I have two tables, one with orders and another with order comments. I want to join these two tables. They are joined on a column "EID" which exists in both tables. I want all orders. I also want to see all comments with only certain criteria AND all other comments should be set to null. How do I go about this?
Orders Table
Order_Number
1
2
3
4
Comments Table
Comments
Cancelled On
Ordered On
Cancelled On
Cancelled On
In this example I would like to see for my results:
Order_Number | Comments
1 | Cancelled On
2 | Null
3 | Cancelled On
4 | Cancelled On
Thanks!
This seems like a rather trivial left join.
select o.order_number, c.comments
from orders o
left join comments c
on o.eid = c.eid
and (here goes your criteria for comments)
Tested on Oracle, there might be subtle syntax differences for other DB engines.
It depends on one condition:
Are you trying to SET the other comments to null? (replace the values in the table)
or
Are you trying to DISPLAY the other comments as null? (dont display them)
If you want to change the values in the table use
UPDATE `table` SET `column` = null WHERE condition;
otherwise use:
SELECT column FROM table JOIN othertable WHERE condition;
Related
My update query checks whether the column “Houses” is null in any of the rows in my source table by joining the id between the target & source table (check query one). The column Houses being null in this case indicates that the row has expired; thus, I need to expire the row id in my target table and set the expired date. The query works fine, but I was wondering if it can be improved; I'm new to SQL, so I don't know if using two joins is the best way to accomplish the result I want. My update query will later be used against millions of rows. No columns has been indexed yet.
Query:
(Query one)
Update t
set valid_date = GETDATE()
From Target T
JOIN SOURCE S ON S.ID = T.ID
LEFT JOIN SOURCE S2 ON S2.Houses = t.Houses
WHERE S2.Houses is null
Target:
ID
namn
middlename
Houses
date
1
demo
hello
2
null
2
demo2
test
4
null
3
demo3
test1
5
null
Source:
ID
namn
middlename
Houses
1
demo
hello
null
3
demo
world
null
Expected output after running update query :
ID
namn
middlename
Houses
date
1
demo
hello
2
2022-12-06
2
demo2
test
4
null
3
demo3
test1
5
2022-12-06
I would recommend exists:
update t
set valid_date = getdate()
from target t
where exists (select 1 from source s where s.id = t.id and s.houses is null)
Note that your original query does not exactly do what you want. It cannot distinguish source rows that do not exist from source rows that exist and whose houses column is null. In your example, it would update row 2, which is not what you seem to want. You would need an INNER JOIN instead of the LEFT JOIN.
With EXISTS, you want an index on source(id, houses) so the subquery can execute efficiently against target rows. This index is probably worthwhile for the the JOIN as well.
I don't see why you'd need to join on the column houses at all.
Find all rows in source that have value NULL in the column houses.
Then update all rows in target that have the IDs of the source rows.
I prefer to write these kind of complex updates using CTEs. It looks more readable to me.
WITH
CTE
AS
(
SELECT
Target.ID
,Target.Date
FROM
Source
INNER JOIN Target ON Target.ID = Source.ID
WHERE Source.Houses IS NULL
)
UPDATE CTE
SET Date = GETDATE();
To efficiently find rows in source that have value NULL in the column houses you should create an index, something like this:
CREATE INDEX IX_Houses ON Source
(
Houses
);
I assume that ID is a primary key with a clustered unique index, so ID would be included in the IX_Houses index implicitly.
I can not understand what I am doing wrong.
My array:
ps_product
id_product
active
1
1
2
1
and
ps_product_sync
id_product
status
1
0
2
1
and my SQL code
SELECT pr_product.id_product, pr_product.active
FROM pr_product, pr_product_sync
WHERE pr_product.active = pr_product_sync.status
I get a result like this:
id_product
status
2
1
2
1
2
1
...
..
24 rows
I try the same with inner but result is the same, I don't have duplicates in the arrays... I don't understand why I get one row 24 times
PS. all tables looks good before posting/saving
If you query two tables and include both in the FROM clause, you create a Cartesian product of these tables. In other words, if one table has 4 rows and the other 6 rows, the result is 24 rows.
It is better to create an INNER JOIN using the key of the first table and the foreign key of the second table.
Change your query accordingly
SELECT pr_product.id_product, pr_product.active
FROM pr_product
INNER JOIN pr_product_sync
ON pr_product.id_product = ps_product_sync.id_product
WHERE pr_product.active = pr_product_sync.status
Of course, you could also compare the Keys in the WHERE clause or eliminate duplicates using DISTINCT. IMHO the most understandable solution is an INNER JOIN.
I hope this solves your problem.
Missing the primary key join.
Add:
WHERE
pr_product.id_product=pr_product_sync.id_product
AND pr_product.active=pr_product_sync.status
There are two tables Table A and Table B. These contains the same columns cost and item. The Table B contains the list of items and their corresponding costs whereas the Table A contains only the list of items.
