I am writing a query like this
select case #flag
when 'Y' then (select * from some table which is having multiple column)
when 'N' then (select * from some table which is having multiple column)
end
as Result
,#flag:='Y'
but it is showing Operand should contain 1 column(s).
I Know that case can only return one column but just want to know if any way is available for this.
You need to select a column in the subqueries:
select (case #flag
when 'Y' then (select col from some table which is having multiple column)
----------------------------------^
when 'N' then (select col from some table which is having multiple column)
end) as Result,
#flag:='Y'
Related
I have a query structured like below, it checks if any of the entry in a given column is not null, if it finds a match (a value that is not null) it immediately returns Y, if all values are null it returns N. It works with a column called first_name but I need to make it work for other columns as well i.e last_name, middle_name, preferably all in a single query to save execution time. Y or N must be returned for each of the columns specified.
SELECT CASE
WHEN EXISTS(SELECT *
FROM (patient AS p JOIN patient_score AS s ON p.patient_id=s.patient_id)
WHERE first_name IS NOT NULL)
THEN 'Y'
ELSE 'N'
END AS your_result
I have another query which is an alternative and does the same job (1/0 instead of Y/N). But I don't know how to make it work with multiple columns either. A procedure that could work by supplying multiple column names would work as well.
SELECT COUNT(*) AS fn FROM
(SELECT 1
FROM (patient AS p JOIN patient_score AS s ON p.patient_id=s.patient_id)
WHERE first_name IS NOT NULL
LIMIT 1) AS T;
I think it is the query that you want, you have to add a SELECT element (CASE WHEN SUM(CASE WHEN column_name IS NULL THEN 0 ELSE 1 END) > 0 THEN 'Y' ELSE 'N' END AS column_name) for each column you want to check.
SELECT
CASE WHEN SUM(CASE WHEN first_name IS NULL THEN 0 ELSE 1 END) > 0 THEN 'Y' ELSE 'N' END AS first_name
FROM patient AS p
INNER JOIN patient_score AS s ON p.patient_id = s.patient_id
I think there is no question like this.
I need to group rows by n records and get some values of this group.
I think is better to explain with a graphic example:
Is possible to do a query like this? if not my solution will be make an script to create another table with this but I don´t like duplicate data at all.
Thanks!!!
set #counter=-1;
select xgroup,max(x) as mx, max(y) as my, avg(value3) as v3,
from
(
select (#counter := #counter +1) as counter,
#counter div 5 as xgroup,
currency, datetime, value1, value2,
case mod(#counter,5) when 0 then value1 else 00 end as x,
case mod(#counter,5) when 4 then value2 else 00 end as y,
mod(#counter,5) as xxx
FROM findata
) name1
group by xgroup;
#jms has the right approach, but you have to be very careful when using variables:
You should not assign a variable in one expression and then reference it in another in the same select.
To work in the most recent versions of MySQL, I would suggest ordering the data in a subquery.
In addition, there are some other values that you need:
select min(col1), min(col2),
max(case when mod(rn, 5) = 0 then col3 end),
max(col4), min(col5),
max(case when mod(rn, 5) or rn = #rn then col6 end),
max(case when mod(rn, 5) or rn = #rn then col7 end)
from (select (#rn := #rn + 1) as rn, t.*
from (select t.*
from t
order by col1, col2
) t cross join
(select #rn := -1) params
) t
group by (#rn div 5);
Note the logic is a bit arcane for the last values -- this is to take into account the final group that might not have exactly 5 rows.
You need a column that looks like(assuming you want to group every 5 rows)
dummy_table
1
1
1
1
1
2
2
2
2
2
...
You can do this by using generate_series() if you are using postgre sql by using
select t1 from (select generate_series(1,x)) t1, (select generate_series(1,5)) t2;
where you can replace x by (total rows/5) i.e. for 100 rows, x = 20. If you are using any other SQL platform, you can just work on creating this dummy table accordingly.
Once you get this dummy_table, join it with your table on row_number of your table with t1 column of dummy_table(not row_number of dummy_table). Syntax for accessing row number should be straightforward.
