in T-SQL, is it possible to find names of columns

Question

Is it possible in T-SQL to write a proper query reflecting this pseudo-code:

SELECT {primary_key}, {column_name}
FROM {table}
WHERE {any column_name value} is NULL

i.e. without referencing each column-name explicitly.

Sounds simple enough but I've searched pretty extensively and found nothing.

Answer 1

You have to use dynamic sql to solve that problem. I have demonstrated how it could be done. With this sql you can pick a table and check the row with id = 1 for columns being null and primary keys. I included a test table at the bottom of the script. Code will not display anything if there is not primary keys and no columns being null.

DECLARE @table_name VARCHAR(20)
DECLARE @chosencolumn VARCHAR(20)
DECLARE @sqlstring VARCHAR(MAX) 
DECLARE @sqlstring2 varchar(100)
DECLARE @text VARCHAR(8000)
DECLARE @t TABLE (col1 VARCHAR(30), dummy INT)

SET @table_name = 'test_table'  -- replace with your tablename if you want
SET @chosencolumn = 'ID=1'      -- replace with criteria for selected row

SELECT @sqlstring = COALESCE(@sqlstring, '') + 'UNION ALL SELECT '',''''NULL '''' '' + '''+t1.column_name+''', 1000 ordinal_position FROM ['+@table_name+'] WHERE [' +t1.column_name+ '] is null and ' +@chosencolumn+ ' ' 
FROM INFORMATION_SCHEMA.COLUMNS t1
LEFT JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE t2
ON t1.column_name = t2.column_name
AND t1.table_name = t2.table_name
AND t1.table_schema = t2.table_schema
WHERE t1.table_name = @table_name
AND t2.column_name is null

SET @sqlstring = stuff('UNION ALL SELECT '',''''PRIMARY KEY'''' ''+ column_name + '' '' col1, ordinal_position 
FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE
WHERE table_name = ''' + @table_name+ '''' + @sqlstring, 1, 10, '') + 'order by 2'

INSERT @t
EXEC( @sqlstring)

SELECT @text = COALESCE(@text, '') + col1
FROM @t

SET @sqlstring2 ='select '+stuff(@text,1,1,'')

EXEC( @sqlstring2)

Result:

id           host_id      date         col1
PRIMARY KEY  PRIMARY KEY  PRIMARY KEY  NULL

Test table

CREATE TABLE [dbo].[test_table](
    [id] int not null,
    [host_id] [int] NOT NULL,
    [date] [datetime] NOT NULL,
    [col1] [varchar](20) NULL,
    [col2] [varchar](20) NULL,
 CONSTRAINT [PK_test_table] PRIMARY KEY CLUSTERED 
(
    [id] ASC,
    [host_id] ASC,
    [date] ASC
))

Test data

INSERT test_table VALUES (1, 1, getdate(), null, 'somevalue')