Solved

query syntax

Posted on 2014-09-15
6
103 Views
Last Modified: 2014-09-17
Hello,

Not really sure how Counts, sum and procents work.

I have a table with a few rows like this

id   x1       x2
1    null     0
2    1         1
3    1         null
4    0         null

Open in new window


where i am looking for the procentage of rows that have a 1 in the x1 and x2 columns.  Null rows should not be included.

so x1 procent should be 66% and x2 should be 50%

I am having trouble because i am not sure if there is a standard function that will do this, or what the most efficient way would be if one does not exist.

Its important that it is efficient because we are talking about a lot of rows and many more columns.

/thanks
0
Comment
Question by:soozh
  • 3
  • 3
6 Comments
 
LVL 48

Expert Comment

by:PortletPaul
ID: 40324427
SELECT
      COUNT(CASE WHEN x1 = 1 THEN 1 END)                   AS x1_1
    , COUNT(x1)                                            AS x1
    , CASE WHEN COUNT(x1) > 0 THEN 
           COUNT(CASE WHEN x1 = 1 THEN 1 END) * 100.0 / COUNT(x1)
           ELSE 0 
      END                                                  AS x1_pct
    , COUNT(CASE WHEN x2 = 1 THEN 1 END)                   AS x2_1
    , COUNT(x2)                                            AS x2
    , CASE WHEN COUNT(x2) > 0 THEN 
           COUNT(CASE WHEN x2 = 1 THEN 1 END) * 100.0 / COUNT(x2)
           ELSE 0
      END                                                 AS x2_pct
FROM table1
;

Open in new window

The aggregate function COUNT()  will only count non-null values (in other words it ignores nulls)
So the result of the query above is:
| X1_1 | X1 |          X1_PCT | X2_1 | X2 | X2_PCT |
|------|----|-----------------|------|----|--------|
|    2 |  3 | 66.666666666666 |    1 |  2 |     50 |

Open in new window

But do remember that divide by zero isn't allowed so if COUNT(X1) is zero you cannot attempt the percentage calculation

see: http://sqlfiddle.com/#!3/439ed/1
0
 
LVL 47

Expert Comment

by:Vitor Montalvão
ID: 40324790
soozh, check if this works and isn't slow:
select (count(x1)*1.0 / count(1))*100 as PercentX1, (count(x2)*1.0 / count(1))*100 as PercentX2
from YourTableNameHere

Open in new window

0
 
LVL 48

Assisted Solution

by:PortletPaul
PortletPaul earned 300 total points
ID: 40324801
In case it isn't obvious, I included more columns than you requested so you could follow the calculations. The unwanted columns can be removed. e.g.
SELECT
      CASE WHEN COUNT(x1) > 0 THEN 
           COUNT(CASE WHEN x1 = 1 THEN 1 END) * 100.0 / COUNT(x1)
           ELSE 0 
      END                                                  AS x1_pct
    , CASE WHEN COUNT(x2) > 0 THEN 
           COUNT(CASE WHEN x2 = 1 THEN 1 END) * 100.0 / COUNT(x2)
           ELSE 0
      END                                                 AS x2_pct
FROM table1
;

Open in new window

0
Enterprise Mobility and BYOD For Dummies

Like “For Dummies” books, you can read this in whatever order you choose and learn about mobility and BYOD; and how to put a competitive mobile infrastructure in place. Developed for SMBs and large enterprises alike, you will find helpful use cases, planning, and implementation.

 
LVL 47

Expert Comment

by:Vitor Montalvão
ID: 40324810
PortletPaul, why are you not counting the zeros?
The idea is not to return the percentage of rows that doesn't have NULL value for each column? Or I misunderstood?
0
 
LVL 48

Expert Comment

by:PortletPaul
ID: 40324864
because that is required, and non-null values of x1 or x2 are to be counted.

>>"so x1 procent should be 66% and x2 should be 50%"


X1 has 3 non-null values, 2 of those = 1 hence: 2/3 = 66%
x2 has 2 non-null values, 1 of those = 1 hence: 1/2 = 50%

you are counting all records through count(1) [ it's the same as count(*)] which is 4
you are then counting x1 or x2

so you get:
3 values of x1 / 4 rows = 75%
2 values of x2 / 4 rows = 50%

try it here: http://sqlfiddle.com/#!3/439ed/2
0
 
LVL 47

Accepted Solution

by:
Vitor Montalvão earned 200 total points
ID: 40324975
Ok. I can see that I misunderstood the question.
The only way to simplify your query is if the values are only 0 and 1, so you can SUM them instead of counting:
select (sum(x1)*1.0 / count(1))*100 as PercentX1, (sum(x2)*1.0 / count(1))*100 as PercentX2
from YourTableNameHere

Open in new window

0

Featured Post

3 Use Cases for Connected Systems

Our Dev teams are like yours. They’re continually cranking out code for new features/bugs fixes, testing, deploying, testing some more, responding to production monitoring events and more. It’s complex. So, we thought you’d like to see what’s working for us.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

'Between' is such a common word we rarely think about it but in SQL it has a very specific definition we should be aware of. While most database vendors will have their own unique phrases to describe it (see references at end) the concept in common …
In this article I will describe the Copy Database Wizard method as one possible migration process and I will add the extra tasks needed for an upgrade when and where is applied so it will cover all.
Established in 1997, Technology Architects has become one of the most reputable technology solutions companies in the country. TA have been providing businesses with cost effective state-of-the-art solutions and unparalleled service that is designed…
Email security requires an ever evolving service that stays up to date with counter-evolving threats. The Email Laundry perform Research and Development to ensure their email security service evolves faster than cyber criminals. We apply our Threat…

810 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question