Alter All Data Types To Different Data Type I have a database that has multiple tables with datetime2 fields.  I need to convert all of these to datetime fields.  I ran this syntax that produced over 300 tables that need to be altered with roughly 1200 fields.  

select
    so.name table_name
   ,sc.name column_name
   ,st.name data_type
from sysobjects so
inner join syscolumns sc on (so.id = sc.id)
inner join systypes st on (st.type = sc.type)
where so.type = 'U'
and st.name IN ('DATETIME2')
ORDER BY so.name ASC


Now, for speed, I thought I would write some syntax to do this for me, but I must have set-up something incorrectly as I allowed this to run for 30 minutes and it was still running.  If I run the print statements everything prints out as it should (at least to my semi-trained eye).  Is > 30 minutes acceptable time for these alter table statements to complete or is something slowing me down/should I not use a cursor?

Declare @sql nvarchar(max), @tablename varchar(100), @fieldname varchar(100)

Select 
table_name
,column_name
FROM #Helper
Order by table_name asc

DECLARE cursor1 CURSOR FOR

Select
table_name
,column_name
FROM #Helper
ORDER BY table_name asc

OPEN cursor1

FETCH NEXT FROM cursor1 INTO @tablename, @fieldname

WHILE @@FETCH_STATUS = 0
BEGIN

Set @SQL = 'Alter Table '+@tablename+' Alter Column '+@fieldname+' datetime'
PRINT @SQL
--EXEC sp_executesql @sql;
FETCH NEXT FROM cursor1 INTO @tablename, @fieldname

END

CLOSE cursor1

DEALLOCATE cursor1

DROP TABLE #Helper


EDIT
I let the statement run a bit longer and discovered that it is actually hitting an error with one of the constraints that (could or could not) be causing the process to take so long.  I am trying to run this statement

Alter Table TestTable Alter Column datecreate datetime


And this error message is thrown:


  Msg 5074, Level 16, State 1, Line 1
  The object 'DF__Test_Table___datec__0D7A0286' is dependent on column 'datecreate'.
  Msg 4922, Level 16, State 9, Line 1
  ALTER TABLE ALTER COLUMN datecreate failed because one or more objects access this column.


Now if I script constraint as - create to this is the output that is generated:

ALTER TABLE [dbo].[TestTable] ADD  DEFAULT (getdate()) FOR [datecreate]


Nothing in there (to me) seems to be keeping this column as a datetime2 data type.  Do I need to add an extra check in my syntax to determine if the column has a constraint, and if it does, then drop the constraint and add it back?
Changing datetime2 to datetime is a fundamental data type change. Each ALTER will update every row in the specified table.  This can take a while depending on the size of your tables, especially if your largest tables have many datetime2 columns. Also, if there is any other concurrent activity, the DDL will be blocked by other activity.