When I need to get the number of row(data) inside a SQLite database, I run the following pseudo code.
cmd = "SELECT Count(*) FROM benchmark"
res = runcommand(cmd)
read res to get result.
But, I'm not sure if it's the best way to go. What would be the optimum way to get the number of data in a SQLite DB? I use python for accessing SQLite.
Your query is correct but I would add an alias to make it easier to refer to the result:
SELECT COUNT(*) AS cnt FROM benchmark
Regarding this line:
count size of res
You don't want to count the number of rows in the result set - there will always be only one row. Just read the result out from the column cnt of the first row.
Related
I have this code in SAS, I'm trying to write SQL equivalent. I have no experience in SAS.
data Fulls Fulls_Dupes;
set Fulls;
by name, coeff, week;
if rid = 0 and ^last.week then output Fulls_Dupes;
else output Fulls;
run;
I tried the following, but didn't produce the same output:
Select * from Fulls where rid = 0 groupby name,coeff,week
is my sql query correct ?
SQL does not have a concept of observation order. So there is no direct equivalent of the LAST. concept. If you have some variable that is monotonically increasing within the groups defined by distinct values of name, coeff, and week then you could select the observation that has the maximum value of that variable to find the observation that is the LAST.
So for example if you also had a variable named DAY that uniquely identified and ordered the observations in the same way as they exist in the FULLES dataset now then you could use the test DAY=MAX(DAY) to find the last observation. In PROC SQL you can use that test directly because SAS will automatically remerge the aggregate value back onto all of the detailed observations. In other SQL implementations you might need to add an extra query to get the max.
create table new_FULLES as
select * from FULLES
group by name, coeff, week
having day=max(day) or rid ne 0
;
SQL also does not have any concept of writing two datasets at once. But for this example since the two generated datasets are distinct and include all of the original observations you could generate the second from the first using EXCEPT.
So if you could build the new FULLS you could get FULLS_DUPES from the new FULLS and the old FULLS.
create table FULLS_DUPES as
select * from FULLES
except
select * from new_FULLES
;
I am trying to run a query that calculate with a countif function but I am having trouble with it. I have used the count and the iif functions in the builder but I think something weird is going on. I am trying to count the number of times a certain value occurs in a column so I do not want a specific value to equal to if that's possible?
Thanks!
To count the number of times a value appears you can use something like.
If you want to know how many times each value appears just omit the WHERE clause (without a sample of data I've used a table in the database I'm working on).
SELECT ProcessID,
COUNT(ProcessID)
FROM tbl_PrimaryData_Step1
WHERE ProcessID = 4
GROUP BY ProcessID
if you need just the value you can use:
SELECT COUNT(ProcessID)
FROM tbl_PrimaryData_Step1
WHERE ProcessID = 4
GROUP BY ProcessID
Another way is:
SELECT DCOUNT("ProcessID","tbl_PrimaryData_Step1","ProcessID = 4")
Edit:
In reply to your comment on your original post this SQL will give the result you're after:
SELECT Concatenate,
COUNT(Concatenate)
FROM MyTable
GROUP BY Concatenate
To display my results from PDO, I always use following PHP code for example:
$STH = $DBH->prepare("SELECT logo_id, guess_count, guessed, count(id) AS counter FROM guess WHERE user_id=:id");
$STH->bindParam(":id",$loginuser['id']);
$STH->execute();
while($row = $STH->fetch()){
print_r($row);
}
Now the issue is that I only get one result. I used to use $STH->rowCount() to check the amount of rows returned, but this method isn't really advised for SELECT statements because in some databases it doesn't react correctly. So I used the count(id) AS counter, but now I only get one result every time, even though the value of $row['counter'] is larger than one.
What is the correct way to count the amount of results in one query?
If you want to check the number of rows that are returned by a query, there are a couple of options.
You could do a ->fetchAll to get an array of all rows. (This isn't advisable for large result sets (i.e. a lot of rows returned by the query); you could add a LIMIT clause on your query to avoid returning more than a certain number of rows, if what you are checking is whether you get more than one row back, you would only need to retrieve two rows.) Checking the length of the array is trivial.
