Dynamically Count Null Values in SQL Server - sql

Question

I'm a little new at SQL so please bear with me. I am attempting to write some a query that will allow me to loop through an entire table and find the number of times null values appear in each column. This is easy to do the hard way by typing the following:
Select
SUM(CASE COL_1 WHEN IS NULL THEN 1 ELSE 0 END) AS COL_1_NULLS
,SUM(CASE COL_2 WHEN IS NULL THEN 1 ELSE 0 END) AS COL_2_NULLS
FROM TABLE1
This is easy but it can become arduous if you want to do this for multiple tables or if a single table has a lot of columns.
I'm looking for a way to write a query that passes a table name into it and then loops through each column in the defined table (possibly pulling the column name by ordinance via a join to a metadata view?) and then sums the number of nulls in the column. Before anyone jumps on the nitpick bandwagon please keep in mind that this basic idea could be used for more than just finding nulls. Any assistance with this issue is greatly appreciated.

Answer 1

You need to use dynamic sql:
declare #custom_sql varchar(max)
set #custom_sql = 'SELECT null as first_row'
select
#custom_sql = #custom_sql + ', ' + 'SUM(CASE WHEN ' + COLUMN_NAME + ' IS NULL THEN 1 ELSE 0 END) as ' + COLUMN_NAME + '_NULLS'
from
INFORMATION_SCHEMA.COLUMNS where table_name = 'MYTABLE'
set #custom_sql = #custom_sql + ' FROM MYTABLE'
exec(#custom_sql)
You can also use the COALESCE term (just for a slightly different approach):
declare #custom_sql varchar(max)
select
#custom_sql = COALESCE(#custom_sql + ', ', '') + 'SUM(CASE WHEN ' + COLUMN_NAME + ' IS NULL THEN 1 ELSE 0 END) as ' + COLUMN_NAME + '_NULLS'
from
INFORMATION_SCHEMA.COLUMNS where table_name = 'users'
set #custom_sql = 'SELECT ' + #custom_sql
set #custom_sql = #custom_sql + ' FROM Users'
print #custom_sql
exec(#custom_sql)

Answer 2

I don't know how to make a generic query, but you can always generate the script like this
declare #sql nvarchar(max) = 'select 1 as dummy'
select #sql = #sql + '
, sum(case when [' + c.name + '] is null then 1 else 0 end) as [' + c.name + '_NULLS]'
from sys.columns c
join sys.tables t on t.object_id = c.object_id
where t.name = 'TABLE1'
set #sql = #sql + ' from TABLE1'
select #sql
Then you can execute the result eg. with exec sp_executesql #sql

Answer 3

For a cooler approach, you can use ISNULL to skip the first comma.
declare #sql nvarchar(max)
declare #tablename nvarchar(255) = 'xxxx'
Select #sql = ISNULL(#SQL + ',','') + ' ' + COLUMN_NAME + '_count = Sum(case when ' + COLUMN_NAME + ' is null then 1 else 0 end)' + char(13)
From information_schema.columns
where table_name = #tablename
set #sql = 'Select' + #sql + ' From ' + #tablename
print #sql
exec sp_executesql #sql