After the join, group by this t1 column and do the required aggregation. To do this in a single query, you can do the above in an inner query and do aggregation outside it. Hope this makes sense.
Ok, thanks you all guys for your answers, thanks to it I found the simple solution.
I simply add an autoincrement column, and then I can group results by integer division by 5.
And with this query:
SELECT id,
symbol,
datetime,
open,
MAX(high),
MIN(low),
SUBSTRING_INDEX( GROUP_CONCAT(CAST(close AS CHAR) ORDER BY datetime DESC), ',', 1 ) AS close
FROM `table`
GROUP BY (id-1) DIV 5
And the resulting is:
Thanks!
A solution is to introduce some field for grouping rows for aggregative operations.
It can be reached by introducing a user-variable and assigning values that will allow to group rows as required. For example, it can be a row counter divided by grouping chuck size and rounded to nearest upper ceil number:
SET #counter=0;
SELECT CEIL((#counter:=#counter+1)/5) AS chunk, MAX(high), MIN(low) FROM `table` GROUP BY chunk;
Suppose that my database looks something like the following:
First Entry | Second Entry | Third Entry
0 0 0
0 1 2
2 1 0
2 0 1
3 0 0
I am trying to return the subset of this table where an element in the FirstEntry column repeats at least once. So in this case it would return all but the final row. How can I go about this? I've tried using things such as count() but have only managed to achieve grouping instead of returning the actual rows I am curious in (in particular, I care aboout Second and Third entry but only when First entry has repeated at least once).
Using IN()
select * from your_table
where FirstEntry in
(
select FirstEntry
from your_table
group by FirstEntry
having count(*) > 1
)
or using a JOIN
select t1.*
from your_table t1
join
(
select FirstEntry
from your_table
group by FirstEntry
having count(*) > 1
) t2 on t1.FirstEntry = t2.FirstEntry
Try this:
select *
from my_table
where First_Entry IN(SELECT First_Entry From my_table
group by First_entry having count(*) > 1)
I'm trying to include select statement in the then of case statement but the output is not as expected. I know there is different method to do this but can it be done the way i'm trying to do.
Using the following example data:
create table example(name varchar(10));
insert into example values
('abc'),('bcd'),('xyz');
I have tried this query (here is the fiddle):
select
case when ((select * from example where name='abc')>=1)
then (select * from example where name='abc')
else (select count(*) from example)
end
from example
But it outputs
3
3
3
Expected output if name='abc' exist
name
abc
if not the count(*)
Thanks in advance
Your subquery in the example is (select * from example where name='abc') which is a result set, not a scalar value. Currently it "works" because it is comparing the only column in the table to the value 1 but if you had more than one column in the table it would error out. Perhaps you intended (select count(*) from example where name='abc')?
Similarly, the THEN clause in a case can only be used to provide a single column value. In order to do this, perhaps you meant the following:
select
case when exists (select * from example where name='abc')
then (select name from example where name='abc')
else (select count(*) from example)
end
from example
But even here you will get three rows and there is no correlation between the rows in example and the result set, so I am not really sure what you're trying to do. I imagine there is a higher purpose though so I will leave it at that.
This should do the trick
select distinct
case when ((select count(name) from example where name='abc')>=1)
then (select * from example where name='abc')
else (select count(*) from example)
end
from example
Let me know if it works.
Point 1:
For the query, you are trying, the from example in the last will cause to loop through all the records and fetch all the records. To restrict that, you have to remove that.
Point 2:
You can't combine multi row select * in a true condition with a single row count(*) in a false condition. You should limit to select a single row.
Example:
select
case when ( select count(*) from example where name='abc' ) >= 1
then ( select * from example where name='abc' limit 1 )
else ( select count(*) from example )
end as name
No need to bother with the complex queries.
SELECT COUNT(*) AS ct
FROM example
GROUP BY name = 'abc'
ORDER BY name = 'abc' DESC
LIMIT 1;
If you really want to use CASE just for the sake of using it:
SELECT
CASE name
WHEN 'abc' THEN 'abc'
ELSE 'others'
END AS name, COUNT(*) AS ct
FROM example
GROUP BY name = 'abc'
ORDER BY name = 'abc' DESC
LIMIT 1;
Try below query, which will work even you enter a second duplicate row as value 'abc'. Mostly above suggested queries will not work as you enter this duplicate row while as per your query condition (>=1), there can be multiple rows for name as 'abc'.
