I have a query inside a stored procedure that sums some values inside a table:
SELECT SUM(columnA) FROM my_table WHERE columnB = 1 INTO res;
After this select I subtract res value with an integer retrieved by another query and return the result. If WHERE clause is verified, all works fine. But if it's not, all my function returns is an empty column (maybe because I try to subtract a integer with an empty value).
How can I make my query return zero if the WHERE clause is not satisfied?
You could:
SELECT COALESCE(SUM(columnA), 0) FROM my_table WHERE columnB = 1
INTO res;
This happens to work, because your query has an aggregate function and consequently always returns a row, even if nothing is found in the underlying table.
Plain queries without aggregate would return no row in such a case. COALESCE would never be called and couldn't save you. While dealing with a single column we can wrap the whole query instead:
SELECT COALESCE( (SELECT columnA FROM my_table WHERE ID = 1), 0)
INTO res;
Works for your original query as well:
SELECT COALESCE( (SELECT SUM(columnA) FROM my_table WHERE columnB = 1), 0)
INTO res;
More about COALESCE() in the manual.
More about aggregate functions in the manual.
More alternatives in this later post:
How to return a value from a function if no value is found
I'm not familiar with postgresql, but in SQL Server or Oracle, using a subquery would work like below (in Oracle, the SELECT 0 would be SELECT 0 FROM DUAL)
SELECT SUM(sub.value)
FROM
(
SELECT SUM(columnA) as value FROM my_table
WHERE columnB = 1
UNION
SELECT 0 as value
) sub
Maybe this would work for postgresql too?
You can also try: (I tried this and it worked for me)
SELECT ISNULL((SELECT SUM(columnA) FROM my_table WHERE columnB = 1),0)) INTO res;
You can use exists clause.
IF EXISTS(SELECT FROM my_table WHERE columnB = 1)
THEN
res := SUM(columnA);
ELSE
res := 0
END IF;
Related
I have the following SQL Query :
(SELECT ROUND(SUM(NBTOSUM)/1000000,1) FROM MyTable t2 WHERE t2.ELEMNAME IN ('A','B','C'))
Which works fine.
But Where there is no 'A','B','C' the result of the select is (null)
So to handle it, I did the following :
(SELECT COALESCE(ROUND(SUM(NBTOSUM)/1000000,1),0) FROM MyTable t2 WHERE t2.ELEMNAME IN ('A','B','C'))
And also try :
(SELECT
CASE
WHEN SUM(NBTOSUM)/1000000 IS NULL THEN 0
ELSE ROUND(SUM(NBTOSUM)/1000000,1)
END
FROM MyTable t2 WHERE t2.ELEMNAME IN ('A','B','C'))
But both keep returning null
What am I doing wrong ?
Move the WHERE restrictions to the CASE expression as well:
SELECT ROUND(SUM(CASE WHEN t2.ELEMNAME IN ('A','B','C')
THEN NBTOSUM ELSE 0 END) / 1000000, 1)
FROM MyTable t2;
Note that this trick solves the null problem and also avoids the need for an ugly COALESCE() call.
Your code should work as the SUM aggregation function will generate a single row of output regardless of whether the number of input rows is zero or non-zero. If there are no input rows or the values are all NULL then the output of the SUM will be NULL and then COALESCE would work.
Since you claim it does not then that suggests that there is something else going on in your query that you have not shared in the question.
You have braces around your statement suggesting that you are using it as part of a larger statement. If so, you can try moving the COALESCE to the outer query:
SELECT COALESCE(
(
SELECT ROUND(SUM(NBTOSUM)/1000000,1)
FROM MyTable
WHERE ELEMNAME IN ('A','B','C')
),
0
)
FROM your_outer_query;
That might fix the problem if you are somehow correlating to an outer query but your question makes no mention of that.
fiddle
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 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
How do I do to select all or nothing using SQL, following the condition: If any tuple has a column with the value 1 it must return empty, however if all have the value 0 it return all tuples.
You can do it like this:
SELECT *
FROM MyTable
WHERE (SELECT COUNT(*) FROM MyTable t WHERE t.MyColumn=1)=0
The condition evaluates to true or false for all rows; if any row has 1 in it, no rows would be returned.
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.