Currently my cursor results produces a #database_name VARCHAR, I am trying to figure out how to get that as a variable that I can use to loop a query through multiple databases. Most of what I can find cursor related is very much the same loop and print that I have.
I have been through so many different methods that this is probably far from my best attempt and I am starting to go backwards
DECLARE
#cursor_db CURSOR
DECLARE
#database_id VARCHAR(10),
#database_name VARCHAR(255);
SET #cursor_db = CURSOR FOR
SELECT database_id, name
FROM sys.databases
WHERE name LIKE 'Company%';
OPEN #cursor_db;
FETCH NEXT FROM #cursor_db INTO #database_id, #database_name;
WHILE ##FETCH_STATUS = 0
BEGIN
PRINT #database_id + ' ' + #database_name
SELECT *
FROM #database_name i
WHERE sys.columns i LIKE '%Orders%'
FETCH NEXT FROM #cursor_db INTO #database_id, #database_name;
END;
CLOSE #cursor_db;
DEALLOCATE #cursor_db;
Try this:
DECLARE #DBNamePattern varchar(50) = 'Company%'
, #ColNamePattern varchar(50) = 'Order%'
;
SELECT
DatabaseName = C.Table_Catalog
, DatabaseID = D.database_id
, SchemaName = C.TABLE_SCHEMA
, TableName = C.Table_Name
, ColName = C.Column_Name
FROM INFORMATION_SCHEMA.COLUMNS C
JOIN sys.databases D ON D.Name = C.TABLE_CATALOG
WHERE
Table_Catalog LIKE #DBNamePattern
AND Column_Name LIKE #ColNamePattern
ORDER BY
DatabaseName
, TableName
In case anyone was wondering the outcome, you can use a concatenated string in a dynamic query:
-- before cursor opens
DECLARE #base_query1 VARCHAR(max);
DECLARE #base_query2 VARCHAR(max);
DECLARE #query VARCHAR(max)
SET #base_query1 = 'SELECT COUNT(*) AS CNT FROM '
SET #base_query2 = '..TableName' -- expected table name
-- inside the loop
SET #query = CONCAT( #base_query1, #database_name, #base_query2 )
EXEC(#query);
Related
Let's say I have a table with the following columns:
"col1", "col2", "col3", "new_col1", "new_col2", "new_col3" ...
I want to display the columns in the following way:
select col1, new_col1, col2, new_col2, col3, new_col3 ...
Is there a select command/keyboard shortcut that I can do that without copy each column in the select command
Thank you
I have a custom procedure mapped to Ctrl+8 shortcut.
It's something like that:
CREATE or ALTER PROC dbo.utl_get_select(
#table sysname,
#alias varchar(10) = 'v'
)
AS
BEGIN
SET NOCOUNT ON;
DECLARE #query varchar(max) = 'SELECT';
SELECT #alias = ISNULL(#alias, 'v')
SELECT #query = #query + ' ' + #alias + '.' + QUOTENAME(c.name)+','
FROM sys.objects t
JOIN sys.columns c ON c.object_id = t.object_id
WHERE t.name = #table
ORDER BY c.column_id ASC;
SELECT #query = LEFT(#query, LEN(#query)-1) + ' ';
SELECT #query + 'FROM dbo.' + #Table + ' ' + #alias;
END;
We could also use STRING_AGG in SQL Server 2017 or newer.
You can also compare columns names to achieve some customised order.
