How can I use CASE statement or IF statement in WHERE clause ?
I am trying to apply a check on the basis of COUNT
SELECT * FROM sometable
WHERE CASE WHEN (SELECT COUNT(*) FROM sometable s WHERE SP = 2 AND sometable.id = s.id) > 2 THEN sometable.SP IS NOT NULL END
So basically if the count of rows is more than 1 it should apply IS NOT NULL condition else it should not.
Your logic suggests something like:
SELECT s.*
FROM (SELECT s.*,
SUM(CASE WHEN sp = 2 THEN 1 ELSE 0 END) OVER (PARTITION BY id) as cnt_2
FROM sometable s
) s
WHERE cnt_2 <= 2 OR s.sp is not null;
That seems equivalent. The logic doesn't seem particularly useful though.
Related
I want to check whether these customers have LEAD action or SELL action which both stay in another tables. However, It takes like forever to finish it.
create table ct_nguyendang.visitor
as
select user_id, updated_at::date,
case
when user_id in (select distinct d_visitor_id from xiti.lead_detail) then 'lead'
else 'None'
end as lead_action,
case
when user_id in (select distinct account_id from ct_nguyendang.daily_listor) then 'sell'
else 'None'
end as sell_action
I think you can use union all and aggregation:
select user_id, max(is_lead) as has_lead, max(is_sale) as has_sale
from ((select d_visitor_id as user_id, 1 as is_lead, 0 as is_sale
from xiti.lead_detail
) union all
(select account_id, 0, 1
from ct_nguyendang.daily_listor
)
) ls
group by user_id;
If you have a table of users, then you can use correlated subqueries:
select u.*,
(case when exists (select 1
from xiti.lead_detail l
where u.user_id = l.d_visitor_id
)
then 1 else 0
end) as has_lead,
(case when exists (select 1
from ct_nguyendang.daily_listor s
where u.user_id = s.account_id
)
then 1 else 0
end) as has_sale
from users u;
Note that I prefer using 1 for "true" and 0 for "false". Of course, you can use string values if you prefer.
To optimize this query, you want indexes on xiti.lead_detail(d_visitor_id) and ct_nguyendang.daily_listor(account_id).
I have three tables A,B and C. I have to detect if any of them have zero rows. As soon as any table with zero row is detected, I do not need to check other ones.
So, one way is I execute three queries separately and after each query I check the number of returned rows. If its non-zero then only I execute the query of next table.
Second way is I write a single query using case-when, something like
select case
when (select count(*) from A = 0)
then 1
else (
select case
when (select count(*) from B = 0)
then 1
else (
select case
when (select count(*) from B = 0)
then 1
else 0
)
)
end as matchResult;
The second method requires lesser code as I have to write a single query and db will do the comparison for me.
My question is whether its overkilling or can I further optimize the query?
EDIT
On further study, I realise that the query above is wrong. However, I can simply do it as
select case
when (select count(*) from A) = 0 and
(select count(*) from B) = 0 and
(select count(*) from C) = 0
then 1
else 0
end as matchResult;
and if I am not wrong, and conditions are checked from left to right and if any one is false, conditions to the right are not checked.
Please confirm this point.
Count is kind of expensive
select 1
where not exits (select * from a)
or not exits (select * from b)
or not exits (select * from c)
One query with three resutls:
select (select count(*) from A) as Acount,
(select count(*) from B) as Bcount,
(select count(*) from C) as Ccount
This instead gives name of the fitst table that is empty:
select case
when (select count(*) from A)=0 then 'A'
when (select count(*) from B)=0 then 'B'
when (select count(*) from C)=0 then 'C'
else 'ops, all have records' -- remove this to have a null
end as first_empty_table
I was wondering if something like this was possible in SQL :
select (
(select count(*) from T) = (select count(*) from T t where t.something = thing)
)
This is probably very far from the actual SQL if it is possible, I don't write database requests so often.
How could I get the result of my comparison with a single request ? Basically, if I had no time, I would just make two requests and compare the results in Java (boooooo !! I know).
Although your query should work, the following is probably faster because only a single query is needed
select total_count = thing_count
from (
select count(*) as total_count,
sum(case when something = 42 then 1 end) as thing_count
from t
) t
The above is ANSI SQL and should work in any DBMS supporting a real boolean type. In Oracle you would need to use an expression in the outer select:
select case when total_count = thing_count then 1 else 0 end
from (
select count(*) as total_count,
sum(case when something = 42 then 1 end) as thing_count
from t
) t
I would write your query like this:
SELECT (CASE WHEN (select count(*) from T) = (select count(*) from T t where t.something = thing) THEN 1 ELSE 0 END)
However, if the first T is the same as the second T then what you actually want to check is if there are any records where t.something <> thing .. right ?
