Let's say you want do something along the following lines:
SELECT CASE
WHEN (SELECT COUNT(id) FROM table WHERE column2 = 4) > 0
THEN 1 ELSE 0 END
Basically just return 1 when there's one or more rows in the table, 0 otherwise. There has to be a grammatically correct way to do this. What might it be? Thanks!
Question: return 1 when there's one or more rows in the table, 0 otherwise:
In this case, there is no need for COUNT. Instead, use EXISTS, which rather than counting all records will return as soon as any is found, which performs much better:
SELECT CASE
WHEN EXISTS (SELECT 1 FROM table WHERE column2 = 4)
THEN 1
ELSE 0
END
Mahmoud Gammal posted an answer with an interesting approach. Unfortunately the answer was deleted due to the fact that it returned the count of records instead of just 1. This can be fixed using the sign function, leading to this more compact solution:
SELECT sign(count(*)) FROM table WHERE column2 = 4
I posted this because I find it an interesting approach. In production I'd usually end up with something close to RedFilter's answer.
You could do this:
SELECT CASE WHEN COUNT(ID) >=1 THEN 1 WHEN COUNT (ID) <1 THEN 0 END FROM table WHERE Column2=4
Reference:
http://msdn.microsoft.com/en-us/library/ms181765.aspx
Related
I need your help with this query.
My table CSO_EMP_ORG_DPM_VIE has a column with different keys. Column name is EXT_KEY.
When I receive the same key number in EXT_KEY, I want the SQL code to count the duplicates using this query:
select EXT_KEY
from CSO_EMP_ORG_DPM_VIE
group by EXT_KEY
having count(*) > 1
This is working so far, but when it has no duplicate keys (numbers) in the column, I want it to generate it with 0 zero, and not nothing.
My expected result is; when two keys are the same I want to generate a 1. When no keys are the same, I want to generate an 0. Right now i got no result at all like in the screenshot.
How can I fix this SQL query accordingly?
Thank you in advance.
Use a CASE expression like this:
SELECT EXT_KEY,
CASE WHEN COUNT(*) > 1 THEN 1 ELSE 0 END flag
FROM CSO_EMP_ORG_DPM_VIE
GROUP by EXT_KEY
or if you want 1 result for the table:
SELECT CASE WHEN COUNT(EXT_KEY) > COUNT(DISTINCT EXT_KEY) THEN 1 ELSE 0 END flag
FROM CSO_EMP_ORG_DPM_VIE
It's not blindingly obvious as to what you are asking for. To that end, this query gives a 1/0 result based on having a count greater than 0 for each key...
SELECT
p.EXT_KEY,
EXT_KEY_RESULT = ISNULL((SELECT 1
FROM CSO_EMP_ORG_DPM_VIE c
WHERE c.EXT_KEY = p.EXT_KEY
HAVING COUNT(EXT_KEY) > 0), 0)
FROM
CSO_EMP_ORG_DPM_VIE p
Alternatively, if you are looking to count each of the keys, you could try...
SELECT EXT_KEY, COUNT(EXT_KEY)
FROM CSO_EMP_ORG_DPM_VIE
GROUP BY EXT_KEY
It's always good practice to specify a particular field in the COUNT aggregate, particularly the primary key, as it's faster to reference.
You really need to give us an expected result for your requirements and be very clear about your expectations.
SELECT CASE WHEN COUNT(EXT_KEY) > 0 THEN 1 ELSE 0 AS dupes
FROM CSO_EMP_ORG_DPM_VIE
PLEASE NOTE: Credit here to forpas for providing a smoother answer which I have borrowed.
I have query which running fine and its doing two types of work, COUNT and SUM.
Something like
select
id,
Count (contracts) as countcontracts,
count(something1),
count(something1),
count(something1),
sum(cost) as sumCost
from
table
group by
id
My problem is: if there is no contract for a given ID, it will return 0 for COUNT and Null for SUM. I want to see null instead of 0
I was thinking about case when Count (contracts) = 0 then null else Count (contracts) end but I don't want to do it this way because I have more than 12 count positions in query and its prepossessing big amount of records so I think it may slow down query performance.
Is there any other ways to replace 0 with NULL?
Try this:
select NULLIF ( Count(something) , 0)
Here are three methods:
1. (case when count(contracts) > 0 then count(contracts) end) as countcontracts
2. sum(case when contracts is not null then 1 end) as countcontracts
3. nullif(count(contracts), 0)
All three of these require writing more complicated expressions. However, this really isn't that difficult. Just copy the line multiple times, and change the name of the variable on each one. Or, take the current query, put it into a spreadsheet and use spreadsheet functions to make the transformation. Then copy the function down. (Spreadsheets are really good code generators for repeated lines of code.)
I am writing a search routine with a ranking algorithm and would like to get this in one pass.