Another option is to run a another, separate query, to get the count separately, e.g.
SELECT COUNT(1) AS counter FROM guess WHERE user_id=:id
But, that approach requires another round trip to the database.
And the old standby SQL_CALC_ROUND_ROWS is another option, though that too can have problematic performance with large sets.
You could also just add a loop counter in your existing code:
$i = 0;
while($row = $STH->fetch()){
$i++
print_r($row);
}
print "fetched row count: ".$i;
If what you need is an exact count of the number of rows that satisfy a particular predicate PRIOR to running a query to return the rows, then the separate COUNT(1) query is likely the most suitable approach. Yes, it's extra code in your app; I recommend you preface the code with a comment that indicates the purpose of the code... to get an exact count of rows that satisfy a set of predicates, prior to running a query that will retrieve the rows.
If I had to process the rows anyway, and adding LIMIT 0,100 to the query was acceptable, I would go for the ->fetchAll(), get the count from the length of the array, and process the rows from the array.
You have to use GROUP BY. Your query should look like
SELECT logo_id, guess_count, guessed, COUNT(id) AS counter
FROM guess
WHERE user_id=:id
GROUP BY logo_id, guess_count, guessed
I am writing reports using Report Builder 3, and I need some help with an sql query to get unique values.
Using the following sample data:
I need to be able to get one single value for feeBudRec returned for each feeRef. The value of each feeBudRec is always the same for each individual feeRef (eg for every data row for feeRef LR01 will have a feeBudRec of 1177).
The reason why I need to get a single feeBudRec value for each feeRef is that I need to be able to total the feeBudRec value for each feeRef in a feePin (eg for feePin LEE, I need to total the feeBudRec values for LR01 and PS01, which should be 1177 + 1957 to get a total of 3134; but if I don't have unique values for feeBudRec, it will add the values for each row, which would bring back a total of 11756 for the 8 LEE rows).
My experience with writing SQL queries is very limited, but from searching the internet, it looks like I'll need to put in a subquery into my SQL query in order to get a single unique feeBudRec figure for each feeRef, and that a subquery that gets a minimum feeBudRec value for each feeRef should work for me.
Based on examples I've found, I think the following subquery should work:
SELECT a.feeRef, a.feeBudRec
FROM (
SELECT uvw_EarnerInfo.feeRef, Min(uvw_EarnerInfo.feeBudRec) as AvailableTime
FROM uvw_EarnerInfo
GROUP BY
uvw_EarnerInfo.feeRef
) as x INNER JOIN uvw_EarnerInfo as a ON a.feeRef = x.feeRef AND a.feeBudRec = x.AvailableTime;
The problem is that I have no idea how to insert that subquery into the query I'm using to produce the report (as follows):
SELECT
uvw_EarnerInfo.feeRef
,uvw_EarnerInfo.PersonName
,uvw_EarnerInfo.PersonSurname
,uvw_EarnerInfo.feePin
,uvw_RB_TimeLedger.TimeDate
,uvw_RB_TimeLedger.matRef
,uvw_RB_TimeLedger.TimeTypeCode
,uvw_RB_TimeLedger.TimeCharge
,uvw_RB_TimeLedger.TimeElapsed
,uvw_WoffTimeByTime.WoffMins
,uvw_WoffTimeByTime.WoffCharge
,uvw_EarnerInfo.feeBudRec
,uvw_EarnerInfo.personOccupation
FROM
uvw_RB_TimeLedger
LEFT OUTER JOIN uvw_WoffTimeByTime
ON uvw_RB_TimeLedger.TimeId = uvw_WoffTimeByTime.TimeId
RIGHT OUTER JOIN uvw_EarnerInfo
ON uvw_EarnerInfo.feeRef = uvw_RB_TimeLedger.feeRef
WHERE
uvw_RB_TimeLedger.TimeDate >= #TimeDate
AND uvw_RB_TimeLedger.TimeDate <= #TimeDate2
If that subquery will get the correct results, can anyone please help me with inserting it into my report query. Otherwise, can anyone let me know what I will need to do to get a unique feeBudRec value for each feeRef?