And the result for EXEC dbo.utl_get_select 'users'
SELECT v.[id], v.[login], v.[email], v.[name], v.[last_name] FROM dbo.users v
Here is a script for Insert and Select
DECLARE #String nvarchar(max)='',#Column nvarchar(100),#Insert nvarchar(max), #Select nvarchar(max),#TBL_NAME nvarchar(150)
SET #TBL_NAME = 'TestTable'
DECLARE CURS CURSOR LOCAL FAST_FORWARD FOR
SELECT COLUMN_NAME
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = #TBL_NAME
OPEN CURS
FETCH NEXT FROM CURS INTO #Column
WHILE ##FETCH_STATUS=0
BEGIN
SET #String = #String +'['+#Column+'],'+'['+#Column+'_NEW],'
FETCH NEXT FROM CURS INTO #Column
END
CLOSE CURS
DEALLOCATE CURS
SET #String = SUBSTRING(#String,1,LEN(#String)-1)
SET #Insert = 'INSERT INTO ['+#TBL_NAME+'] ('+#String+')'
SET #Select = 'SELECT '+#String
Select #Insert,#Select
I am writing a stored proc that needs to search a database for all tables that have a certain column name. Once I get a list of tables that have that column I need to update a value in that column. So first I get a list of tables that have a certain column.
SELECT c.name AS 'ColumnName'
,t.name AS 'TableName'
FROM sys.columns c
JOIN sys.tables t ON c.object_id = t.object_id
WHERE c.name LIKE 'company'
ORDER BY TableName
Now that I have a list of tables that need to be updated I need to run a query similar to the following to update the data in each table.
update table1 set company = #newValue where company = #oldvalue
I'm not sure how to go about writing this part. My first thought was to write a dynamic update statement inside of a cursor like:
Declare #newValue
Declare #oldValue
SET #companyCursor = CURSOR FOR
SELECT t.name AS 'TableName'
FROM sys.columns c
JOIN sys.tables t ON c.object_id = t.object_id
WHERE c.name LIKE 'company'
OPEN #companyCursor;
FETCH NEXT FROM #companyCursor INTO #tableName;
WHILE ##FETCH_STATUS = 0
BEGIN
update #tableName set company = #newValue where company = #oldValue
FETCH NEXT FROM #companyCursor INTO INTO #tableName;
END
Is this a good strategy?
I really dislike cursors so even in cases like this where a cursor is a viable solution I like to leverage the system views to avoid looping. You still have to use dynamic sql because object names cannot be parameterized.
Please note that I am guessing the datatype for company here and you can change this easily. Make sure you change the variable definition both in your script AND in the dynamic sql. You entire script could be shortened to something like this.
declare #SQL nvarchar(max) = ''
, #newValue varchar(10) = 'new'
, #oldValue varchar(10) = 'old'
select #SQL = #SQL + 'Update ' + quotename(object_name(c.object_id)) + ' set company = #newValue where company = #oldValue;'
from sys.columns c
where c.name = 'company'
select #SQL
--uncomment the line below when you are satisfied the dynamic sql is correct.
--This dynamic sql is parameterized as much as possible
--exec sp_executesql #SQL, N'#newValue varchar(10), #oldValue varchar(10)', #newValue = #newValue, #oldValue = #oldValue
No the update at the end will not work. You need to use exec (#sql) like this:
declare #sql varchar(4000)
begin
set #sql = 'update ' + #tableName + 'set company = ' + #newValue + 'where company = ' + #oldValue
exec (#sql)
fetch next ...
end
This assumes that #newvalue and #oldvalue are being assigned values somewhere.
I have about 20 views in a database that reference another database, let's call it database A. I need a way to update these views with a script to point to a different database, database B. Is there a way to replace the name of database A in the view with the name of database B using a single tsql script and keep the views intact? I can do a replace and output the views to the query window but I want to execute the ALTER statements that are generated and not have to run the output manually.
Update What I would like to do is similar to this: https://stackoverflow.com/a/2983927/6084613 but also have the output executed by the script. Is that possible?
