
I tried to write the below sample query to test on my small set of 3 tables data- but for some reasons I am not able to get all the 10 records as a result?
SELECT a.name,a.number as A_number, b.number as B_number, c.number as C_number
from A a, B b, C c
WHERE a.name = b.name
The above query gives me data as follows in the sqlfiddle-
http://sqlfiddle.com/#!2/57f86/1
In the above data- theres no record name="hello"
Can anyone please correct me where I am going wrong? and how to get the exact result? I need all the records from Table A. I know if I use left join it will populate all the left table data even if no match.
Possibilities: Table A having records, some may be present in table B
and some in table C, but not on both.
I think this is what you want:
SELECT a.*, b.number as bnumber, c.number as cnumber
from a left outer join
b
on a.name = b.name left outer join
c
on a.name = c.name
where a.number = 0;
By the way, here is a Postgres SQL Fiddle.
It's been over 20 years since the JOIN keyword was added to SQL. Use it:
select
a.name,
a.number as A_number,
b.number as B_number,
c.number as C_number
from A a
left join B b on a.name = b.name
left join C c on a.name = c.name
where a.number = 0
The key here is the use of left join, which allows all rows in table A to be returned, even if there are no matching rows in the other tables.
If you want to just display true/false if the number is zero in the other tables, do this:
select
a.name,
a.number as A_number,
(b.number = 0 and c.number = 0) as zero_elsewhere
from A a
left join B b on a.name = b.name
left join C c on a.name = c.name
where a.number = 0
When you wrote WHERE a.name = b.name, that restricted the records returned from table A to only those that also exist in table B. This is not equivalent to a left join. If you used only a WHERE statement you would need to do:
WHERE ((a.name = b.name) OR (b.name is NULL))
AND
((a.name = c.name) OR (c.name is NULL))
In the comments and other answers, they have been using LEFT JOIN which is easier to write and read. I suggest you adopt that style as it is widely accepted.
I am unsure as to how to resolve an ambiguous column reference when using an alias.
Imagine two tables, a and b that both have a name column. If I join these two tables and alias the result, I do not know how to reference the name column for both tables. I've tried out a few variants, but none of them work:
Attempt 1
SELECT a.name, b.name
FROM (a INNER JOIN b ON a.id = b.id) AS x
This doesn't work as a and b are out of scope.
Attempt 2
SELECT x.a.name, x.b.name
FROM (a INNER JOIN b ON a.id = b.id) AS x
SQL syntax doesn't work like that.
Attempt 3
SELECT x.name, x.name
FROM (a INNER JOIN b ON a.id = b.id) AS x
That's just plain ambiguous!
I'm all out of ideas - any help would be much appreciated.
don't enclose it with parenthesis since (a INNER JOIN b ON a.id = b.id) is not a complete query.
SELECT a.name AS A_Name,
b.name AS B_Name
FROM a INNER JOIN b
ON a.id = b.id
or (assuming) if you have longer tables names and you want to make it short,
SELECT a.name AS A_Name,
b.name AS B_Name
FROM longTableNameA a
INNER JOIN longTableNameB b
ON a.id = b.id
I have a simple SQL question, I thought it would be quite straight forward but have got myself in a muddle. Any help would be appreciated
I have table A which contains a last updated
Table A has a one to many with Table B
Table B has a one to many with Table C
I want to show all rows of table C with the last updated time from table A. I have tried some joins but they dont seem to be quite working. Ideally I want somehting like
select a.lastUpdated c.* from TableA a, TableC c where
a.id in (select a_id from TableB where (select b_id from TableC where c_id = select
id from TableC where XXXX=YYYY))
so I can pass in an id for table C and then get one row returned with the last updated time present.
XXX=YYY would be my criteria for returning one row of table C.
Any help or pointers appreciated
Thanks
Something like
SELECT c.*
FROM TableA AS a
INNER JOIN TableB AS b
ON a.a_id = b.b_id
INNER JOIN TableC AS c
ON b.b_id = c.c_id
WHERE a.lastUpdated = c.lastUpdated;
Should work. This is a situation where a striaght INNER JOIN should suffice; unless of course I have missed something.
I hope this helps.
You should be able to do this by joining A and B together, aggregating the results at the c_id level, and then joining in C:
select tc.*, maxlastupdated
from tablec tc left outer join
(select tb.c_id, max(lastupdated) as maxlastupdated
from tablea ta join
tableb tb
on ta.b_id = tb.b_id
group by ta.id
) ta
on tc.c_id = ta.c_id
You need to drive your SQL query from Table C.
The query below displays the updated timestamp column from table A.
Since it is a one-to-many in the direction of tables A --> B --> C
You will inevitably end-up with a lot of rows in table C - all with the same timestamp.
SELECT c.*, a1.update_timestamp
FROM table_c c, table_b b, table_a a1
WHERE c.join_column = b.join_column
AND b.join_column = a1.join_column
AND a1.update_timestamp =
(SELECT max(a2.update_timestamp) FROM table_a a2
WHERE a2.<identifying columns> = a1.<identifying columns>
);
Could someone please verify whether inner join is valid with UPDATE statment in PL SQL?
e.g.
Update table t
set t.value='value'
from tableb b inner join
on t.id=b.id
inner join tablec c on
c.id=b.id
inner join tabled d on
d.id=c.id
where d.key=1
This synthax won't work in Oracle SQL.
In Oracle you can update a join if the tables are "key-preserved", ie:
UPDATE (SELECT a.val_a, b.val_b
FROM table a
JOIN table b ON a.b_pk = b.b_pk)
SET val_a = val_b
Assuming that b_pk is the primary key of b, here the join is updateable because for each row of A there is at most one row from B, therefore the update is deterministic.
In your case since the updated value doesn't depend upon another table you could use a simple update with an EXIST condition, something like this:
UPDATE mytable t
SET t.VALUE = 'value'
WHERE EXISTS
(SELECT NULL
FROM tableb b
INNER JOIN tablec c ON c.id = b.id
INNER JOIN tabled d ON d.id = c.id
WHERE t.id = b.id
AND d.key = 1)
update t T
set T.value = 'value'
where T.id in (select id from t T2, b B, c C, d D
where T2.id=B.id and B.id=C.id and C.id=D.id and D.key=1)
-- t is the table name, T is the variable used to reffer to this table