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.
Related
I want to truncate all tables under a specific schema in DB2 which is worked on a Linux Server. But I have no right to ALTER TABLE to disable the foreign-key constraints.
Is there anyway to do this?
I'm considering performing a topology sort based on the constraints between tables, but it is a little bit complex.
Any good idea on this problem?
You don't say what platform you're on. This answer is specific to DB2 on Linux, UNIX and Windows.
If you have LOAD, INSERT and DELETE privileges on the table(s) you can use the LOAD command with an empty file to truncate the tables, regardless of whether there are foreign key constraints:
LOAD from /dev/null of del replace into yourschema.yourtable nonrecoverable
This will place any dependent tables in check pending state… Once you have truncated all of your tables you would use the SET INTEGRITY statement to take all of the tables out of check pending.
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.
What is the default locking mechanism in PostgresSQL when we create a table ? is it row, page, table level or something else?
Is it possible to specify row level locking when we create a table ? something like below in Sybase.
CREATE TABLE user
(...)
LOCK DATRAROWS
Or do we not need to specify any locking strategy and leave it to Postgres to choose the best while we dealing CRUD ?
Cheers!
There isn't anything you can specify at CREATE TABLE time for PostgreSQL. At run time, you can select rows FOR UPDATE or FOR SHARE. If you're coming to PostgreSQL from another platform, you should skim the docs on concurrency control.
There is no locking when you create a table.
Locking can be read here: http://www.postgresql.org/docs/9.0/static/explicit-locking.html
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.
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.