I have created below SQL to do the same. this script will take 2 input
1. Old DB Name
2. New DB Name
3. List of view you want to modify
declare #OldDb varchar(250), #newDB varchar(250)
select #OldDb = '' , ---------->>> provide old db name
#newDB = '' ---------->>> provide new db name
create table #ViewList (Id int identity , ViewName varchar(250))
insert into #ViewList
select TABLE_NAME from INFORMATION_SCHEMA.VIEWS where TABLE_NAME IN ( ) ---------->>> provide you view list
create table #ViewDef( ViewDef nvarchar(max) , ViewName varchar(250) ,Id int )
declare #minId int , #maxid int , #sql nvarchar(max) ='' , #ViewName varchar(250)
select #minId = min(Id) , #maxid = max(id) from #ViewList
while #minId <= #maxid
begin
select #ViewName = ViewName from #ViewList where id = #minId
set #sql = ' insert into #ViewDef (ViewDef)
exec sp_helptext '+ #ViewName +'
update #ViewDef
set ViewName = '''+ #ViewName +''',
id = ' + cast(#minId as varchar(10)) +'
where id is null
update #ViewDef
set ViewDef = replace(ViewDef , '''+ #OldDb+''','''+ #newDB +''')
where id = ' + cast(#minId as varchar(10)) +'
update #ViewDef
set ViewDef = replace(ViewDef , ''create'',''alter'')
where id = ' + cast(#minId as varchar(10)) +'
'
exec sp_executesql #sql
SET #sql = ''
select #sql = #sql + ViewDef from #ViewDef where id = #minId
exec sp_executesql #sql
--print #sql
set #minId = #minId +1
end
**Please test the script and save you old definition to avoid any loss in case of any bug in above scrip
You just need to put your query definition into a variable and then execute with sp_executeSQL.
BUT: I'd be cautious using the referenced script without more work.
For example, not all views have the exact text 'CREATE VIEW'.
If hand written , some might be ' CREATE VIEW' or 'CREATE VIEW' for example.
Also, 'DB1' might me written '[DB1]'.
So either add a lot more sophisticated logic, or validated everything by eye before exectuting.
Declare #queryDef nvarchar(max)
SELECT #queryDef = REPLACE (REPLACE (sm.definition, 'CREATE VIEW', 'ALTER VIEW'), 'DB1.', 'DB2.')
FROM sys.sql_modules sm JOIN sys.objects o
ON sm.object_id = o.object_id
WHERE
sm.definition LIKE '%DB1.%' AND o.type = 'V'
print #queryDef
exec sp_executeSql #querydef
Using SimonB idea, I created a loop to do it automatically:
DECLARE #queryDef NVARCHAR(max)
WHILE EXISTS (
SELECT 1
FROM sys.sql_modules sm
JOIN sys.objects o ON sm.object_id = o.object_id
WHERE sm.definition LIKE '%TEXT_TO_REPLACE%'
AND o.type = 'V'
)
BEGIN
-- TO ALTER THE VIEW AUTOMATICALLY
SET #queryDef = ( SELECT TOP 1 Replace (Replace (sm.definition, 'CREATE VIEW', 'ALTER VIEW'),
'TEXT_TO_REPLACE',
'NEW_TEXT')
FROM sys.sql_modules sm
JOIN sys.objects o ON sm.object_id = o.object_id
WHERE sm.definition LIKE '%TEXT_TO_REPLACE%'
AND o.type = 'V')
EXEC sp_executeSql #queryDef
END
I did this. But unfortunately that return all in many table. I want to return all in one unique table. Maybe using "UNION" but I don't know the way to do.
This is my code:
EXEC sp_msforeachdb 'select ''?''AS "DataBase", s.name, t.name AS "Tables",max(si.rows) as "Rows Line"
from [?].sys.tables t inner join [?].sys.schemas s
on t.schema_id = s.schema_id
inner join [?].sys.partitions si on t.object_id = si.object_id
where t.name like "%ATTACH" group by s.name,t.name'`
You cannot do it in a single query.
You could query the sys.databases table to get a temporary table of all your databases, and then run a dynamic query on each database to store the results of the query in your question all in another temporary table.
Then at the end, you just select all rows from the last temporary table.
I have found finally a solution.i just used a Stored Procedures for having the result i was looking for.So decided to post the answer here maybe that will help someone else.
