问题
I am trying to find the Chi-Square test from my following SQL Server Query on the sample data:
SELECT sessionnumber, sessioncount, timespent, expected, dev, dev*dev/expected as chi_square
FROM (SELECT clusters.sessionnumber, clusters.sessioncount, clusters.timespent,
(dim1.cnt * dim2.cnt * dim3.cnt)/(dimall.cnt*dimall.cnt) as expected,
clusters.cnt-(dim1.cnt * dim2.cnt * dim3.cnt)/(dimall.cnt*dimall.cnt) as dev
FROM clusters JOIN
(SELECT sessionnumber, SUM(cnt) as cnt FROM clusters
GROUP BY sessionnumber) dim1 ON clusters.sessionnumber = dim1.sessionnumber JOIN
(SELECT sessioncount, SUM(cnt) as cnt FROM clusters
GROUP BY sessioncount) dim2 ON clusters.sessioncount = dim2.sessioncount JOIN
(SELECT timespent, SUM(cnt) as cnt FROM clusters
GROUP BY timespent) dim3 ON clusters.timespent = dim3.timespent CROSS JOIN
(SELECT SUM(cnt) as cnt FROM clusters) dimall) a
My table has this sort of sample data:
sessionnumber sessioncount timespent cnt
1 17 28 NULL
2 22 8 NULL
3 1 1 NULL
4 1 1 NULL
5 8 111 NULL
6 8 65 NULL
7 11 5 NULL
8 1 1 NULL
9 62 64 NULL
10 6 42 NULL
The problem is that this query works fine but it gives wrong output or you can say no output at all. The output it gives my is like:
sessionnumber sessioncount timespent expected dev chi_square
1 17 28 NULL NULL NUL
2 22 8 NULL NULL NULL
3 1 1 NULL NULL NULL
4 1 1 NULL NULL NULL
5 8 111 NULL NULL NULL
6 8 65 NULL NULL NULL
7 11 5 NULL NULL NULL
8 1 1 NULL NULL NULL
9 62 64 NULL NULL NULL
10 6 42 NULL NULL NULL
How can I get rid of this problem because I tried my best at all! Thanks in advance telling me what I' doing wrong!
回答1:
In your sample data, cnt is NULL, so the results are also NULL. You can replace these NULL values with a default value (1 for example, I don't know what is the context) using ISNULL, like
SELECT sessionnumber, SUM(ISNULL(cnt, 1)) as cnt FROM clusters GROUP BY sessionnumber
来源：https://stackoverflow.com/questions/18014961/sql-server-query-to-find-chi-square-values-not-working