What follows are a number of useful SQL queries I have needed and am bound to forget if I don't make a note of them. I'll aim to add to this list as and when I come up against other non-trivial queries I'm bound to forget.

Query all locks on a database

SELECT  L.request_session_id AS SPID,
        DB_NAME(L.resource_database_id) AS DatabaseName,
        O.Name AS LockedObjectName,
        P.object_id AS LockedObjectId,
        L.resource_type AS LockedResource,
        L.request_mode AS LockType,
        ST.text AS SqlStatementText,       
        ES.login_name AS LoginName,
        ES.host_name AS HostName,
        TST.is_user_transaction as IsUserTransaction,
        AT.name as TransactionName,
        CN.auth_scheme as AuthenticationMethod
FROM    sys.dm_tran_locks L
        JOIN sys.partitions P ON P.hobt_id = L.resource_associated_entity_id
        JOIN sys.objects O ON O.object_id = P.object_id
        JOIN sys.dm_exec_sessions ES ON ES.session_id = L.request_session_id
        JOIN sys.dm_tran_session_transactions TST ON ES.session_id = TST.session_id
        JOIN sys.dm_tran_active_transactions AT ON TST.transaction_id = AT.transaction_id
        JOIN sys.dm_exec_connections CN ON CN.session_id = ES.session_id
        CROSS APPLY sys.dm_exec_sql_text(CN.most_recent_sql_handle) AS ST
WHERE   resource_database_id = db_id()
ORDER BY L.request_session_id

Count per hour

So imagaine you wanted to get the number of sales per hour, since a certain date.

SELECT
  DATEADD(HOUR, DATEDIFF(HOUR, 0, pr.Date), 0),
  p.Description,
  COUNT(*)
FROM
  PurchaseRecord pr
    INNER JOIN Product p ON
      p.Id = pr.ProductId
WHERE
  pr.Date > '2011-11-08 23:59:59.999'
GROUP BY
  DATEADD(HOUR, DATEDIFF(HOUR, 0, pr.Date), 0),
  p.Description 
ORDER BY
  DATEADD(HOUR, DATEDIFF(HOUR, 0, pr.Date), 0)

Diagram component installation issue

In the past I have had problems trying to install the MS-SQL diagram component, in order to generate schema diagrams. The following query has helped in the past.

EXEC sp_dbcmptlevel 'TestDatabase', '90';
go
ALTER AUTHORIZATION ON DATABASE::TestDatabase TO "sa"
go
use [TestDatabase]
go
EXECUTE AS USER = N'dbo' REVERT
Go