Is there a simple way to drop a group of interrelated tables in SQL Server? Ideally I'd like to avoid having to worry about what order they're being dropped in since I know the entire group will be gone by the end of the process.
At the risk of sounding stupid, I don't believe SQL Server supports the delete / cascade syntax. I think you can configure a delete rule to do cascading deletes (http://msdn.microsoft.com/en-us/library/ms152507.aspx), but as far as I know the trick with SQL Server is to just to run your drop query once for each table you're dropping, then check it worked.
I'm not sure, if Derek's approach works. You haven't mark it as best answer yet.
If not: with SQL Server 2005 it should be possible, I guess.
There they introduced exceptions (which I've not used yet). So drop the table, catch the exception, if one occurs and try the next table till they are all gone.
You can store the list of tables in a temp-table and use a cursor to traverse it, if you want to.
A diferent approach could be: first get rid of the constraints, then drop the tables in a single shot.
In other words, a DROP CONSTRAINT for every constraint, then a DROP TABLE for each table; at this point the order of execution shouldn't be an issue.
This requires the sp___drop___constraints script you can find at Database Journal:
sp_MSforeachtable #command1="print 'disabling constraints: ?'", #command2="sp_drop_constraints #tablename=?"
GO
sp_MSforeachtable #command1="print 'dropping: ?'", #command2="DROP TABLE ?"
GO
NOTE this - obviously - if you meant to drop ALL of the tables in your database, so be careful
I don't have access to SQL Server to test this, but how about:
DROP TABLE IF EXISTS table1, table2, table3 CASCADE;
I ended up using Apache's ddlutils to perform the dropping for me, which sorted it out in my case, though a solution which worked only within sql server would be quite a bit simpler.
#Derek Park, I didn't know you could comma separate tables there, so that's handy, but it doesn't seem to work quite as expected. Nether IF EXISTS nor CASCADE are recognised by sql server it seems, and running drop table X, Y, Z seems to work only if they should be dropped in the stated order.
See also http://msdn.microsoft.com/en-us/library/ms173790.aspx, which describes the drop table syntax.
The thing holding you back from dropping the tables in any order are foreign key dependencies between the tables. So get rid of the FK's before you start.
Using the INFORMATION_SCHEMA system views, retrieve a list of all foreign keys related to any of these tables
Drop each of these foreign keys
Now you should be able to drop all of the tables, using any order that you want.
Related
Is there a standard SQL command that when a table is to be dropped, it drops all the views on it as well?
No, there is no standard way to drop a table and all associated views. I know Postgres has a CASCADE option but that's implementation specific - MySQL accepts CASCADE but does absolutely nothing with it.
There is not a standardized command across all rdms that will drop a table and it's bounded view(s) in one operation.
Is there a way to prevent DROP TABLE in SQL Server somehow, simply by using SSMS and its features?
Don't give users permissions to drop tables.
You might think a DDL trigger can prevent this. It does, in a way: it lets the drop happen, then it rolls it back. Which is not quite preventing it, but I suppose it might be good enough.
Check this , There are two methods basically
The first one is based on creating a view on the table with option
SCHEMABINDING. When the SCHEMABINDING option is used the table cannot
be modified in a way that will affect the view definition, as well as
it cannot be dropped unless the view is dropped first.
The second method is using the new DDL triggers in SQL Server 2005.
Defining a trigger for DROP_TABLE with rollback in the body will not
allow dropping tables.
I am trying to dynamically create a SQL table only if it's not already existing. I have seen many solutions on the internet but they usually rely on a specific database, while I'm trying to find the most generic solution.
I was thinking of always running the CREATE command and then assuming that if it fails then the table exist and I can start inserting data into it. I can't see any flaw in this reasoning (not counting performance issues), but I might be wrong.
Is this an acceptable method?
Can you suggest other methods which are database independent, or that use ANSI SQL that all RDBMS would accept?
if there is a table - say - EMP, does that really imply that it is the same EMP that you are expecting?
Either query the appropriate data dictionary for the table structure, or fill your code with a ton of error checking and conditional logic...
INFORMATION_SCHEMA is part of the ANSI SQL Standard, so you should be able to:
IF NOT EXISTS(SELECT NULL FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = 'YourTable')
CREATE TABLE...
what about: create table if not exists
I have been developing an asp.net mvc site on a local version of sql server express 2008 and about a month ago I set up the web host and got everything working, the host uses sql server 2005. The site is not live.
Now a month down the track I need to do a fairly big update and the database is way out of date.
I would like to know how I can retain the database but blow everything else away (tables etc.) so I can run the set up script again.
When I try a few things I find on the internet it complains about the foreign keys and doesn't delete.
Thanks in advance
if you truly don't need to retain anything (including users, roles, UDTs, etc), then just drop the db and create a new one.
Take a look at this answer to a question about disabling FK constraints, and rejoice! :)
my guess: it's all about the order you drop the tables
ex
table1
key
fKeyTable2 (foreignkey from table 2)
table2
key
first drop table 2, then drop table1
if its hard to figure out the order you can try this:
ALTER TABLE tbl_name DROP FOREIGN KEY fk_symbol;
(fk_symbol = the foreign key that is being complained about)
Is it possible to create more than one table at a time using single create table statement.
For MySQL, you can use multi-query to execute multiple SQL statements in a single call. You'd issue two CREATE TABLE statements separated by a semicolon.
But each CREATE TABLE statement individually can create only one table. The syntax supported by MySQL does not allow multiple tables to be created simultaneously.
#bsdfish suggests using transactions, but DDL statements like CREATE TABLE cause implicit transaction commits. There's no way to execute multiple CREATE TABLE statements in a single transaction in MySQL.
I'm also curious why you would need to create two tables simultaneously. The only idea I could come up with is if the two tables have cyclical dependencies, i.e. they reference each other with foreign keys. The solution to that is to create the first table without that foreign key, then create the second table, then add the foreign key to the first table with ALTER TABLE ADD CONSTRAINT. Dropping either table requires a similar process in reverse.
Not with MS SQL Server. Not sure about mysql.
Can you give more info on why you'd want to do this? Perhaps there's an alternative approach.
I don't know, but I don't think you can do that. Why you want to do this?
Not in standard SQL using just the 'CREATE TABLE' statement. However, you can write multiple statements inside a CREATE SCHEMA statement, and some of those statements can be CREATE TABLE statements. Next question - does your DBMS support CREATE SCHEMA? And does it have any untoward side-effects?
Judging from the MySQL manual pages, it does support CREATE SCHEMA as a synonym for CREATE DATABASE. That would be an example of one of the 'untoward side-effects' I was referring to.
(Did you know that standard SQL does not provide a 'CREATE DATABASE' statement?)
I don't think it's possible to create more than one table with a 'CREATE TABLE' command. Everything really depends on what you want to do. If you want the creation to be atomic, transactions are probably the way to go. If you create all your tables inside a transaction, it will act as a single create statement from the perspective of anything going on outside the transaction.