A cross join that does not have a WHERE clause produces the Cartesian product of the tables involved in the join. The size of a Cartesian product result set is the number of rows in the first table multiplied by the number of rows in the second table. The following example shows a Transact-SQL cross join.
However, if a WHERE clause is added, the cross join behaves as an inner join. For example, the following Transact-SQL queries produce the same result set.
Using CROSS APPLY (t-sql)
Given:
CREATE FUNCTION dbo.fn_GetTopOrders(@custid AS int, @n AS INT)
RETURNS TABLE
AS
RETURN
SELECT TOP(@n) *
FROM Sales.SalesOrderHeader
WHERE CustomerID = @custid
ORDER BY TotalDue DESC
GO
which returns the top n orders per customerID
SELECT C.CustomerID,
O.SalesOrderID,
O.TotalDue
FROM
AdventureWorks.Sales.Customer AS C
CROSS APPLY
AdventureWorks.dbo.fn_GetTopOrders(C.CustomerID, 3) AS O
ORDER BY
CustomerID ASC, TotalDue DESC
results in this…
CustomerID SalesOrderID TotalDue
———– ———— ———————
1 45283 37643.1378
1 46042 34722.9906
1 44501 26128.8674
2 46976 10184.0774
2 47997 5469.5941
2 57044 4537.8484
3 53616 92196.9738
3 47439 78578.9054
3 48378 56574.3871
4 47658 132199.8023
. . .
The APPLY clause acts like a JOIN without the ON clause comes in two flavors: CROSS and OUTER.
The OUTER APPLY clause returns all the rows on the left side (Customers)
whether they return any rows in the table-valued-function or not (the “LEFT JOIN” table).
The columns that the table-valued-function returns are null if no rows are returned.
The CROSS APPLY only returns rows from the left side (Customers)
if the table-valued-function returns rows.
Notice that I’m just passing in the CustomerID to the function.
It returns the TOP 3 rows based on the amount of the order.
Since I’m using CROSS APPLY a customer without orders won’t appear in the list.
I can also pass in a number other than 3 to easily return a different number of orders per customer.
Even better I can pass in a different number of orders for each customer.
So I could list the top 5 orders for one type of customer but the top 10 for another type of customer.
How cool is that?!?
And it gets even better.
Remember the function has an ORDER BY in it.
It will always return the top orders based on the amount.
However you can change the ORDER BY clause in the query that calls the function to display those rows in whatever order you want.
You could easily display the top 3 orders in ascending order instead.
[SQL] @@Identity, SCOPE_IDENTITY()
msdn link
SCOPE_IDENTITY, IDENT_CURRENT, and @@IDENTITY are similar functions because they return values that are inserted into identity columns.
IDENT_CURRENT is not limited by scope and session; it is limited to a specified table. IDENT_CURRENT returns the value generated for a specific table in any session and any scope. For more information, see IDENT_CURRENT (Transact-SQL).
SCOPE_IDENTITY and @@IDENTITY return the last identity values that are generated in any table in the current session. However, SCOPE_IDENTITY returns values inserted only within the current scope; @@IDENTITY is not limited to a specific scope.
For example, there are two tables, T1 and T2, and an INSERT trigger is defined on T1. When a row is inserted to T1, the trigger fires and inserts a row in T2. This scenario illustrates two scopes: the insert on T1, and the insert on T2 by the trigger.
Assuming that both T1 and T2 have identity columns, @@IDENTITY and SCOPE_IDENTITY will return different values at the end of an INSERT statement on T1. @@IDENTITY will return the last identity column value inserted across any scope in the current session. This is the value inserted in T2. SCOPE_IDENTITY() will return the IDENTITY value inserted in T1. This was the last insert that occurred in the same scope. The SCOPE_IDENTITY() function will return the null value if the function is invoked before any INSERT statements into an identity column occur in the scope.
Failed statements and transactions can change the current identity for a table and create gaps in the identity column values. The identity value is never rolled back even though the transaction that tried to insert the value into the table is not committed. For example, if an INSERT statement fails because of an IGNORE_DUP_KEY violation, the current identity value for the table is still incremented.
Gleamed from akadia.com
SQL Server Logins and Users
Overview
Although the terms login and user are often used interchangeably, they are very different.
Logins are associated to users by the security identifier (SID).
A login is required for access to the SQL Server server. The process of verifying that a particular login is valid is called “authentication”. This login must be associated to a SQL Server database user. You use the user account to control activities performed in the database. If no user account exists in a database for a specific login, the user that is using that login cannot access the database even though the user may be able to connect to SQL Server. The single exception to this situation is when the database contains the “guest” user account. A login that does not have an associated user account is mapped to the guest user. Conversely, if a database user exists but there is no login associated, the user is not able to log into SQL Server server.
When a database is restored to a different server it contains a set of users and permissions but there may not be any corresponding logins or the logins may not be associated with the same users. This condition is known as having “orphaned users.”
Troubleshooting Orphaned Users
When you restore a database backup to another server, you may experience a problem with orphaned users. The following scenario illustrates the problem and shows how to resolve it.
Use master
sp_addlogin ‘test’, ‘password’, ‘Northwind’SELECT sid FROM dbo.sysxlogins WHERE name = ‘test’
0xE5EFF2DB1688C246855B013148882E75
Use Northwind
sp_grantdbaccess ‘test’
SELECT sid FROM dbo.sysusers WHERE name = ‘test’
0xE5EFF2DB1688C246855B013148882E75
As you can see, both SID’s are identical.
