Stored procedure to drop the column in SQL Server - sql

Question

I created many tables and I have noticed that I have created one useless column in all the tables. I want to create a stored procedure which will drop one specific column and can be useful in all the column.
I created this stored procedure but I'm getting an error. Help me please

Answer 1

You cannot parametrize table and column names with parameters - those are only valid for values - not for object names.
If this is a one-time operation, the simplest option would be to generate the ALTER TABLE ... DROP COLUMN ... statements in SSMS using this code:
SELECT
'ALTER TABLE ' + SCHEMA_NAME(t.schema_id) + '.' + t.Name +
' DROP COLUMN Phone;'
FROM
sys.tables t
and then execute this code in SSMS; the output from it is a list of statement which you can then copy & paste to a new SSMS window and execute.
If you really want to do this as a stored procedure, you can apply the same basic idea - and then just use code (a cursor) to iterate over the commands being generated, and executing them - something like this:
CREATE PROCEDURE dbo.DropColumnFromAllTables (#ColumnName NVARCHAR(100))
AS
BEGIN
DECLARE #SchemaName sysname, #TableName sysname
-- define cursor over all tables which contain this column in question
DECLARE DropCursor CURSOR LOCAL FAST_FORWARD
FOR
SELECT
SchemaName = s.Name,
TableName = t.Name
FROM
sys.tables t
INNER JOIN
sys.schemas s ON t.schema_id = s.schema_id
WHERE
EXISTS (SELECT * FROM sys.columns c
WHERE c.object_id = t.object_id
AND c.Name = #ColumnName);
-- open cursor and start iterating over the tables found
OPEN DropCursor
FETCH NEXT FROM DropCursor INTO #SchemaName, #TableName
WHILE ##FETCH_STATUS = 0
BEGIN
DECLARE #Stmt NVARCHAR(1000)
-- generate the SQL statement
SET #Stmt = N'ALTER TABLE [' + #SchemaName + '].[' + #TableName + '] DROP COLUMN [' + #ColumnName + ']';
-- execute that SQL statement
EXEC sp_executeSql #Stmt
FETCH NEXT FROM DropCursor INTO #SchemaName, #TableName
END
CLOSE DropCursor
DEALLOCATE DropCursor
END

Answer 2

This procedure should work.
It loops through all cols and then deletes the column where sum(col) is zero.
Take a Backup of the Table
alter procedure deletecolumnsifzero #tablename varchar(1000)
as
set nocount on
declare #n int
declare #sql nvarchar(1000)
declare #sum_cols nvarchar(1000)
declare #c_id nvarchar(100)
set #n = 0
declare c1 cursor for
select column_name from information_schema.columns
where
table_name like #tablename
--Cursor Starts
open c1
fetch next from c1
into #c_id
while ##fetch_status = 0
begin
set #sql=''
set #sql='select #sum_cols = sum('+#c_id+') from ['+#tablename+']'
exec sp_Executesql #sql,N'#sum_cols int out,#tablename nvarchar(100)',#sum_cols out,#tablename
if(#sum_cols = 0)
begin
set #n=#n+1
set #sql=''
set #sql= #sql+'alter table ['+#tablename+'] drop column ['+#c_id+']'
exec sp_executesql #sql
end
fetch next from c1
into #c_id
end
close c1
deallocate c1