My Ideal query would be something like this....
select *, (select top 1 wordposition
from wordpositions
where recordid=items.pk_itemid and wordid=79588 and nextwordid=64502
) as WordPos,
case when WordPos<11 then 1 else case WordPos<50 then 2 else case WordPos<100 then 3 else 4 end end end end as rank
from items
Is it possible to use WordPos in a case right there? It's generating an error on me , Invalid column name 'WordPos'.
I know I can redo the subquery for each case but I think it would actually re-run the case wouldn't it?
For example:
select *, case when (select top 1 wordposition from wordpositions where recordid=items.pk_itemid and wordid=79588 and nextwordid=64502)<11 then 1 else case (select top 1 wordposition from wordpositions where recordid=items.pk_itemid and wordid=79588 and nextwordid=64502)<50 then 2 else case (select top 1 wordposition from wordpositions where recordid=items.pk_itemid and wordid=79588 and nextwordid=64502)<100 then 3 else 4 end end end end as rank from items
That works....but is it really re-running the identical query each time?
It's hard to tell from the tests as the first time it runs it's slow but subsequent runs are quick....it's caching...so would that mean that the first time it ran it for the first row, the subsequent three times it would get the result from cache?
Just curious what the best way to do this would be...
Thank you!
Ryan
You can do this using a subquery. I will stick with your SQL Server syntax, even though the question is tagged mysql:
select i.*,
(case when WordPos < 11 then 1
when WordPos < 50 then 2
when WordPos < 100 then 3
else 4
end) as rank
from (select i.*,
(select top 1 wpwordposition
from wordpositions wp
where recordid=i.pk_itemid and wordid=79588 and nextwordid=64502
) as WordPos
from items i
) i;
This also simplifies the case statement. You do not need nested case statements to handle multiple conditions, just multiple where clauses.
No. Identifiers introduced in the output clause (the fact that it comes from a sub-query is irrelevant) cannot be used within the same SELECT statement.
Here are some solutions:
Rewrite the query using a JOIN1, This will eliminate the issue entirely and fits well with RA.
Wrap the entire SELECT with the sub-query within another SELECT with the case. The outer select can access identifiers introduced by the inner SELECT's output clause.
Use a CTE (if SQL Server). This is similar to #2 in that it allows an identifier to be introduced.
While "re-writing" the sub-query for each case is very messy it should still result in an equivalent plan - but view the query profile! - as the results of the query are non-volatile. As such the equivalent sub-queries can be safely moved by the query planner which should move the sub-query/sub-queries to a JOIN to avoid any "re-running" in the first place.
1 Here is a conversion to use a JOIN, which is my preferred method. (I find that if a query can't be written in terms of a JOIN "easily" then it might be asking for the wrong thing or otherwise be showing issues with schema design.)
select
wp.wordposition as WordPos,
case wp.wordposition .. as Rank
from items i
left join wordpositions wp
on wp.recordid = i.pk_itemid
where wp.wordid = 79588
and wp.nextwordid = 64502
I've made assumptions about the multiplicity here (i.e. that wordid is unique) which should be verified. If this multiplicity is not valid and not correctable otherwise (and you're indeed using SQL Server), then I'd recommend using ROW_NUMBER() and a CTE.
Ok, so I'm trying to select an amount of rows from a column that holds the value 3, but only if there are no rows containing 10 or 4, if there are rows containing 10 or 4 I only want to show those.
What would be a good syntax to do that? So far I've been attempting a CASE WHEN statement, but I can't seem to figure it out.
Any help would be greatly appreciated.
(My database is in an MS SQL 2008 server)
Use a union all:
select
// columns
from YourTable
where YourColumn = 3 and not exists (
select 1 from YourTable where YourColumn = 10 or YourColumn = 4)
union all
select
// columns
from YourTable
where YourColumn = 10 or YourColumn = 4
FYI: Orginal question title was "SQL CASE WHEN NULL - question"
CASE WHEN YourColumn IS NULL THEN x ELSE y END
Since there is nothing that compares to NULL and returns true (not even NULL itself), you cant't do
CASE YourColumn WHEN NULL THEN x ELSE y END
only
CASE ISNULL(YourColumn, '') WHEN '' THEN x ELSE y END
but then you lose the ability to differentiate between NULL and the (in this example) empty string.
Depending on the size of your table and its indexes, it may be more efficient to calculate which values you want before the query
declare #UseThree as bit = 1;
if exists (select 1 from testtable where rowval in (10,4))
set #UseThree = 0;
select COUNT(*)
from testtable
where (#UseThree = 1 AND rowval=3)
OR
(#UseThree = 0 AND rowval in (10,4))
The simplest solution would be to do this in two queries:
SELECT ... FROM YourTable WHERE SomeColumn IN (10,4)
If and only if the above query yields no results, then run the second query:
SELECT ... FROM YourTable WHERE SomeColumn = 3
Running two queries may seem "inelegant" but it has advantages:
It's easy to code
It's easy to debug
It often has better performance than a very complex solution
It's easy to understand for a programmer who has to maintain the code after you.
