I want to alter column within the table to be NULL from NOT NULL.
The problem is that table has one constraint, one trigger and 4 indexes.
Can I somehow alter that column without dropping and recreating everything?
exec sys.sp_depends 'object_name'
List all dependencies and then drop them an recreate everything.
SQL Managements studio offer option with SCRIPT AS CREATE and you can save all views, triggers, tables as backup...
Related
I want to alter all varchar columns in my database to nvarchar, using a T-SQL script.
There are a lot of dependencies (keys, constraints, and views) that cause problems when trying to alter.
The object 'X' is dependent on column 'Y'. ALTER TABLE ALTER COLUMN 'Y' failed because one or more objects access this column.
My unsuccessful attempts: forcing a change with PowerShell, and creating a generate script for the whole database and using that to create a copy with all the changes I need. These attempts didn't work, because I lost the table data and the generate scripts were too big for any program to handle.
How does one create all DROP and CREATE scripts of the objects that cause problems when trying to alter to make the changes and recreate the database schema like it was before altering?
In postgres when I drop a table it is dropping all views that depend upon it. Is there a way to persist the views so that they dont get dropped
Note: the table will be regenerated on daily basis with new data.
From PostgreSQL documentation
DROP TABLE always removes any indexes, rules, triggers, and constraints that exist for the target table. However, to drop a table that is referenced by a view or a foreign-key constraint of another table, CASCADE must be specified. (CASCADE will remove a dependent view entirely, but in the foreign-key case it will only remove the foreign-key constraint, not the other table entirely.)
Try TRUNCATE TABLE / CREATE TABLE IF NOT EXISTS instead of DROP.
I'm trying to create and increment by one some values to put into an already existing (but empty) column. I'm currently using the identity function, but I wouldn't mind using a custom made function. Right now, SSMS is saying there's incorrect syntax near IDENTITY. Could anybody help me fix this syntax?
ALTER Table anthemID IDENTITY(1,1)
First, you can't make a column identity after the fact: it has to be set that way at creation time.
Second, I'm not quite sure what you mean by "increment the value of an already existing column by one." You can only increment the value of rows within a column--perform a DML (Data Modification Language) query. The script you suggested above is a DDL (Data Definition Language) query that actually modifies the structure of the table, affecting the entire column--all rows.
If you just want to increment all the rows by 1, you'd do this:
UPDATE dbo.YourTable SET anthemID = anthemID + 1;
On the other hand, if you want the anthemID column to acquire the identity property so that new inserts to the table receive unique, autoincrementing values, you can do that with some juggling:
Back up your database and confirm it is a good backup.
Script out your table including all constraints.
Drop all constraints on your table or other tables that involve anthemID.
ALTER TABLE dbo.YourTable DROP CONSTRAINT PK_YourTable -- if part of PK
ALTER TABLE dbo.AnotherTable DROP CONSTRAINT FK_AnotherTable_anthemID -- FKs
Rename your table
EXEC sp_rename 'dbo.YourTable', 'YourTableTemp';
Modify the script you generated above to make anthemID identity (add in identity(1,1) after int);
Run the modified script to create a new table with the same name as the original.
Insert the data from the old table to the new one:
SET IDENTITY_INSERT dbo.YourTable ON;
INSERT dbo.YourTable (anthemID, AnotherColumn, RestOfColumns)
SELECT anthemID, AnotherColumn, RestOfColumns
FROM dbo.YourTableTemp;
SET IDENTITY_INSERT dbo.YourTable OFF;
Re-add all constraints that were dropped.
Drop the original, renamed table after confirming you don't need the data any more.
You may be able to do this from SSMS's GUI table designer, and it will take care of moving the data over for you. However, this has bitten some people in the past and if you don't have a good database backup, well, don't do it because you might encounter some regret in the process.
UPDATE
Now that I know the column is blank, it's even easier.
ALTER TABLE dbo.YourTable DROP COLUMN anthemID;
ALTER TABLE dbo.YourTable ADD anthemID int identity(1,1) NOT NULL;
This does have the drawback of moving the column to the end of the table. If that's a problem, you can follow much the same procedure as I outlined above (to fix things yourself, or alternately use the designer in SQL Server Management Studio).
I recommend in the strongest terms possible that you use an identity column and do not try to create your own means of making new rows get an incremented value.
For emphasis, I'll quote #marc_s's comment above:
The SELECT MAX(ID)+1 approach is highly unsafe in a concurrent environment - in a system under some load, you will get duplicates. Don't do this yourself - don't try to reinvent the wheel - use the proper mechanisms (here: IDENTITY) that your database gives you and let the database handle all the nitty-gritty details!
I wholeheartedly agree with him.
I am busy studying MySQL and I understand that update is used to update a record or row in a table. So what does alter do that is so different? Seems like they are the same.
Thanks, any help will be appreciated.
ALTER is a DDL (Data Definition Language) statement. Whereas UPDATE is a DML (Data Manipulation Language) statement. ALTER is used to update the structure of the table (add/remove field/index etc). Whereas UPDATE is used to update data.
The ALTER changes the table in the database, you can add or remove columns, etc. But it does not change data (except in the dropped or added columns of course).
While the UPDATE changes the rows in the table, and leaves the table unchanged.
ALTER is used to change things like table structures or stored procs, otherwise known as DDL statements.
ALTER table MyTable
ADD MyNewColumn VARCHAR(100)
OR
ALTER PROC dbo.MyStoredProc
Alter command is a data definition language
Update command is a data manipulation language
Alter example- table structure, table name, sp, functions
Update example-change database in a row or column etc
Alter command make changes in table structure.
Update command make changes with inside the table
Alter command is used to add, delete modify the attributes of the table in the database
Update command is used to update existing record in a database
Let's see in simple words...
Alter command we use for the modify the structure of the database, table(add, drop, modify)and it falls under DDL.
Update command we use for the modify the rows(records) of the table using where condition and its fall under DML.
I right click on my table in ssms 2008 and select Script Table as / Drop and Create Table to new window and I try to run the script but get an error:
Could not drop table because it is referenced by a foreign key constraint
What was the point of the Drop and Create generate script then?
Thanks,
rod.
The point of the Drop and Create generate script is exactly what you'd think - it gives you an easy way to script out dropping and re-creating a table. However you can't drop a table if other tables reference it via foreign key constraints, which is why you're getting the error message.
If you're just trying to add a column, you can right-click the table in Enterprise Manager and click Modify and just add the column in design view. There's no need to drop the table just to add a column. (And it's especially an awful approach if the table has data in it.)
The easiest way to add a column to an existing table? Write the ALTER TABLE statement yourself instead of relying on SQL Server Management Studio to do it for you:
ALTER TABLE YourTableName
ADD ColumnName int