DECLARE #banco_nome nvarchar(MAX), #tabela_nome nvarchar(MAX)
DECLARE #banco_cursor CURSOR
DECLARE #sqlstatement nvarchar(MAX)
DECLARE #count_sql nvarchar(MAX)
DECLARE #total int
DECLARE #RegistrosFotograficos TABLE
(
DatabaseName nvarchar(max),
TableName nvarchar(max),
Total int
)
SET #banco_cursor = CURSOR FORWARD_ONLY FOR
SELECT name FROM sys.databases
OPEN #banco_cursor
FETCH NEXT FROM #banco_cursor INTO #banco_nome
WHILE ##FETCH_STATUS = 0
BEGIN
SET #sqlstatement = 'DECLARE tabela_cursor CURSOR FORWARD_ONLY FOR SELECT TABLE_NAME FROM ' + #banco_nome + '.INFORMATION_SCHEMA.TABLES WHERE TABLE_TYPE = ''BASE TABLE'' AND TABLE_NAME LIKE ''%ATTACH'' ORDER BY TABLE_NAME'
EXEC sp_executesql #sqlstatement
OPEN tabela_cursor
FETCH NEXT FROM tabela_cursor INTO #tabela_nome
WHILE ##FETCH_STATUS = 0
BEGIN
SET #count_sql = 'USE ' + #banco_nome + '; SELECT #total=COUNT(1) FROM ' + #tabela_nome;
EXECUTE sp_executesql #count_sql, N'#total int OUTPUT', #total=#total OUTPUT
INSERT INTO #RegistrosFotograficos (DatabaseName, TableName, Total) VALUES (#banco_nome, #tabela_nome, #total);
FETCH NEXT FROM tabela_cursor INTO #tabela_nome
END
CLOSE tabela_cursor;
DEALLOCATE tabela_cursor;
FETCH NEXT FROM #banco_cursor INTO #banco_nome
END
CLOSE #banco_cursor;
DEALLOCATE #banco_cursor;
SELECT * FROM #RegistrosFotograficos
This will list all the tables in a given database and the number of rows in each. Notice the results are in a table named #results:
set nocount on
declare #curtable sysname
declare #prevtable sysname
declare #curcount int
declare #tsql varchar(500)
if object_ID('tempdb..#curtables','U') is not null
drop table #curtables
select name into #curtables
from sys.objects
where type='U'
order by 1
if object_id('tempdb..#results','U') is not null
drop table #results
create table #results(name sysname,numrows int)
select top 1 #curtable=name from #curtables order by name
while (1=1)
begin
set #tsql = 'select '''+quotename(#curtable) +''',count(*) numrows from '+quotename(#curtable)
print #tsql
insert into #results
exec (#tsql)
set #prevtable= #curtable
select top 1 #curtable = name
from #curtables
where name > #prevtable
order by name
if #curtable=#prevtable
break
end
How do I select all the columns in a table that only contain NULL values for all the rows? I'm using MS SQL Server 2005. I'm trying to find out which columns are not used in the table so I can delete them.
Here is the sql 2005 or later version: Replace ADDR_Address with your tablename.
declare #col varchar(255), #cmd varchar(max)
DECLARE getinfo cursor for
SELECT c.name FROM sys.tables t JOIN sys.columns c ON t.Object_ID = c.Object_ID
WHERE t.Name = 'ADDR_Address'
OPEN getinfo
FETCH NEXT FROM getinfo into #col
WHILE ##FETCH_STATUS = 0
BEGIN
SELECT #cmd = 'IF NOT EXISTS (SELECT top 1 * FROM ADDR_Address WHERE [' + #col + '] IS NOT NULL) BEGIN print ''' + #col + ''' end'
EXEC(#cmd)
FETCH NEXT FROM getinfo into #col
END
CLOSE getinfo
DEALLOCATE getinfo
SELECT cols
FROM table
WHERE cols IS NULL
This should give you a list of all columns in the table "Person" that has only NULL-values. You will get the results as multiple result-sets, which are either empty or contains the name of a single column. You need to replace "Person" in two places to use it with another table.
