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.
Related
I want to return 1 if some number already exists in table and 0 otherwise.
I tried something but it doesn't work:
select
case when 100 in (select distinct id from test) then '1'
else '0'
from test
I want something similar to exists function that already exists in PostgreSQL, but instead of true and false I want 1 or 0.
EXISTS yields a boolean result.
The simple way to achieve what you are asking for is to cast the result to integer:
SELECT (EXISTS (SELECT FROM test WHERE id = 100))::int;
TRUE becomes 1.
FALSE becomes 0.
See:
Return a value if no record is found
Or with UNION ALL / LIMIT 1 (probably slightly faster):
SELECT 1 FROM test WHERE id = 100
UNION ALL
SELECT 0
LIMIT 1;
If a row is found, 1 is returned and Postgres stops execution due to LIMIT 1. Else, 0 is returned.
Disclaimer for the UNION ALL solution: this relies on undocumented behavior that Postgres would execute UNION ALL terms in sequence. This used to be the case until Postgres 11, where Parallel Append was added to Postgres. It's actually still the case (currently Postgres 15) for the given example, as retrieving a single row will never trigger a Parallel Append plan. But it remains undocumented behavior, so you might not want to rely on it. See:
Are results from UNION ALL clauses always appended in order?
If the field you are testing is the Primary Key (or some other unique constraint), then you can simply return the count (which will always be 0 or 1):
SELECT count(*) FROM test WHERE id = 100;
it easy and quick:
SELECT ISNULL((SELECT 1 FROM test WHERE id = 100), 0) res
I have these two tables (the names have been pluralized for the sake of the example):
Table Locations:
idlocation varchar(12)
name varchar(50)
Table Answers:
idlocation varchar(6)
question_number varchar(3)
answer_text1 varchar(300)
answer_text2 varchar(300)
This table can hold answers for multiple locations according a list of numbered questions that repeat on each of them.
What I am trying to do is to add up the values residing in the answer_text1 and answer_text2 columns, for each location available on the Locations table but for only an specific question and then output a value based on the result (1 or 0).
The query goes as follows using a nested table Answers to perform the SUM operation:
select
l.idlocation,
'RESULT' = (
case when (
select
sum(cast(isnull(c.answer_text1,0) as int)) +
sum(cast(isnull(c.answer_text2,0) as int))
from Answers c
where b.idlocation=c.idlocation and c.question_number='05'
) > 0 then
1
else
0
end
)
from Locations l, Answers b
where l.idlocation=b.idlocation and b.question_number='05'
In the table Answers I am saving sometimes a date string type of value for its field answer_text2 but on a different question number.
When I run the query I get the following error:
Conversion failed when converting the varchar value '27/12/2013' to data type int
I do have that value '27/12/2013' on the answer_text2 field but for a different question, so my filter gets ignored on the nested select statement after this: b.idlocation=c.idlocation, and it's adding up apparently more questions hence the error posted.
Update
According to Steve's suggested solution, I ended up implementing the filter to avoid char/varchar considerations into my SUM statement with a little variant:
Every possible not INT string value has a length greater than 2 ('00' to '99' for my question numbers) so I use this filter to determine when I am going to apply the cast.
'RESULT' =
case when (
select sum(
case when len(c.answer_text1) <= 2 then
cast(isnull(c.answer_text1,'0') as int)
else
0
end
) +
sum(
case when len(c.answer_text2) <= 2 then
cast(isnull(c.answer_text2,'0') as int)
else
0
end
)
from Answers c
where c.idlocation=b.idlocation and c.question_number='05'
) > 0
then
1
else
0
end
This is an unfortunate result of how the SQL Server query processor/optimizer works. In my opinion, the SQL standard prohibits the calculation of SELECT list expressions before the rows that will contribute to the result set have been identified, but the optimizer considers plans that violate this prohibition.
What you're observing is an error in the evaluation of a SELECT list item on a row that is not in the result set of your query. While this shouldn't happen, it does, and it's somewhat understandable, because to protect against it in every situation would exclude many efficient query plans from consideration. The vast majority of SELECT expressions will never raise an error, regardless of data.
