I am trying to do aggregations in case statement. I found 2 ways to do it. Can anyone say what the difference between the 2 is?
(CASE WHEN Event = 5 THEN count(*) ELSE 0 END ) Follow_Count
GROUP BY Event;
SUM(CASE Event WHEN 5 THEN 1 ELSE 0 END) AS Follow_Count
Your case 1 will produce a row for each event in the table (from your group by). Your case 2 will just return 1 row.
Is there a reason that you wouldn't just write:
select count(*)
from my_table
where event = 5;
Better would be:
count(CASE Event WHEN 5 THEN 1 END) AS Follow_Count
Because
1) for count used own standart counter,
2) "else" not need (count don't count nulls)
Regards,
Sayan M.
There is no significant difference. You can decide for you which is better by comparing their execution plans.
Related
I have a line of SQL which produces a count of purchases variable
count(distinct case when t.transaction_sub_type =1 then t.transaction_date end) as COUNTPUR,
I need to modify this so I can produce a 0/1 flag variable, which flags if a customer is a repeat purchaser. So, when a customer's purchases are greater than 1 then flag as 1 else flag as 0.
case when COUNTPUR>1 then 1 else 0 end as FLAG_REPEATPURCHASER
I need to combine these two case statements into one. I have been experimenting with different versions of the syntax, but I can't seem to nail it down. Below is one of the experiments which do not work.
max(case when (count(distinct case when t.transaction_sub_type =1 then t.transaction_date end))>1 then 1 else 0 end) as FLAG_REPEATPURCHASER,
Thanks in advance for assitance
You can use a case expression with conditional aggregation:
(case when count(distinct case when t.transaction_sub_type = 1 then t.transaction_date end) > 1
then 1 else 0
end) as FLAG_REPEATPURCHASER
I have a column MessageId and have to take the count of distinct MessageId and if the result is 1, then have to display count as 0 else the count value itself. If the data set is more, using distinct twice is going to be a bit more time consuming.
...
CASE
WHEN count(DISTINCT MessageId) = 1
THEN 0
ELSE count(DISTINCT MessageId)
END as Count
...
Is there anyway to use COUNT(DISTINCT) only once using a single query itself? And also don't want to use multiple queries like assigning it to a variable and then using it.
Here is one method:
COALESCE(NULLIF(COUNT(DISTINCT MessageId), 1), 0)
it seems you need below
case when sum( case when MessageId= 1 then 1 else 0 end) =1
then 0 else
count(DISTINCT MessageId) end as cnt
SELECT
qt.name,
CASE
WHEN qr.isfinished = 0 THEN COUNT(qr.resultid)
END AS 'Attempted',
CASE
WHEN qr.isfinished = 1 THEN COUNT(qr.resultid)
END AS 'Completed'
Need it to show attempted and completed values on the same row
Name attempted Completed
--------------------------------
Algebra I 114 NULL
Algebra II 47 NULL
ASVAB 55 NULL
Algebra I NULL 69
Algebra II NULL 55
ASVAB NULL 84
Thank you for the help!
If isfinished is bit, you can't aggregate on it.
And the CASE goes inside the COUNT
SELECT qt.name,
count(Case when qr.isfinished = 0 THEN 1 END) as 'Attempted',
count(Case when qr.isfinished = 1 THEN 1 END) as 'Completed'
FROM
...
GROUP BY
qt.name
There are multiple ways you could do this, for example you could do this with joins, or you can use group by -- like so:
SELECT
qt.name,
SUM(CASE qr.isfinsihed WHEN 1 THEN 1 ELSE 0) AS 'Attempted',
SUM(CASE qr.isfinished WHEN 0 THEN 1 ELSE 0) AS 'Completed'
FROM -- what ever your from clause is, it goes here --
GROUP BY
qt.name
In order to have them on the same row, you will need to group by what they have in common. From what you have given in the question, I am assuming that is the qt.name.
Next, you can use the SUM aggregate to get each field count. All of the records that meet the criteria for each item count towards the sum, the others don't. You can also use count with 1's and Null's, I prefer using Sum because it can allow for weighted totals if I need them.
SELECT round(COUNT(dmd_1wk),2) AS NBR_ITEMS_1WK
FROM table;
Field dmd_1wk has so many zeros in it. How do I Count the non zero values?