Depends on the exact schema, but assuming the uvw_EarnerInfo lists the Pin, Ref, and Rec without duplicates, try adding an extra column (after personOccupation) on the end of your query such as :
feeBudRecSum = (Select SUM(FeeBudRec) From uvw_EarnerInfo x
where x.feePin = uvw_EarnerInfo.feePin
Group By x.FeePin)
Note that you would not Sum these values in your report. This column should have the total you are looking for.
The key to Report Builder is to get your query correct from the offset and let the wizard then structure your report for you. It takes all the hard work out of structuring your report manually.
I haven't used Report Builder for a while now but in the query builder of the report displaying the graphical representation of your query you should be able to drag and drop columns in and out of the query set. Dragging a column upwards and out of the box (showing your columns) would have the effect of causing your report to break on this column.
If you restructure this way you will probably have to run the report generator again to regenerate the report and restructure it.
Once you are happy with the structure you can then begin to add the summary columns.
I guess this has been asked in the site before but I can't find it.
I've seen in some sites that there is a vague count over the results of a search. For example, here in stackoverflow, when you search a question, it says +5000 results (sometimes), in gmail, when you search by keywords, it says "hundreds" and in google it says aprox X results. Is this just a way to show the user an easy-to-understand-a-huge-number? or this is actually a fast way to count results that can be used in a database [I'm learning Oracle at the moment 10g version]? something like "hey, if you get more than 1k results, just stop and tell me there are more than 1k".
Thanks
PS. I'm new to databases.
Usually this is just a nice way to display a number.
I don't believe there is a way to do what you are asking for in SQL - count does not have an option for counting up until some number.
I also would not assume this is coming from SQL in either gmail, or stackoverflow.
Most search engines will return a total number of matches to a search, and then let you page through results.
As for making an exact number more human readable, here is an example from Rails:
http://api.rubyonrails.org/classes/ActionView/Helpers/NumberHelper.html#method-i-number_to_human
With Oracle, you can always resort to analytical functions in order to calculate the exact number of rows about to be returned. This is an example of such a query:
SELECT inner.*, MAX(ROWNUM) OVER(PARTITION BY 1) as TOTAL_ROWS
FROM (
[... your own, sorted search query ...]
) inner
This will give you the total number of rows for your specific subquery. When you want to apply paging as well, you can further wrap these SQL parts as such:
SELECT outer.* FROM (
SELECT * FROM (
SELECT inner.*,ROWNUM as RNUM, MAX(ROWNUM) OVER(PARTITION BY 1) as TOTAL_ROWS
FROM (
[... your own, sorted search query ...]
) inner
)
WHERE ROWNUM < :max_row
) outer
WHERE outer.RNUM > :min_row
Replace min_row and max_row by meaningful values. But beware that calculating the exact number of rows can be expensive when you're not filtering using UNIQUE SCAN or relatively narrow RANGE SCAN operations on indexes. Read more about this here: Speed of paged queries in Oracle
As others have said, you can always have an absolute upper limit, such as 5000 to your query using a ROWNUM <= 5000 filter and then just indicate that there are more than 5000+ results. Note that Oracle can be very good at optimising queries when you apply ROWNUM filtering. Find some info on that subject here:
http://www.dba-oracle.com/t_sql_tuning_rownum_equals_one.htm
Vague count is a buffer which will be displayed promptly. If user wants to see more results then he can request more.
It's a performance facility, after displaying the results the sites like google keep searching for more results.
I don't know how fast this will run, but you can try:
SELECT NULL FROM your_tables WHERE your_condition AND ROWNUM <= 1001
If count of rows in result will equals to 1001 then total count of records will > 1000.
this question gives some pretty good information
When you do an SQL query you can set a
LIMIT 0, 100
for example and you will only get the first hundred answers. so you can then print to your viewer that there are 100+ answers to their request.
For google I couldn't say if they really know there is more than 27'000'000'000 answer to a request but I believe they really do know. There are some standard request that have results stored and where the update is done in the background.