What you can do is try to protect against this with an additional CASE expression. To protect against strings with the '/' character, for example:
... SUM(CASE WHEN c.answer_text1 IS NOT NULL and c.answer_text1 NOT LIKE '%/%' THEN CAST(c.answer_text1 as int) ELSE 0 END)...
If you're using SQL Server 2012, you have a better option: TRY_CONVERT:
...SUM(COALESCE(TRY_CONVERT(int,c.answer_text1),0)...
In your particular case, the overall database design is flawed, because numeric information should be stored in number-type columns. (This, of course, may not be your fault.) So redesign is an option, putting integer answers in integer-type columns and non-integer answer_text elsewhere. A compromise, if you can't redesign the tables, that I think will work, is to add a persisted computed column with value TRY_CONVERT(int,c.answer_text1) (or its best equivalent, based on what you know about the actual data in the table - perhaps the integer value of only columns containing no non-digit character and having length less than 9).
Your query appears correct enough, which means you have a Question 05 record with a datetime in either the answer_text1 or answer_text2 field.
Give this a shot to figure out which row has a date:
select *
from Answers
where question_number='05'
and (isdate(answer_text1) = 1 or isdate(answer_text2) = 1)
Furthermore, you could filter out any rows that have dates in them
where isdate(c.answer_text1) = 0
and isdate(c.answer_text2) = 0
and ...
Another option similar in nature to Steve's excellent answer is to filter your Answers table with a subquery like so:
select
l.idlocation,
'RESULT' = (
case when (
select
sum(cast(isnull(c.answer_text1,0) as int)) +
sum(cast(isnull(c.answer_text2,0) as int))
from (select answer_text1, answer_text2, idlocation from Answers where question_number ='05') c
where b.idlocation=c.idlocation
) > 0 then
1
else
0
end
)
from Locations l, Answers b
where l.idlocation=b.idlocation and b.question_number='05'
More generally, though, you could just have this query like this
select locations.idlocation, case when sum(case when is_numeric(answer_text1) then answer_text1 else 0 end) + sum(case when is_numeric(answer_text2) then answer_text2 else 0 end) > 0 then 1 else 0 end as RESULT from locations
inner join answers on answers.idlocation = locations.idlocation
where answers.question_number ='05'
group by locations.idlocation
Which would produce the same result.
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.
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
I need to calculate the net total of a column-- sounds simple. The problem is that some of the values should be negative, as are marked in a separate column. For example, the table below would yield a result of (4+3-5+2-2 = 2). I've tried doing this with subqueries in the select clause, but it seems unnecessarily complex and difficult to expand when I start adding in analysis for other parts of my table. Any help is much appreciated!
Sign Value
Pos 4
Pos 3
Neg 5
Pos 2
Neg 2
Using a CASE statement should work in most versions of sql:
SELECT SUM( CASE
WHEN t.Sign = 'Pos' THEN t.Value
ELSE t.Value * -1
END
) AS Total
FROM YourTable AS t
Try this:
SELECT SUM(IF(sign = 'Pos', Value, Value * (-1))) as total FROM table
I am adding rows from a single field in a table based on values from another field in the same table using oracle 11g as database and sql developer as user interface.
This works:
SELECT COUNTRY_ID, SUM(
CASE
WHEN ACCOUNT IN 'PTBI' THEN AMOUNT
WHEN ACCOUNT IN 'MLS_ENT' THEN AMOUNT
WHEN ACCOUNT IN 'VAL_ALLOW' THEN AMOUNT
WHEN ACCOUNT IN 'RSC_DEV' THEN AMOUNT * -1
END) AS TI
FROM SAMP_TAX_F4
GROUP BY COUNTRY_ID;
select a= sum(Value) where Sign like 'pos'
select b = sum(Value) where Signe like 'neg'
select total = a-b
this is abit sql-agnostic, since you didnt say which db you are using, but it should be easy to adapat it to any db out there.