It sounds like you just need to add a WHERE clause:
SELECT
round(COUNT(dmd_1wk),2) AS NBR_ITEMS_1WK
FROM table
WHERE dmd_1wk <> 0;
If you want the count of both non-zero and zero values, then you can use something like:
SELECT
round(COUNT(case when dmd_1wk <> 0 then dmd_1wk end),2) AS NBR_ITEMS_1WK_NonZero,
round(COUNT(case when dmd_1wk = 0 then dmd_1wk end),2) AS NBR_ITEMS_1WK_Zero
FROM table;
Method 1: Case Statement. This may be useful if you need to continue to process all rows (which a where clause would prevent).
SELECT count(case when dmd_1wk = 0 then 0 else 1 end) as NonZeroCount FROM MyTable
Method 2: Where Clause.
SELECT
count(1) as NonZeroCount
FROM
MyTable
WHERE
dmd_1wk <> 0
I'd like to offer another solution using NULLIF since COUNT won't count NULL values:
SELECT round(COUNT(NULLIF(dmd_1wk,0)),2) AS NBR_ITEMS_1WK
FROM table;
And here is the Fiddle.
Good luck.
Methinks bluefeets answer is probably what you are really looking for, as it sounds like you just want to count non-zeros; but this will get you a count of zero and non-zero items if that's not the case:
SELECT
ROUND(SUM(CASE NVL(dmd_1wk, 0) = 0 THEN 1 ELSE 0 END), 2) AS "Zeros",
ROUND(SUM(CASE NVL(dmd_1wk, 0) != 0 THEN 1 ELSE 0 END), 2) AS "NonZeros"
FROM table
Although there is no point in rounding a whole number, I've included your original ROUNDs as I'm guessing you're using it for formatting, but you might want to use:
TO_CHAR(SUM(...), '999.00')
as that's the intended function for formatting numbers.
You can filter them.
SELECT round(COUNT(dmd_1wk),2) AS NBR_ITEMS_1WK
FROM table
WHERE dmd_1wk <> 0;
I have a table and I need calculate two aggregate functions with different conditions in one statement. How can I do this?
Pseudocode below:
SELECT count(CoumntA) *< 0*, count(CoumntA) * > 0*
FROM dbo.TableA
This is the same idea as tombom's answer, but with SQL Server syntax:
SELECT
SUM(CASE WHEN CoumntA < 0 THEN 1 ELSE 0 END) AS LessThanZero,
SUM(CASE WHEN CoumntA > 0 THEN 1 ELSE 0 END) AS GreaterThanZero
FROM TableA
As #tombom demonstrated, this can be done as a single query. But it doesn't mean that it should be.
SELECT
SUM(CASE WHEN CoumntA < 0 THEN 1 ELSE 0 END) AS less_than_zero,
SUM(CASE WHEN CoumntA > 0 THEN 1 ELSE 0 END) AS greater_than_zero
FROM
TableA
The time when this is not so good is...
- There is an index on CoumntA
- Most values (50% or more feels about right) are exactly zero
In that case, two queries will be faster. This is because each query can use the index to quickly home in on the section to be counted. In the end only counting the relevant records.
The example I gave, however, scans the whole table every time. Only once, but always the whole table. This is worth it when you're counting most of the records. In your case it looks liek you're counting most or all of them, and so this is probably a good way of doing it.
It is possible to do this in one select statement.
The way I've done it before is like this:
SELECT SUM(CASE WHEN ColumnA < 0 THEN 1 END) AS LessThanZero,
SUM(CASE WHEN ColumnA > 0 THEN 1 END) AS GreaterThanZero
FROM dbo.TableA
This is the correct MS SQL syntax and I believe this is a very efficient way of doing it.
Don't forget you are not covering the case when ColumnA = 0!
select '< 0' as filter, COUNT(0) as cnt from TableA where [condition 1]
union
select '> 0' as filter, COUNT(0) as cnt from TableA where [condition 2]
Be sure that condition 1 and condition 2 create a partition on the original set of records, otherwise same records could be counted in both groups.
For SQL Server, one way would be;
SELECT COUNT(CASE WHEN CoumntA<0 THEN 1 ELSE NULL END),
COUNT(CASE WHEN CoumntA>0 THEN 1 ELSE NULL END)
FROM dbo.TableA
Demo here.
SELECT
SUM(IF(CoumntA < 0, 1, 0)) AS lowerThanZero,
SUM(IF(CoumntA > 0, 1, 0)) AS greaterThanZero
FROM
TableA
Is it clear what's happening? Ask, if you have any more questions.
A shorter form would be
SELECT
SUM(CoumntA < 0) AS lowerThanZero,
SUM(CoumntA > 0) AS greaterThanZero
FROM
TableA
This is possible, since in MySQL a true condition is equal 1, a false condition is equal 0
EDIT: okay, okay, sorry, don't know why I thought it's about MySQL here.
See the other answers about correct syntax.