SELECT
CASE WHEN b.cnt>=1
THEN a.name
ELSE (SELECT COUNT(*) FROM EXAMPLE)
END
FROM (SELECT DISTINCT NAME FROM EXAMPLE WHERE NAME='abc') a
JOIN (SELECT NAME,COUNT(*) AS cnt FROM EXAMPLE WHERE NAME='abc') b
ON a.name=b.name
Desired result:
Return results ONLY for the first true encountered SELECT expression.
Explanation:
So, I have three different SELECT expresions:
SELECT * FROM table WHERE column1 = 'sometext' AND column2='1'
SELECT * FROM table WHERE column1 = 'someothertext' AND column2='2'
SELECT * FROM table WHERE column1 = 'somethirdtext' AND column2='3'
I want to have the results from 1. If 1. is returning NULL, I would like result from select number 2. If Select number 2. is returning NULL, I would like to use select number 3. and so on.
Please note that I am expecting more than one row to be returned for each condition that is true - and I only want the result from either SELECT 1) 2) or 3) (in that order)
It is important to only return results from the one single SELECT expression, so even if 2. and 3. would return something, I would only like results from 1.
The code I have right now is following that expected logic BUT when a I have more than one rows being returned by some of the below SELECTS, it gives me error:
1242 - Subquery returns more than 1 row
The code right now:
SELECT IFNULL( (SELECT * FROM table WHERE column = 'sometext'), IFNULL( (SELECT * FROM table WHERE column = 'someothertext'), IFNULL( (SELECT * FROM table WHERE column = 'somethirdtext'), 0 ) ) )
You're looking for COALESCE function.
SELECT COALESCE(
(SELECT col FROM t WHERE `column` = 'sometext'),
(SELECT col FROM t WHERE `column` = 'someothertext'),
(SELECT col FROM t WHERE `column` = 'somethirdtext')
);
-please, note that subquery should not return more than 1 row/column.
I would approach this slightly differently, since you can only return one row per condition anyway, I would use the following to limit the number of selects done:
SELECT *
FROM table
WHERE column IN ('sometext', 'someothertext', 'somethirdtext')
ORDER BY CASE column
WHEN 'sometext' THEN 1
WHEN 'someothertext' THEN 2
WHEN 'somethirdtext' THEN 3
END
LIMIT 1;
As pointed out in the comments, you can use FIELD for the sort too:
SELECT *
FROM table
WHERE column IN ('sometext', 'someothertext', 'somethirdtext')
ORDER BY FIELD(column, 'sometext', 'someothertext', 'somethirdtext')
LIMIT 1;
I think you can get multiple rows per condition using the following:
SELECT T.*
FROM Table T
INNER JOIN
( SELECT Column
FROM Table
WHERE column IN ('sometext', 'someothertext', 'somethirdtext')
ORDER BY FIELD(column, 'sometext', 'someothertext', 'somethirdtext')
LIMIT 1
) MinT
ON MinT.Column = T.Column;
Basically the subquery MinT does the same as before, ordering by whichever condition matches. Then gets the value for the column of the first match and limits the whole table to this value.
Example on SQL Fiddle
SELECT t.*
FROM
( SELECT o.column1, o.column2
FROM
( SELECT 1 AS ord, 'sometext' AS column1, '1' AS column2 UNION ALL
SELECT 2, 'someothertext', '2' UNION ALL
SELECT 3, 'somethirdtext', '3'
) AS o
WHERE EXISTS
( SELECT 1
FROM table AS td
WHERE td.column1 = o.column1
AND td.column2 = o.column2
)
ORDER BY o.ord
LIMIT 1
) AS d
JOIN
table AS t
ON t.column1 = d.column1
AND t.column2 = d.column2 ;
MySQL isn't my daily db so I might be off on this, but can't you just use LIMIT 1 on your subqueries?