I have two queries, first is a check if value exists in table1, if yes - I'm updating a value in table2, otherwise I return 0 as a count of found values.
It happens really often and I wish I could do that with one query. How would the query look like then?
Maybe you can try something like this. A RETURNING clause will return rows if at least one row was updated in the with clause. It is then verified by an exists check in the select part.
with upd as
(
update table2 t2 set col = 'value4'
where id = ? and exists ( select 1 from table1 t1 where id = ? ) returning *
)
select exists ( select 1 from upd ) :: int as "updated";
This query when run will return 0 ( integer equivalent of boolean false ) when no rows exist and 1 when at least one row was updated.
DEMO
You can join table1 & table2 and then update the value from table2 with table1.
Related
What is better approach to check existence of an object in database?
select count(id) as count from my_table where name="searchedName";
OR
select id from my_table where name="searchedName";
And then check if count > 0 or the object is not null (ORM logic)
EDIT:
select id to be valid for Oracle.
The idea should be to that we only need to find one record in order to say that such record exists. This can be done with an EXISTS clause in standard SQL.
select exists (select * from mytable where name = 'searchedName');
returns true if the table contains a record with 'searchedName' and false otherwise.
If you want 0 for false and 1 for true instead (e.g. if the DBMS does not support booleans):
select case when exists (select * from mytable where name = 'searchedName')
then 1 else 0 end as does_exist;
You say you want this for Oracle. In Oracle you can use above query, but you'd have to select from the table dual:
select case when exists (select * from mytable where name = 'searchedName')
then 1 else 0 end as does_exist
from dual;
But for Oracle we'd usually use rownum instead:
select count(*) as does_exist
from mytable
where name = 'searchedName'
and rownum = 1; -- to find one record suffices and we'd stop then
This also returns 1 if the table contains a record with 'searchedName' and 0 otherwise. This is a very typical way in Oracle to limit lookups and the query is very readable (in my opinion).
I'd just call:
select id from my_table where name='searchedName';
Making sure there is an index for the name column.
And then check whether or not the result is empty.
Try with IF EXISTS (
if exists (select 1 from my_table where name = "searchedName")
begin
....
end
I have a scenario where I have to search value of column 1 in first table to see whether it matches some value in another table.
This should continue in a loop until the last row on first table has been compared.
No loops needed. You can do this easily as a set based operation using exists()
select *
from FirstTable
where exists (
select 1
from SecondTable
where FirstTable.Column1 = SecondTable.Column1
);
To find the opposite, where the row in the first table does not have a match based on Column1, you can use not exists()
select *
from FirstTable
where not exists (
select 1
from SecondTable
where FirstTable.Column1 = SecondTable.Column1
);
If you want to identify which rows have a match and don't you can use:
select FirstTable.*
, MatchFound = case when x.Column1 is null then 'No' else 'Yes' end
, x.Column1
from FirstTable
outer apply (
select top 1
*
from SecondTable
where FirstTable.Column1 = SecondTable.Column1
) as x
I want to return 0 if there is no record or if the Column1 is null.
select #var = Column1
from myschema.mytable
where Id = #suppliedId;
select isnull(#var, 0);
The above code outputs 0 if if Column1 is null. Or if a row is not found
Whereas I tried to save some keystrokes but it resulted in,
select isnull(Column1, 0)
from myschema.mytable
where Id = #suppliedId;
The above code outputs null if Column1 is null or when there is no row
Any ideas what is wrong here ? Or is there any shorter way of writing the first code ?
You can do
SELECT #var = ISNULL(MAX(Column1), 0)
FROM myschema.mytable
WHERE Id = #suppliedId;
A scalar aggregate always returns a single row even if the underlying query returns zero rows.
Not really saving key strokes, but something like this could help :-)
SELECT TOP 1 tbl.field
FROM
(
SELECT 0 AS inx, 'no record' AS field
--if only one row is possible, than set '1' literally
UNION SELECT ROW_NUMBER() OVER(ORDER BY mytable.orderfield), ISNULL(mytable.Land,'is null')
FROM mytable
WHERE IDENTITY = #suppliedID
) AS tbl
ORDER BY tbl.inx DESC
I am constructing an SQL statement with some parameters. Finally, an SQL statement is created like
"select * from table where column1 = "xyz"".
But I also need the rows which are filtered with this statement. In this case they're rows which are not "xyz" valued in column1. More specifically, I am looking for something like INVERSE(select * from table where ...). Is it possible?
Edit: My bad, I know I can do it with != or operator. Here the case is, select statement may be more complex (with some ANDs and equal, greater operators). Let's assume a table has A,B,C and my SQL statement brings only A as result. But I need B and C while I only have the statement which brings A.
select * from table where column1 != 'xyz' or column1 is null;
If you want the other ones, do it like this:
select * from table where column1 <> "xyz"
column1 <> (differs from) "xyz"
To check if something is no equal you can use <> or even !=
SELECT *
FROM yourTable
WHERE <> 'xyz'
OR
SELECT *
FROM yourTable
WHERE != 'xyz'
Many database vendors support (see list) both versions of the syntax.
If you're retrieving both result sets at about the same time, and just want to process the xyz ones first, you could do:
select *,CASE WHEN column1 = "xyz" THEN 1 ELSE 0 END as xyz from table
order by CASE WHEN column1 = "xyz" THEN 1 ELSE 0 END desc
This will return all of the rows in one result set. Whilst xyz = 1, these were the rows with column1 = 'xyz'.
It was :
"select * from table where rowId NOT IN (select rowId from table where column1 = "xyz")
I needed a unique rowId column to achieve this.
I want to return multiple values from a query in oracle. For ex:
select count(*)
from tablename a
where asofdate='10-nov-2009'
and a.FILENAME in (case
when 1 = 1 then (select distinct filename from tablename
where asofdate='10-nov-2009' and isin is null)
else null
end);
I am getting error: ora 01427 single row subquery returns more than one row
Please advice.
Thanks, Deepak
A CASE statement cannot return more than one value, it is a function working on one value.
It is not required for your statement, this statement should work:
select count(*)
from tablename a
where asofdate='10-nov-2009'
and a.FILENAME in (select distinct filename
from tablename
where asofdate='10-nov-2009'
and isin is null);
Maybe you have another usage scenario in mind? Something like this:
Select *
From aTable
Where in CASE
WHEN Then
WHEN Then
ELSE END
Then using CASE may not be the right scenario. Maybe this helps you in the right direction:
Select *
From aTable
Where <Case1> and column1 in <Subselect1>
Or <Case2> and column1 in <Subselect2>
OR Not (<Case1> Or <Case2>) and column1 in <Subselect3>
But this will probably be quite some work for the optimizer ...
The distinct in your Case statement is attempting to return multiple values when only one is allowed, and your SELECT statement will only return one value in one row currently. If you're trying to get the count of each filename, do
SELECT FileName, Count(*)
FROM tablename
WHERE asofdate='10-nov-2009' and isin is null
GROUP BY FileName
Run this query:
select distinct filename from tablename
where asofdate='10-nov-2009' and isin is null
You'll see that it returns more than a single row which causes the ORA-01427.
For all I can tell, you're looking for something like:
select a.filename, count(*)
from tablename a
where a.asofdate = '10-nov-2009'
and exists (
select *
from tablename b
where b.isin is null
and a.asofdate = '10-nov-2009'
and a.filename = b.filename
)
group by a.filename
This would find the count of filenames for a day, for which there exists at least one row where isin is null.
If you edit your question and add an explanation of what you're looking for, you might get better answers.