GROUP BY or COUNT Like Field Values - UNPIVOT?

Question

I have a table with test fields, Example

id         | test1    | test2    | test3    | test4    | test5
+----------+----------+----------+----------+----------+-         


        

Answer 1

I may have come up with a solution:

SELECT id
      ,l - length(replace(t, 'P', '')) AS nr_p
      ,l - length(replace(t, 'F', '')) AS nr_f
      ,l - length(replace(t, 'I', '')) AS nr_i
FROM   (SELECT id, test::text AS t, length(test::text) AS l  FROM test) t

The trick works like this:

• Transform the rowtype into its text representation.
• Measure character-length.
• Replace the character you want to count and measure the change in length.
• Compute the length of the original row in the subselect for repeated use.

This requires that P, F, I are present nowhere else in the row. Use a sub-select to exclude any other columns that might interfere.

Tested in 8.4 - 9.1. Nobody uses PostgreSQL 7.4 anymore nowadays, you'll have to test yourself. I only use basic functions, but I am not sure if casting the rowtype to text is feasible in 7.4. If that doesn't work, you'll have to concatenate all test-columns once by hand:

SELECT id
      ,length(t) - length(replace(t, 'P', '')) AS nr_p
      ,length(t) - length(replace(t, 'F', '')) AS nr_f
      ,length(t) - length(replace(t, 'I', '')) AS nr_i
FROM   (SELECT id, test1||test2||test3||test4 AS t FROM test) t

This requires all columns to be NOT NULL.