DECLARE crs CURSOR LOCAL FAST_FORWARD FOR SELECT name FROM syscolumns WHERE id=OBJECT_ID('Person')
OPEN crs
DECLARE #name sysname
FETCH NEXT FROM crs INTO #name
WHILE ##FETCH_STATUS = 0
BEGIN
EXEC('SELECT ''' + #name + ''' WHERE NOT EXISTS (SELECT * FROM Person WHERE ' + #name + ' IS NOT NULL)')
FETCH NEXT FROM crs INTO #name
END
CLOSE crs
DEALLOCATE crs
Or did you want to just see if a column only has NULL values (and, thus, is probably unused)?
Further clarification of the question might help.
EDIT:
Ok.. here's some really rough code to get you going...
SET NOCOUNT ON
DECLARE #TableName Varchar(100)
SET #TableName='YourTableName'
CREATE TABLE #NullColumns (ColumnName Varchar(100), OnlyNulls BIT)
INSERT INTO #NullColumns (ColumnName, OnlyNulls) SELECT c.name, 0 FROM syscolumns c INNER JOIN sysobjects o ON c.id = o.id AND o.name = #TableName AND o.xtype = 'U'
DECLARE #DynamicSQL AS Nvarchar(2000)
DECLARE #ColumnName Varchar(100)
DECLARE #RC INT
SELECT TOP 1 #ColumnName = ColumnName FROM #NullColumns WHERE OnlyNulls=0
WHILE ##ROWCOUNT > 0
BEGIN
SET #RC=0
SET #DynamicSQL = 'SELECT TOP 1 1 As HasNonNulls FROM ' + #TableName + ' (nolock) WHERE ''' + #ColumnName + ''' IS NOT NULL'
EXEC sp_executesql #DynamicSQL
set #RC=##rowcount
IF #RC=1
BEGIN
SET #DynamicSQL = 'UPDATE #NullColumns SET OnlyNulls=1 WHERE ColumnName=''' + #ColumnName + ''''
EXEC sp_executesql #DynamicSQL
END
ELSE
BEGIN
SET #DynamicSQL = 'DELETE FROM #NullColumns WHERE ColumnName=''' + #ColumnName+ ''''
EXEC sp_executesql #DynamicSQL
END
SELECT TOP 1 #ColumnName = ColumnName FROM #NullColumns WHERE OnlyNulls=0
END
SELECT * FROM #NullColumns
DROP TABLE #NullColumns
SET NOCOUNT OFF
Yes, there are easier ways, but I have a meeting to go to right now. Good luck!
Here is an updated version of Bryan's query for 2008 and later. It uses INFORMATION_SCHEMA.COLUMNS, adds variables for the table schema and table name. The column data type was added to the output. Including the column data type helps when looking for a column of a particular data type. I didn't added the column widths or anything.
For output the RAISERROR ... WITH NOWAIT is used so text will display immediately instead of all at once (for the most part) at the end like PRINT does.
SET NOCOUNT ON;
DECLARE
#ColumnName sysname
,#DataType nvarchar(128)
,#cmd nvarchar(max)
,#TableSchema nvarchar(128) = 'dbo'
,#TableName sysname = 'TableName';
DECLARE getinfo CURSOR FOR
SELECT
c.COLUMN_NAME
,c.DATA_TYPE
FROM
INFORMATION_SCHEMA.COLUMNS AS c
WHERE
c.TABLE_SCHEMA = #TableSchema
AND c.TABLE_NAME = #TableName;
OPEN getinfo;
FETCH NEXT FROM getinfo INTO #ColumnName, #DataType;
WHILE ##FETCH_STATUS = 0
BEGIN
SET #cmd = N'IF NOT EXISTS (SELECT * FROM ' + #TableSchema + N'.' + #TableName + N' WHERE [' + #ColumnName + N'] IS NOT NULL) RAISERROR(''' + #ColumnName + N' (' + #DataType + N')'', 0, 0) WITH NOWAIT;';
EXECUTE (#cmd);
FETCH NEXT FROM getinfo INTO #ColumnName, #DataType;
END;
CLOSE getinfo;
DEALLOCATE getinfo;
You can do:
select
count(<columnName>)
from
<tableName>
If the count returns 0 that means that all rows in that column all NULL (or there is no rows at all in the table)
can be changed to
select
case(count(<columnName>)) when 0 then 'Nulls Only' else 'Some Values' end
from
<tableName>
If you want to automate it you can use system tables to iterate the column names in the table you are interested in
If you need to list all rows where all the column values are NULL, then i'd use the COLLATE function. This takes a list of values and returns the first non-null value. If you add all the column names to the list, then use IS NULL, you should get all the rows containing only nulls.
