Creating statistical data from a table - c++

Question

I have a table with 20 columns of measurements. I would like 'convert' the table into a table with 20 rows with columns of Avg, Min, Max, StdDev, Count types of information. There is another question like this but it was for the 'R' language. Other question here.
I could do the following for each column (processing the results with C++):
Select Count(Case When [avgZ_l1] <= 0.15 and avgZ_l1 > 0 then 1 end) as countValue1,
Count(case when [avgZ_l1] <= 0.16 and avgZ_l1 > 0.15 then 1 end) as countValue2,
Count(case when [avgZ_l1] <= 0.18 and avgZ_l1 > 0.16 then 1 end) as countValue3,
Count(case when [avgZ_l1] <= 0.28 and avgZ_l1 > 0.18 then 1 end) as countValue4,
Avg(avgwall_l1) as avg1, Min(avgwall_l1) as min1, Max(avgZ_l1) as max1,
STDEV(avgZ_l1) as stddev1, count(*) as totalCount from myProject.dbo.table1
But I do not want to process the 50,000 records 20 times (once for each column). I thought there would be away to 'pivot' the table onto its side and process the data at the same time. I have seen examples of the 'Pivot' but they all seem to pivot on a integer type field, Month number or Device Id. Once the table is converted I could then fetch each row with C++. Maybe this is really just 'Insert into ... select ... from' statements.
Would the fastest (execution time) approach be to simply create a really long select statement that returns all the information I want for all the columns?
We might end up with 500,000 rows. I am using C++ and SQL 2014.
Any thoughts or comments are welcome. I just don't want have my naive code to be used as a shining example of how NOT to do something... ;)...

Answer 1

If your table looks the same as the code that you sent in r then the following query should work for you. It selects the data that you requested and pivots it at the same time.
create table #temp(ID int identity(1,1),columnName nvarchar(50));
insert into #temp
SELECT COLUMN_NAME as columnName
FROM myProject.INFORMATION_SCHEMA.COLUMNS -- change myProject to the name of your database. Unless myProject is your database
WHERE TABLE_NAME = N'table1'; --change table1 to your table that your looking at. Unless table1 is your table
declare #TableName nvarchar(50) = 'table1'; --change table1 to your table again
declare #loop int = 1;
declare #query nvarchar(max) = '';
declare #columnName nvarchar(50);
declare #endQuery nvarchar(max)='';
while (#loop <= (select count(*) from #temp))
begin
set #columnName = (select columnName from #temp where ID = #loop);
set #query = 'select t.columnName, avg(['+#columnName+']) as Avg ,min(['+#columnName+']) as min ,max(['+#columnName+'])as max ,stdev(['+#columnName+']) as STDEV,count(*) as totalCount from '+#tablename+' join #temp t on t.columnName = '''+#columnName+''' group by t.columnName';
set #loop += 1;
set #endQuery += 'union all('+ #query + ')';
end;
set #endQuery = stuff(#endQuery,1,9,'')
Execute(#endQuery);
drop table #temp;
It creates a #temp table which stores the values of your column headings next to an ID. It then uses the ID when looping though the number of columns that you have. It then generates a query which selects what you want and then unions it together. This query will work on any number of columns meaning that if you add or remove more columns it should give the correct result.
With this input:
age height_seca1 height_chad1 height_DL weight_alog1
1 19 1800 1797 180 70
2 19 1682 1670 167 69
3 21 1765 1765 178 80
4 21 1829 1833 181 74
5 21 1706 1705 170 103
6 18 1607 1606 160 76
7 19 1578 1576 156 50
8 19 1577 1575 156 61
9 21 1666 1665 166 52
10 17 1710 1716 172 65
11 28 1616 1619 161 66
12 22 1648 1644 165 58
13 19 1569 1570 155 55
14 19 1779 1777 177 55
15 18 1773 1772 179 70
16 18 1816 1809 181 81
17 19 1766 1765 178 77
18 19 1745 1741 174 76
19 18 1716 1714 170 71
20 21 1785 1783 179 64
21 19 1850 1854 185 71
22 31 1875 1880 188 95
23 26 1877 1877 186 106
24 19 1836 1837 185 100
25 18 1825 1823 182 85
26 19 1755 1754 174 79
27 26 1658 1658 165 69
28 20 1816 1818 183 84
29 18 1755 1755 175 67
It will produce this output:
avg min max stdev totalcount
age 20 17 31 3.3 29
height_seca1 1737 1569 1877 91.9 29
height_chad1 1736 1570 1880 92.7 29
height_DL 173 155 188 9.7 29
weight_alog1 73 50 106 14.5 29
Hope this helps and works for you. :)