SQL - count the number of occurrences in all columns

Question

I am trying to create some validation routines for an analytics system.

We have large tables with data. If a particular calculation all or most of a column might be zero. In practice values aren't usually exactly 0, so many occurrences of 0 indicates a potential issue. I want to write a single query that counts the number of 0's in each columnn. For instance, if my data was:

col1	col2	col3	col4	col5
1	0	23	2	9
2	0	54	3	-2
3	3	45	4	3
4	0	32	0	1
5	0	0	0	9

I would like to get a count of the number of occurrences of 0 in each column. The result for the table above would be: (0,4,1,2,0)

Is there a good way to do this in SQL for tables with an arbitrary number of columns?

Obviously I can't do:

select count(col1), count(col2), count(col3), count(col4), count(col5)
from table 
where col1 = 0 and col2 = 0 and col3 = 0 and col4 = 0 and col5=0

Answer 1

Use conditional aggregation here:

SELECT
    COUNT(CASE WHEN col1 = 0 THEN 1 END) AS cnt_col1,
    COUNT(CASE WHEN col2 = 0 THEN 1 END) AS cnt_col2,
    COUNT(CASE WHEN col3 = 0 THEN 1 END) AS cnt_col3,
    COUNT(CASE WHEN col4 = 0 THEN 1 END) AS cnt_col4,
    COUNT(CASE WHEN col5 = 0 THEN 1 END) AS cnt_col5
FROM yourTable;

Note that on databases which support summing boolean expressions, the above might be simplified to:

SELECT
    SUM(col1 = 0) AS cnt_col1,
    SUM(col2 = 0) AS cnt_col2,
    SUM(col3 = 0) AS cnt_col3,
    SUM(col4 = 0) AS cnt_col4,
    SUM(col5 = 0) AS cnt_col5
FROM yourTable;

Answer 2

I would suggest using WHERE condition and conditional aggregation to filter the row before aggregation as follows:

SELECT COUNT(CASE WHEN col1 = 0 THEN 1 END) AS col1_0_count,
       COUNT(CASE WHEN col2 = 0 THEN 1 END) AS col2_0_count,
       COUNT(CASE WHEN col3 = 0 THEN 1 END) AS col3_0_count,
       COUNT(CASE WHEN col4 = 0 THEN 1 END) AS col4_0_count,
       COUNT(CASE WHEN col5 = 0 THEN 1 END) AS col5_0_count
  FROM yourTable t
 WHERE 0 IN (col1, col2, col3, col4, col5);

Answer 3

SELECT SUM(case when col1 = 0 then 1 else 0 end) col1_0,
SUM(case when col2 = 0 then 1 else 0 end) col2_0,
SUM(case when col3 = 0 then 1 else 0 end) col3_0,
SUM(case when col4 = 0 then 1 else 0 end) col4_0
FROM yourTable;