In that case you could simply do :
SELECT (CASE WHEN EXISTS (select * from T t where t.something != thing) THEN 1 ELSE 0 END)
I have the following SQL (example):
SET #Return_Value = = (SELECT Top 1
(CASE WHEN .... THEN ColumValue1 ELSE ColumValue2 END)
FROM TableA WHERE (Lots of AND Statements)
AND
(
(bla1)
OR
(bla2)
OR
(bla3)
)
The bla1, etc are logic to retrieve colum values from TableA. How can I return the values from bla1 if they were found without executing bla2 or bla3 because those might overwrite what I'm looking for? In other words I only want to execute OR statements if the previous one didn't find data, all this within a function.
You can use a case expression as :
SET #Return_Value = (SELECT Top 1
(CASE WHEN .... THEN ColumValue1 ELSE ColumValue2 END)
FROM TableA WHERE (Lots of AND Statements)
AND
( 1 = case when condition1 then 1
case when condition2 then 1
case when condition3 then 1
end
);
you can use order by, like
select Top 1
CASE WHEN .... THEN ColumValue1 ELSE ColumValue2 END
FROM TableA
WHERE
(Lots of AND Statements) AND
(
(bla1) OR
(bla2) OR
(bla3)
)
order by
case
when (bla1) then 1
when (bla2) then 2
when (bla3) then 3
else 999
end
Or you can try to simplify it (but you have to check performance):
select Top 1
CASE WHEN .... THEN ColumValue1 ELSE ColumValue2 END
FROM TableA
outer apply (
select
case
when (bla1) then 1
when (bla2) then 2
when (bla3) then 3
end as T
) as C
WHERE
(Lots of AND Statements) and
C.T is not null
order by C.T
or, for example, you can use union, something like this:
with cte as (
select Top 1
CASE WHEN .... THEN ColumValue1 ELSE ColumValue2 END as data
FROM TableA
WHERE
(Lots of AND Statements)
), cte2 as (
select top 1 data, 1 as c from cte where (bla1)
union all
select top 1 data, 2 as c from cte where (bla2)
union all
select top 1 data, 3 as c from cte where (bla3)
)
select top 1 data
from cte2
order by c
How can I improve the SQL query below (SQL Server 2008)? I want to try to avoid sub-selects, and I'm using a couple of them to produce results like this
StateId TotalCount SFRCount OtherCount
---------------------------------------------------------
AZ 102 50 52
CA 2931 2750 181
etc...
SELECT
StateId,
COUNT(*) AS TotalCount,
(SELECT COUNT(*) AS Expr1 FROM Property AS P2
WHERE (PropertyTypeId = 1) AND (StateId = P.StateId)) AS SFRCount,
(SELECT COUNT(*) AS Expr1 FROM Property AS P3
WHERE (PropertyTypeId <> 1) AND (StateId = P.StateId)) AS OtherCount
FROM Property AS P
GROUP BY StateId
HAVING (COUNT(*) > 99)
ORDER BY StateId
This may work the same, hard to test without data
SELECT
StateId,
COUNT(*) AS TotalCount,
SUM(CASE WHEN PropertyTypeId = 1 THEN 1 ELSE 0 END) as SFRCount,
SUM(CASE WHEN PropertyTypeId <> 1 THEN 1 ELSE 0 END) as OtherCount
FROM Property AS P
GROUP BY StateId
HAVING (COUNT(*) > 99)
ORDER BY StateId
Your alternative is a single self-join of Property using your WHERE conditions as a join parameter. The OtherCount can be derived by subtracting the TotalCount - SFRCount in a derived query.
Another alternative would be to use the PIVOT function like this:
SELECT StateID, [1] + [2] AS TotalCount, [1] AS SFRCount, [2] AS OtherCount
FROM Property
PIVOT ( COUNT(PropertyTypeID)
FOR PropertyTypeID IN ([1],[2])
) AS pvt
WHERE [1] + [2] > 99
You would need to add an entry for each property type which could be daunting but it is another alternative. Scott has a great answer.
If PropertyTypeId is not null then you could do this with a single join. Count is faster than Sum. But is Count plus Join faster than Sum. The test case below mimics your data. docSVsys has 800,000 rows and there are about 300 unique values for caseID. The Count plus Join in this test case is slightly faster than the Sum. But if I remove the with (nolock) then Sum is about 1/4 faster. You would need to test with your data.
select GETDATE()
go;
select caseID, COUNT(*) as Ttl,
SUM(CASE WHEN mimeType = 'message/rfc822' THEN 1 ELSE 0 END) as SFRCount,
SUM(CASE WHEN mimeType <> 'message/rfc822' THEN 1 ELSE 0 END) as OtherCount,
COUNT(*) - SUM(CASE WHEN mimeType = 'message/rfc822' THEN 1 ELSE 0 END) as OtherCount2
from docSVsys with (nolock)
group by caseID
having COUNT(*) > 1000
select GETDATE()
go;
select docSVsys.caseID, COUNT(*) as Ttl
, COUNT(primaryCount.sID) as priCount
, COUNT(*) - COUNT(primaryCount.sID) as otherCount
from docSVsys with (nolock)
left outer join docSVsys as primaryCount with (nolock)
on primaryCount.sID = docSVsys.sID
and primaryCount.mimeType = 'message/rfc822'
group by docSVsys.caseID
having COUNT(*) > 1000
select GETDATE()
go;