Backup the database
Use master
BACKUP DATABASE Northwind
TO DISK = ‘C:\Northwind.bak’
Copy the Backupfile to another Maschine and SQL Server and restore it as follows:
RESTORE FILELISTONLY
FROM DISK = ‘C:\Users\Zahn\Work\Northwind.bak’
Northwind
Northwind_logRESTORE DATABASE TestDB
FROM DISK = ‘C:\Users\Zahn\Work\Northwind.bak’
WITH
MOVE ‘Northwind’ TO ‘D:\DataMSSQL\Data\northwnd.mdf’,
MOVE ‘Northwind_log’ TO ‘D:\DataMSSQL\Data\northwnd.ldf’
The restored database contains a user named "test" without a corresponding login, which results in "test" being orphaned.
Check the SID's
Use master
SELECT sid FROM dbo.sysxlogins WHERE name = ‘test’
0x39EE98D37EAC2243B7833705EC1C60E3Use TestDB
SELECT sid FROM dbo.sysusers WHERE name =’test’
0xE5EFF2DB1688C246855B013148882E75
Now, to detect orphaned users, run this code
Use TestDB
sp_change_users_login ‘report’
test 0xE5EFF2DB1688C246855B013148882E75
The output lists all the logins, which have a mismatch between the entries in the sysusers system table, of the TestDB database, and the sysxlogins system table in the master database.
Resolve Orphaned Users
Use TestDB
sp_change_users_login ‘update_one’, ‘test’, ‘test’SELECT sid FROM dbo.sysusers WHERE name = ‘test’
0x39EE98D37EAC2243B7833705EC1C60E3use master
SELECT sid FROM dbo.sysxlogins WHERE name =’test’
0x39EE98D37EAC2243B7833705EC1C60E3
This relinks the server login “test” with the the TestDB database user “test”.
The sp_change_users_login stored procedure can also perform an update of all orphaned users with the “auto_fix” parameter but this is not recommended because SQL Server attempts to match logins and users by name.
For most cases this works; however, if the wrong login is associated with a user, a user may have incorrect permissions.
Gleamed from MSDN library
SQL Server 2000 Controls the default transaction locking behavior for all Microsoft® SQL Server™ SELECT statements issued by a connection.
Syntax
SET TRANSACTION ISOLATION LEVEL
{ READ COMMITTED
| READ UNCOMMITTED
| REPEATABLE READ
| SERIALIZABLE
}
Arguments
Remarks
Only one of the options can be set at a time, and it remains set for that connection until it is explicitly changed. This becomes the default behavior unless an optimization option is specified at the table level in the FROM clause of the statement.
The setting of SET TRANSACTION ISOLATION LEVEL is set at execute or run time and not at parse time.
Examples
This example sets the TRANSACTION ISOLATION LEVEL for the session. For each Transact-SQL statement that follows, SQL Server holds all of the shared locks until the end of the transaction.
SET TRANSACTION ISOLATION LEVEL REPEATABLE READ
GO
BEGIN TRANSACTION
SELECT * FROM publishers
SELECT * FROM authors
…
COMMIT TRANSACTION
Care of David Poole of SQLServerCentral: http://www.sqlservercentral.com/articles/Documentation/72473/
RAISERROR ( ‘DATA DICTIONARY: %i tables & %i fields added’, 10, 1,
@TableCount, @FieldCount ) WITH NOWAIT
The “10” parameter is the SEVERITY of the error message raised.
10 : this is more of a notice message, or minor alert
16 : this is reserved for true error messages
You can find more via:
Care of http://www.mssqltips.com/tutorial.asp?tutorial=179
Overview
The INFORMATION_SCHEMA views allow you to retrieve metadata about the objects within a database. These views can be found in the master database under Views / System Views and be called from any database in your SQL Server instance. The reason these were developed was so that they are standard across all database platforms. In SQL 2005 and SQL 2008 these Information Schema views comply with the ISO standard.
Following is a list of each of the views that exist.
These views can be used from any of your databases. So if you want to gather data about Tables from the AdventureWorks database you would issue the following in that database.
|
USE AdventureWorks |
Posted in SQL
http://msdn.microsoft.com/en-us/library/aa259216(SQL.80).aspx
[READ UNCOMMITTED]
Implements dirty read, or isolation level 0 locking, which means that no shared locks are issued and no exclusive locks are honored.
When this option is set, it is possible to read uncommitted or dirty data; values in the data can be changed and rows can appear or disappear in the data set before the end of the transaction.
This option has the same effect as setting NOLOCK on all tables in all SELECT statements in a transaction.
This is the least restrictive of the four isolation levels.
Posted in SQL
http://msdn.microsoft.com/en-us/library/aa259216(SQL.80).aspx
[READ UNCOMMITTED]
Implements dirty read, or isolation level 0 locking, which means that no shared locks are issued and no exclusive locks are honored. the end of the transaction.
This option has the same effect as setting NOLOCK on all tables in all SELECT statements in a transaction.
This is the least restrictive of the four isolation levels.
When this option is set, it is possible to read uncommitted or dirty data; values in the data can be changed and rows can appear or disappear in the data set before
Posted in SQL
The APPLY clause let’s you join a table to a table-valued-function.
The APPLY clause acts like a JOIN without the ON clause comes in two flavours: CROSS and OUTER.
The OUTER APPLY clause returns all the rows on the left side table whether they return any rows in the table-valued-function or not, and thus similar to a left join).n
The columns that the table-valued-function returns are null if no rows are returned.
The CROSS APPLY only returns rows from the left side table if the table-valued-function returns rows.
http://msdn.microsoft.com/en-us/library/ms175156.aspx
http://www.sqlteam.com/article/using-cross-apply-in-sql-server-2005
http://www.sqlusa.com/articles2005/crossapplyversusouterapply/
Posted in SQL
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