SELECT * FROM MyTable WHERE COLLATE(Col1, Col2, Col3, Col4......) IS NULL
You shouldn't really have any tables with ALL the columns null, as this means you don't have a primary key (not allowed to be null). Not having a primary key is something to be avoided; this breaks the first normal form.
Try this -
DECLARE #table VARCHAR(100) = 'dbo.table'
DECLARE #sql NVARCHAR(MAX) = ''
SELECT #sql = #sql + 'IF NOT EXISTS(SELECT 1 FROM ' + #table + ' WHERE ' + c.name + ' IS NOT NULL) PRINT ''' + c.name + ''''
FROM sys.objects o
JOIN sys.columns c ON o.[object_id] = c.[object_id]
WHERE o.[type] = 'U'
AND o.[object_id] = OBJECT_ID(#table)
AND c.is_nullable = 1
EXEC(#sql)
Not actually sure about 2005, but 2008 ate it:
USE [DATABASE_NAME] -- !
GO
DECLARE #SQL NVARCHAR(MAX)
DECLARE #TableName VARCHAR(255)
SET #TableName = 'TABLE_NAME' -- !
SELECT #SQL =
(
SELECT
CHAR(10)
+'DELETE FROM ['+t1.TABLE_CATALOG+'].['+t1.TABLE_SCHEMA+'].['+t1.TABLE_NAME+'] WHERE '
+(
SELECT
CASE t2.ORDINAL_POSITION
WHEN (SELECT MIN(t3.ORDINAL_POSITION) FROM INFORMATION_SCHEMA.COLUMNS t3 WHERE t3.TABLE_NAME=t2.TABLE_NAME) THEN ''
ELSE 'AND '
END
+'['+COLUMN_NAME+'] IS NULL' AS 'data()'
FROM INFORMATION_SCHEMA.COLUMNS t2 WHERE t2.TABLE_NAME=t1.TABLE_NAME FOR XML PATH('')
) AS 'data()'
FROM INFORMATION_SCHEMA.TABLES t1 WHERE t1.TABLE_NAME = #TableName FOR XML PATH('')
)
SELECT #SQL -- EXEC(#SQL)
Here I have created a script for any kind of SQL table. please copy this stored procedure and create this on your Environment and run this stored procedure with your Table.