Now we need to check the items of Table A, if they are present in the Table B then the corresponging item cost should be assigned to the item's cost in Table A.
Can someone help me out by writing a query for this.
Consider the tables as shown:
Table A:
item cost
-------------
pen null
book null
watch null
Table B:
item cost
-------------
watch 1000
book 50
Expected output
Table A:
item cost
pen 0
book 50
watch 1000
Just add a foreign key (primary key of table A) in the Table B as you can say table A ID then add a join(right join may be) in the query to get or assign the prices respective items.
join be like
SELECT item, cost
FROM tablename a
RIGHT JOIN tablename b ON a.item= b.item;
Edit:
Just edit this table name ,now run it.
I would structure the update like this:
with cost_data as (
select
item,
max (cost) filter (where item = 'watch') as watch,
max (cost) filter (where item = 'book') as book
from table_b
group by item
)
update table_a a
set
watch = c.watch,
book = c.book
from cost_data c
where
a.item = c.item and
(a.watch is distinct from c.watch or
a.book is distinct from c.book)
In essence, I am doing a common table expression to do a poor man's pivot table on the Table B to get the rows into columns. One caveat here -- if there are multiple costs listed for the same item, this may not do what you want, but then you would need to know how to handle that in almost any case.
Then I am doing an "update A from B" against the CTE.
The last part is not critical, per se, but it is helpful -- to limit the query to only execute on rows that need to change. It's best to limit DML if it doesn't need to occur (the best way to optimize something is to not do it).
There are plenty of ways you could do this, if you are taking table b to be the one containing the price then a left outer join would do the trick.
SELECT
table_a.item,
CASE
WHEN table_b.cost IS NULL
THEN 0
ELSE table_b.cost
END as cost
FROM table_a
LEFT OUTER JOIN table_b ON table_a.item = table_b.item
The result also appears to suggest that pen which is not in table b should have a price of 0 (this is bad practice) but for the sake of returning the desired result you will want a case statement to assign a value if it is null.
In order to update the table, as per the comment
update table_a set cost = some_alias.cost
from (
SELECT
table_a.item,
CASE
WHEN table_b.cost IS NULL
THEN 0
ELSE table_b.cost
END as cost
FROM table_a
LEFT OUTER JOIN table_b ON table_a.item = table_b.item
) some_alias
where table_a.item = some_alias.item
I can already hear the groans looking at my title but please bear with me a moment. :)
I have two tables that have a few columns in common and are updated through different means. Given a specific identifier I want to update the first table with values from the second table if the first table is missing some information.
Table A looks something like:
Dept_ID Reviewer Reviewer_Team Reviewer_Code
ACM Null Null Null
EOT Null Null Null
QQQ Joe Joe's Group XYZ
ACM Null Null Null
ZZZ Null Null Null
Table B looks something like:
Dept_ID Reviewer Reviewer_Team Reviewer_Code
AAA Al Al's Group 123
BBB Bob Bob's Group 234
ZZZ Zoe Zoe's Group 567
If Reviewer_Code is Null in Table A we want to find Table A's Dept_ID in Table B, and update Table A's other fields to match Table B. Note that Table A might have multiple records with the same Dept_ID in which case we'd expect them to have the same values updated from Table B.
Sounds easy. Using the above tables as an example there are no matches in Table B, so the ACM and EOT records would not be updated at this step. Table A's ZZZ record though would get updated based on Table B's ZZZ record.
However there's a chance that there would be no matches in Table B. So pretend Table A doesn't have the ZZZ record, just the ACM and EOT that have Nulls.
I'm new to Oracle (coming from SQL Server) so maybe I'm testing this wrong, but what I have is a bunch of queries one after another in a .sql window of Oracle SQL Developer. This seems to work for me just fine normally. When it gets to this query though I get the dreaded "single-row subquery" error.
Here's the query I've tried a few different ways:
UPDATE VchrImpDetailCombined vchr
SET (Reviewer, Reviewer_Team, Reviewer_Code) =
(SELECT DISTINCT b.Reviewer, b.Reviewer_Team, b.Reviewer_Code
FROM GlobPMSDeptIdMapping b
WHERE b.Dept_Id = vchr.Dept_Id)
WHERE vchr.Reviewer_Code IS NULL
AND vchr.Business_L1 = 'CF'
AND vchr.Dept_ID IS NOT NULL;
or
UPDATE VchrImpDetailCombined vchr
SET (Reviewer, Reviewer_Team, Reviewer_Code) =
(SELECT DISTINCT b.Reviewer, b.Reviewer_Team, b.Reviewer_Code
FROM GlobPMSDeptIdMapping b
inner join VchrImpDetailCombined a
on b.Dept_Id = a.Dept_Id
WHERE b.Dept_Id = vchr.Dept_Id)
WHERE vchr.Reviewer_Code IS NULL
AND vchr.Business_L1 = 'CF'
AND vchr.Dept_ID IS NOT NULL;
I've tried a few other things as well such as doing "WHERE EXISTS SELECT blahblah", or "WHERE b.Dept_ID IS NOT NULL", etc.
