问题
Having a table with 60 columns, and 200 rows. Altering a BIT column from NULL to NOT NULL, now has a running execution time of over 3 hours. Why is this taking so long?
This is the query that I'm execution:
ALTER TABLE tbl
ALTER COLUMN col BIT NOT NULL
Is there a faster way to do it, besides creating a new column, updating it with values from the old column, then dropping the old column and renaming the new one?
This is on MS SQL Server 2005.
回答1:
IS the ALTER blocked by metadata shared locks held by other statements? Any ALTER requires a metadata exclusive lock, and as such will be block by any other statement that uses the table.
Check Activity Monitor, or look into sys.dm_exec_requests and see who's blocking your ALTER INDEX.
回答2:
Is it still running after 3 hours (while you post the question), or completes after 3 hours?
If it's still running run DBCC OPENTRAN: you've probably an open transaction somewhere that has left a schema lock on the table
Or SELECT * FROM sys.sysprocesses WHERE blocked <> 0 gives you what has been blocked
来源：https://stackoverflow.com/questions/2465455/execution-time-of-alter-column