Count non-empty rows with unknown column names - sql-server

Question

Given a table that has unknown column names, how can I list all column names and the amount of rows that have a non-empty (NULL or empty string) value in that column?
Small example:
Col1 | Col2 | Col3 | dkasldk | dD? d3# !(
1 | | 2 | |
| 2 | d | ddd939 |
f | f | 84 | |
Should yield:
Column Name | Values
Col1 | 2
Col2 | 2
Col3 | 3
dkasldk | 1
dD? d3# !( | 0
I already tried around with using INFORMATION_SCHEMA.COLUMNS and creating dynamic SQL queries, but to no avail:
select N'select c.COLUMN_NAME,
(select sum(case when p.' + QUOTENAME(c.COLUMN_NAME) + ' != '''' then 1 else 0 end) from [Produkte] p) [Produkte]
from INFORMATION_SCHEMA.COLUMNS c
where c.TABLE_NAME = ''Produkte'' and c.COLUMN_NAME = ''' + c.COLUMN_NAME + '''' select_statement
from INFORMATION_SCHEMA.COLUMNS c
where c.TABLE_NAME = 'Produkte'
I cannot quite wrap my head around how to combine the two problems (for which I did find solution in their own, but not the combination) of Dynamic Column Names and Count empty values...

Answer 1

You can do something like this using UNPIVOT..
DECLARE #TableName NVARCHAR(MAX) = N'Produkte',
#CountColumns NVARCHAR(MAX),
#Columns NVARCHAR(MAX),
#Sql NVARCHAR(MAX)
SELECT #CountColumns = COALESCE(#CountColumns + ',', '') + 'COUNT(NULLIF(' + QUOTENAME(c.COLUMN_NAME) + ','''')) AS ' + QUOTENAME(c.COLUMN_NAME),
#Columns = COALESCE(#Columns + ',', '') + QUOTENAME(c.COLUMN_NAME)
FROM INFORMATION_SCHEMA.COLUMNS c
WHERE c.TABLE_NAME = #TableName
SET #SQL = 'SELECT [Column Name], [Values]
FROM (
SELECT '
+ #CountColumns + '
FROM ' + #TableName + '
) t
UNPIVOT (
[Values]
FOR [Column Name] IN (' + #Columns + ')
) up
'
EXEC(#SQL)
SQL Fiddle Demo

Answer 2

You can use a dynamic UNPIVOT.
Using these variables:
DECLARE #qry NVARCHAR(MAX)
DECLARE #cols NVARCHAR(MAX) = ''
you can select columns names in a format suitable for the UNPIVOT operation with the following dynamic sql:
SELECT #cols = STUFF((SELECT ',[' + c.COLUMN_NAME + ']'
FROM INFORMATION_SCHEMA.COLUMNS c
WHERE c.TABLE_NAME = 'Produkte'
FOR XML PATH('')), 1, 1, '')
Finally use #cols to build the query:
SET #qry = 'SELECT t.Col, COUNT(*)
FROM (SELECT Val, Col
FROM Produkte
UNPIVOT (
Val FOR Col IN (' + #cols + ')) unpvt
) AS t
WHERE t.Val <> '''' OR t.Val IS NOT NULL
GROUP BY t.Col'
... and execute it to get desired result:
EXEC(#qry)

Answer 3

Ultimately the SQL you are after is something like this:
SELECT ColumnName, NonEmpty
FROM ( SELECT A = 1,
[Col1] = COUNT(CASE WHEN [Col1] <> '' THEN 1 END),
[Col2] = COUNT(CASE WHEN [Col2] <> '' THEN 1 END),
[Col3] = COUNT(CASE WHEN [Col3] <> '' THEN 1 END),
[dkasldk] = COUNT(CASE WHEN [dkasldk] <> '' THEN 1 END),
[dD? d3# !(] = COUNT(CASE WHEN [dD? d3# !(] <> '' THEN 1 END)
FROM #T
) AS t
UNPIVOT
( NonEmpty
FOR ColumnName IN ([Col1],[Col2],[Col3],[dkasldk],[dD? d3# !(])
) AS upvt;
UNPIVOT Will convert your data from
Col1 Col2 Col3
-------------------------
1 3 2
To the format you require:
ColumnName NonEmpty
-------------------------
Col1 1
Col2 3
Col3 2
You can build up dynamically using something like this:
-- SAMPLE DATA
USE TempDB;
CREATE TABLE #T
(
[Col1] VARCHAR(1),
[Col2] VARCHAR(1),
[Col3] VARCHAR(2),
[dkasldk] VARCHAR(6),
[dD? d3# !(] VARCHAR(1)
);
INSERT #T ([Col1], [Col2], [Col3], [dkasldk], [dD? d3# !(])
VALUES
('1', NULL, '2', NULL, ''),
('', '2', 'd', 'ddd939', NULL),
('f', 'f', '84', NULL, '');
DECLARE #TableName SYSNAME = '#T';
-- VALID INPUT TABLE
IF OBJECT_ID(#TableName, 'U') IS NULL
AND OBJECT_ID(#TableName, 'V') IS NULL
BEGIN
PRINT 'Invalid table or View';
RETURN
END
-- BUILD DYNAMIC SQL
DECLARE #SQL NVARCHAR(MAX) =
CONCAT('SELECT ColumnName, NonEmpty FROM (SELECT A = 1, ' ,
STUFF(( SELECT CONCAT(',',
QUOTENAME(name),
' = COUNT(CASE WHEN ',
QUOTENAME(Name),
' <> '''' THEN 1 END)')
FROM sys.columns
WHERE [object_id] = OBJECT_ID(#TableName)
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)'), 1, 1, ''),
' FROM ',
#TableName,
') AS t UNPIVOT (NonEmpty FOR ColumnName IN (',
STUFF(( SELECT CONCAT(',', QUOTENAME(name))
FROM sys.columns
WHERE [object_id] = OBJECT_ID(#TableName)
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)'), 1, 1, ''),
')) AS upvt');
-- EXECUTE DYNAMIC SQL
EXECUTE sp_executesql #SQL;