Now, given my example data above, the subquery should have 0 records, keeping in mind there actually isn't a ZZZ record in Table A like my example, just the ACM and EOT. Table B simply doesn't have records with the matching Dept_ID in Table A. So my expectation would be for a 0 record update and happily moving along to the next query.
When I run these queries in a string of other queries I get the error. If I run the query all by its lonesome I simply get a "3 rows updated" which seems odd that anything is updating considering there should be no matches. But the 3 rows updated would seem to match the 3 ACM and EOT records even though Table B has nothing to update from given the criteria.
I must be missing something obvious, but I just can't seem to grasp it. There's a bajillion of these ORA-01427 questions so I was so sure I could find the answer already out there, but couldn't seem to find it.
Any ideas?
You need to instruct Oracle that it should perform the update only when there are data with which to do so (and I would have expected such to be needed for SQL Server as well, but I'm uncertain). This will overcome that obstacle, at the expense of performing an additional subquery:
UPDATE VchrImpDetailCombined vchr
SET (Reviewer, Reviewer_Team, Reviewer_Code) = (
SELECT b.Reviewer, b.Reviewer_Team, b.Reviewer_Code
FROM GlobPMSDeptIdMapping b
WHERE b.Dept_Id = vchr.Dept_Id
)
WHERE vchr.Reviewer_Code IS NULL
AND vchr.Business_L1 = 'CF'
AND vchr.Dept_ID IN (
SELECT Dept_Id
FROM GlobPMSDeptIdMapping
);
Per my comment on the question, I removed the DISTINCT from the (original) subquery, as it's either unneeded or ineffective.
Sorry if this is a basic question. I'm fairly new to SQL, so I guess I'm just missing the name of the concept to search for.
Quick overview.
First table (items):
ID | name
-------------
1 | abc
2 | def
3 | ghi
4 | jkl
Second table (pairs):
ID | FirstMember | SecondMember Virtual column (pair name)
-------------------------------------
1 | 2 | 3 defghi
2 | 1 | 4 abcjkl
I'm trying to build the virtual column shown in the second table
It could be built at the time any entry is made in the second table, but if done that way, the data in that column would get wrong any time one of the items in the first table is renamed.
I also understand that I can build that column any time I need it (in either plain requests or stored procedures), but that would lead to code duplication, since the second table can be involved in multiple different requests.
So is there a way to define a "virtual" column, that could be accessed as a normal column, but whose content is built dynamically?
Thanks.
Edit: this is on MsSql 2008, but an engine-agnostic solution would be preferred.
Edit: the example above was oversimplified in multiple ways - the major one being that the virtual column content isn't a straight concatenation of both names, but something more complex, depending on the content of columns I didn't described. Still, you've provided multiple paths that seems promising - I'll be back. Thanks.
You need to join the items table twice:
select p.id,
p.firstMember,
p.secondMember,
i1.name||i2.name as pair_name
from pairs as p
join items as i1 on p.FirstMember = i1.id
join items as i2 on p.SecondMember = i2.id;
Then put this into a view and you have your "virtual column". You would simply query the view instead of the actual pairs table wherever you need the pair_name column.
Note that the above uses inner joins, if your "FirstMember" and "SecondMember" columns might be null, you probably want to use an outer join instead.
You can use a view, which creates a table-like object from a query result, such as the one with a_horse_with_no_name provided.
CREATE VIEW pair_names AS
SELECT p.id,
p.firstMember,
p.secondMember,
CONCAT(i1.name, i2.name) AS pair_name
FROM pairs AS p
JOIN items AS i1 ON p.FirstMember = i1.id
JOIN items AS i2 ON p.SecondMember = i2.id;
Then to query the results just do:
SELECT id, pair_name FROM pair_names;
You could create a view for your 'virtual column', if you wanted to, like so:
CREATE VIEW aView AS
SELECT
p.ID,
p.FirstMember,
p.SecondMember,
a.name + b.name as 'PairName'
FROM
pairs p
LEFT JOIN
items a
ON
p.FirstMember = a.ID
LEFT JOIN
items b
ON
p.SecondMember = b.ID
Edit:
Or, of course, you could just use a similar select statement every time.
When selecting from tables you can name the results of a column using AS.
SELECT st.ID, st.FirstMember, st.SecondMember, ft1.Name + ft2.Name AS PairName
FROM Second_Table st
JOIN First_Table ft1 ON st.FirstMember = ft1.ID
JOIN First_Table ft2 ON st.SecondMember = ft2.ID
Should give you something like what you are after.