Running two queries may seem like it has extra overhead, but also consider that you won't run the second query every time -- only if the first query has an empty result. If you use an expensive single-query solution, remember that it will incur that expense every time.
I'm building a query with a GROUP BY clause that needs the ability to count records based only on a certain condition (e.g. count only records where a certain column value is equal to 1).
SELECT UID,
COUNT(UID) AS TotalRecords,
SUM(ContractDollars) AS ContractDollars,
(COUNTIF(MyColumn, 1) / COUNT(UID) * 100) -- Get the average of all records that are 1
FROM dbo.AD_CurrentView
GROUP BY UID
HAVING SUM(ContractDollars) >= 500000
The COUNTIF() line obviously fails since there is no native SQL function called COUNTIF, but the idea here is to determine the percentage of all rows that have the value '1' for MyColumn.
Any thoughts on how to properly implement this in a MS SQL 2005 environment?
You could use a SUM (not COUNT!) combined with a CASE statement, like this:
SELECT SUM(CASE WHEN myColumn=1 THEN 1 ELSE 0 END)
FROM AD_CurrentView
Note: in my own test NULLs were not an issue, though this can be environment dependent. You could handle nulls such as:
SELECT SUM(CASE WHEN ISNULL(myColumn,0)=1 THEN 1 ELSE 0 END)
FROM AD_CurrentView
I usually do what Josh recommended, but brainstormed and tested a slightly hokey alternative that I felt like sharing.
You can take advantage of the fact that COUNT(ColumnName) doesn't count NULLs, and use something like this:
SELECT COUNT(NULLIF(0, myColumn))
FROM AD_CurrentView
NULLIF - returns NULL if the two passed in values are the same.
Advantage: Expresses your intent to COUNT rows instead of having the SUM() notation.
Disadvantage: Not as clear how it is working ("magic" is usually bad).
I would use this syntax. It achives the same as Josh and Chris's suggestions, but with the advantage it is ANSI complient and not tied to a particular database vendor.
select count(case when myColumn = 1 then 1 else null end)
from AD_CurrentView
How about
SELECT id, COUNT(IF status=42 THEN 1 ENDIF) AS cnt
FROM table
GROUP BY table
Shorter than CASE :)
Works because COUNT() doesn't count null values, and IF/CASE return null when condition is not met and there is no ELSE.
I think it's better than using SUM().
Adding on to Josh's answer,
SELECT COUNT(CASE WHEN myColumn=1 THEN AD_CurrentView.PrimaryKeyColumn ELSE NULL END)
FROM AD_CurrentView
Worked well for me (in SQL Server 2012) without changing the 'count' to a 'sum' and the same logic is portable to other 'conditional aggregates'. E.g., summing based on a condition:
SELECT SUM(CASE WHEN myColumn=1 THEN AD_CurrentView.NumberColumn ELSE 0 END)
FROM AD_CurrentView
It's 2022 and latest SQL Server still doesn't have COUNTIF (along with regex!). Here's what I use:
-- Count if MyColumn = 42
SELECT SUM(IIF(MyColumn = 42, 1, 0))
FROM MyTable
IIF is a shortcut for CASE WHEN MyColumn = 42 THEN 1 ELSE 0 END.
Not product-specific, but the SQL standard provides
SELECT COUNT() FILTER WHERE <condition-1>,
COUNT() FILTER WHERE <condition-2>, ...
FROM ...
for this purpose. Or something that closely resembles it, I don't know off the top of my hat.
And of course vendors will prefer to stick with their proprietary solutions.
Why not like this?
SELECT count(1)
FROM AD_CurrentView
WHERE myColumn=1
I had to use COUNTIF() in my case as part of my SELECT columns AND to mimic a % of the number of times each item appeared in my results.
So I used this...
SELECT COL1, COL2, ... ETC
(1 / SELECT a.vcount
FROM (SELECT vm2.visit_id, count(*) AS vcount
FROM dbo.visitmanifests AS vm2
WHERE vm2.inactive = 0 AND vm2.visit_id = vm.Visit_ID
GROUP BY vm2.visit_id) AS a)) AS [No of Visits],
COL xyz
FROM etc etc
Of course you will need to format the result according to your display requirements.
SELECT COALESCE(IF(myColumn = 1,COUNT(DISTINCT NumberColumn),NULL),0) column1,
COALESCE(CASE WHEN myColumn = 1 THEN COUNT(DISTINCT NumberColumn) ELSE NULL END,0) AS column2
FROM AD_CurrentView