exec [dbo].[SP_RemoveNullValues] 'Your_Table_Name'
stored procedure
GO
/****** Object: StoredProcedure [dbo].[SP_RemoveNullValues] Script Date: 09/09/2019 11:26:53 AM ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
-- akila liyanaarachchi
Create procedure [dbo].[SP_RemoveNullValues](#PTableName Varchar(50) ) as
begin
DECLARE Cussor CURSOR FOR
SELECT COLUMN_NAME,TABLE_NAME,DATA_TYPE
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = #PTableName
OPEN Cussor;
Declare #ColumnName Varchar(50)
Declare #TableName Varchar(50)
Declare #DataType Varchar(50)
Declare #Flage int
FETCH NEXT FROM Cussor INTO #ColumnName,#TableName,#DataType
WHILE ##FETCH_STATUS = 0
BEGIN
set #Flage=0
If(#DataType in('bigint','numeric','bit','smallint','decimal','smallmoney','int','tinyint','money','float','real'))
begin
set #Flage=1
end
If(#DataType in('date','atetimeoffset','datetime2','smalldatetime','datetime','time'))
begin
set #Flage=2
end
If(#DataType in('char','varchar','text','nchar','nvarchar','ntext'))
begin
set #Flage=3
end
If(#DataType in('binary','varbinary'))
begin
set #Flage=4
end
DECLARE #SQL VARCHAR(MAX)
if (#Flage in(1,4))
begin
SET #SQL =' update ['+#TableName+'] set ['+#ColumnName+']=0 where ['+#ColumnName+'] is null'
end
if (#Flage =3)
begin
SET #SQL =' update ['+#TableName+'] set ['+#ColumnName+'] = '''' where ['+#ColumnName+'] is null '
end
if (#Flage =2)
begin
SET #SQL =' update ['+#TableName+'] set ['+#ColumnName+'] ='+'''1901-01-01 00:00:00.000'''+' where ['+#ColumnName+'] is null '
end
EXEC(#SQL)
FETCH NEXT FROM Cussor INTO #ColumnName,#TableName,#DataType
END
CLOSE Cussor
DEALLOCATE Cussor
END
You'll have to loop over the set of columns and check each one. You should be able to get a list of all columns with a DESCRIBE table command.
Pseudo-code:
foreach $column ($cols) {
query("SELECT count(*) FROM table WHERE $column IS NOT NULL")
if($result is zero) {
# $column contains only null values"
push #onlyNullColumns, $column;
} else {
# $column contains non-null values
}
}
return #onlyNullColumns;
I know this seems a little counterintuitive but SQL does not provide a native method of selecting columns, only rows.
I would also recommend to search for fields which all have the same value, not just NULL.
That is, for each column in each table do the query:
SELECT COUNT(DISTINCT field) FROM tableName
and concentrate on those which return 1 as a result.
SELECT t.column_name
FROM user_tab_columns t
WHERE t.nullable = 'Y' AND t.table_name = 'table name here' AND t.num_distinct = 0;
An updated version of 'user2466387' version, with an additional small test which can improve performance, because it's useless to test non nullable columns:
AND IS_NULLABLE = 'YES'
The full code:
SET NOCOUNT ON;
DECLARE
#ColumnName sysname
,#DataType nvarchar(128)
,#cmd nvarchar(max)
,#TableSchema nvarchar(128) = 'dbo'
,#TableName sysname = 'TableName';
DECLARE getinfo CURSOR FOR
SELECT
c.COLUMN_NAME
,c.DATA_TYPE
FROM
INFORMATION_SCHEMA.COLUMNS AS c
WHERE
c.TABLE_SCHEMA = #TableSchema
AND c.TABLE_NAME = #TableName
AND IS_NULLABLE = 'YES';
OPEN getinfo;
FETCH NEXT FROM getinfo INTO #ColumnName, #DataType;
WHILE ##FETCH_STATUS = 0
BEGIN
SET #cmd = N'IF NOT EXISTS (SELECT * FROM ' + #TableSchema + N'.' + #TableName + N' WHERE [' + #ColumnName + N'] IS NOT NULL) RAISERROR(''' + #ColumnName + N' (' + #DataType + N')'', 0, 0) WITH NOWAIT;';
EXECUTE (#cmd);
FETCH NEXT FROM getinfo INTO #ColumnName, #DataType;
END;
CLOSE getinfo;
DEALLOCATE getinfo;
You might need to clarify a bit. What are you really trying to accomplish? If you really want to find out the column names that only contain null values, then you will have to loop through the scheama and do a dynamic query based on that.
I don't know which DBMS you are using, so I'll put some pseudo-code here.
for each col
begin
#cmd = 'if not exists (select * from tablename where ' + col + ' is not null begin print ' + col + ' end'
exec(#cmd)
end